Target CO2
What is the long term sensitivity to increasing CO2? What, indeed, does long term sensitivity even mean? Jim Hansen and some colleagues (not including me) have a preprint available that claims that it is around 6ºC based on paleo-climate evidence. Since that is significantly larger than the 'standard' climate sensitivity we've often talked about, it's worth looking at in more detail.
We need to start with some definitions. Sensitivity is defined as the global mean surface temperature anomaly response to a doubling of CO2 with other boundary conditions staying the same. However, depending on what the boundary conditions include, you can get very different numbers. The standard definition (sometimes called the Charney sensitivity), assumes the land surface, ice sheets and atmospheric composition (chemistry and aerosols) stay the same. Hansen's long term sensitivity (which might be better described as the Earth System sensitivity) allows all of these to vary and feed back on the temperature response. Indeed, one can imagine a whole range of different sensitivities that could be clearly defined by successively including additional feedbacks. The reason why the Earth System sensitivity might be more appropriate is because that determines the eventual consequences of any particular CO2 stabilization scenario.
Traditionally, the decision to include or exclude a feedback from consideration has been based on the relevant timescales and complexity. The faster a feedback is, the more usual it is to include. Thus, changes in clouds (~hours) or in water vapour (~10 days) are undoubtedly fast and get included as feedbacks in all definitions of the sensitivity. But changes in vegetation (decades to centuries) or in ice sheets (decades(?) to centuries to millennia) are slower and are usually left out. But there are other fast feedbacks that don't get included in the standard definition for complexity reasons - such as the change in ozone or aerosols (dust and sulphates for instance) which are also affected by patterns of rainfall, water vapour, temperature, soli moisture, transport and clouds (etc.).
Not coincidentally, the Charney sensitivity corresponds exactly to the sensitivity one gets with a standard atmospheric GCM with a simple mixed-layer ocean, while the Earth System sensitivity would correspond to the response in a (as yet non-existent) model that included interactive components for the cryosphere, biosphere, ocean, atmospheric chemistry and aerosols. Intermediate sensitivities could however be assessed using the Earth System models that we do have.
In principal, many of these sensitivities can be deduced from paleo-climate records. What is required is a good enough estimate of the global temperature change and measures of the various forcings. However, there are a few twists in the tale. Firstly, getting 'good enough' estimates for global temperatures changes is hard - this has been done well for the last century or so, reasonably for a few centuries earlier, and potentially well enough for the really big changes associated with the glacial-interglacial cycle. While sufficient accuracy in the last few centuries is a couple of tenths of a degree, this is unobtainable for the last glacial maximum or the Pliocene (3 million years ago). However, since the signal is much larger in the earlier periods (many degrees), the signal to noise ratio is similar.
Secondly, although many forcings can be derived from paleo-records (long-lived greenhouse gases from bubbles in the ice cores most notably), many cannot. The distribution of sulphate aerosols even today is somewhat uncertain, and at the last glacial maximum, almost completely unconstrained. This is due in large part to the heterogenity of their distribution and there are similar problems for dust and vegetation. In some sense, it is the availability of suitable forcing records that suggests what kind of sensitivity one can define from the record. A more subtle point is that the 'efficacy' of different forcings might vary, especially ones that have very different regional signatures, making it more difficult to add up different terms that might be important at any one time.
Lastly, and by no means leastly, Earth System sensitivity is not stable over geologic time. How much it might vary is very difficult to tell, but for instance, it is clear that from the Pliocene to the Quaternary (the last ~2,5 million years of ice age cycles), the climate has become more sensitive to orbital forcing. It is therefore conceivable (but not proven) that any sensitivity derived from paleo-climate will not (in the end) apply to the future.
We've often gone over the Charney sensitivity constraint for the Last Glacial Maximum. There is information about the greenhouse gases (CO2, CH4 and N2O), reconstructions of the ice sheets and vegetation change, and estimates of the dust forcing. A recent estimate of the magnitude of these forcings is around 8 +/- 2 W/m2 (Schneider von Deimling et al, 2006). This implicitly includes other aerosol changes or atmospheric chemistry changes in with the sensitivity (or equivalently, assumes that their changes are negligible). So given a temperature change of about 5 to 6ºC, this gives a Charney sensitivity of around 3ºC (ranging from 1.5 to 6 if you do the uncertainty sums).
Hansen suggests that the dust changes should be considered a fast feedback as well (as could the CH4 changes?) and that certainly makes sense if vegetation changes are included on the feedback side of the equation. Since all of these LGM forcings are the same sign (i.e. they are all positive feedbacks for the long term temperature change), that implies that the Earth System sensitivity must be larger than the Charney sensitivity on these timescales (and for this current geologic period). So far so good.
Hansen's first estimate of the Earth System sensitivity is based on an assumption that GHG changes over the long term control the amount of ice. That gives a scaling of 6ºC for a doubling of CO2. This is however problematic for two reasons; first most of the power of this relationship is derived from when there were large N. American and European ice sheets. It is quite conceivable that, now that we are left with only Greenland and Antarctica, the sensitivity of the temperature to the ice sheets is less. Secondly, it subsumes the very special nature of orbital forcing - extreme regional and seasonal impacts but very little impact on the global mean radiation. Hansen's estimate assumes that an overall cooling of the same magnitude of the LGM would produce the same extent of ice sheets that was seen then. It may be the case, but it is not a priori obvious that it must be. Hansen rightly acknowledges these issues, and suggests a second constraint based on longer term changes.
Unfortunately, prior to the ice core record, our knowledge of CO2 changes is much poorer. Thus while it seems likely that CO2 decreased from the Eocene (~50 million years ago) to the Quaternary through variations related to tectonics, the exact magnitude is uncertain. For reasonable values based on the various estimates, Hansen estimates a ~10 W/m2 forcing change over the Cenozoic from this alone (including a temperature-related CH4 change). The calculation in the paper is however a little more subtle. Hansen posits that the long term trend in the deep ocean temperature in the early Cenozoic period (before there was substantial ice) was purely due to CO2 (using the Charney sensitivity). He then plays around with the value of the CO2 concentration at the initiation of the Antarctic ice sheets (around 34 million years ago) to get the best fit with the CO2 reconstructions over the whole period. What he ends up with is a critical value of ~425 ppm for initiation of glaciation. To be sure, this is fraught with uncertainties - in the temperature records, the CO2 reconstructions and the reasonable (but unproven) assumption concerning the dominance of CO2. However, bottom line is that you really don't need a big change in CO2 to end up with a big change in ice sheet extent, and that hence the Earth System sensitivity is high.
So what does this mean for the future? In the short term, not much. Even if this is all correct, these effects are for eventual changes - that might take centuries or millennia to realise. However, even with the (substantial) uncertainties in the calculations and underlying assumptions, the conclusion that the Earth System sensitivity is greater than the Charney sensitivity is probably robust. And that is a concern for any policy based on a stabilization scenario significantly above where we are now.
7 avril 2008 at 8:54 AM
There are a few observations in this which makes the high sensitivity for GHGs rather questionable.
In the first place, GHGs in the pre-industrial past follow orbital/temperature changes, don’t lead. This is clear from the detailed Epica Dome C ice core, where CO2 trends follow the d18O (temperature proxy) trend in the LGM-Holocene transition, with no measurable feedback from increasing CO2 levels.
See here (with thanks to André van den Berg for the graph).
Secondly, orbital changes have their effect mainly in the (sub)tropics and may have a different effect on e.g. cloud cover (which are in reverse correlation with total solar irradiance) than more evenly distributed GHGs. Thus the effect of one W/m2 from GHGs doesn’t necessary equals the effect of one W/m2 from orbital changes…
[Response: There is plenty of evidence showing that the GHG changes contribute to the amplitude of the ice-age cycles. The graph you show simply demonstrates that the deglaciation was complex. Given the impacts of adding 120 meters equivalent of global mean sea level equivalent of freshwater to the system are unlikely to be negligible on ocean circulation and biological activity. Similarly, the different timescales for land biospheric changes and ice sheet changes will almost certainly give a complex transient scenario. That is very interesting, and indeed, largely uncertain, but as a demonstration there is no CO2 impact on climate it falls very short.
As to oribital forcing regionally having a different effect to global mean forcings, I specifically state that above and discuss the implications for Hansen’s argument. - gavin]
7 avril 2008 at 9:21 AM
This paper has been picked up by this morning’s Guardian newspaper here in the UK, which ran it as the front page lead.
That report was in turn picked up by The Register, a well-known UK IT (and related issues) site, which has recently been sullying it’s generally excellent record for debunking popular myths or the hype-du-jour by jumping to entirely the wrong side of the popular debate on AGW.
7 avril 2008 at 9:32 AM
I am on an international socials commentary e mail list. We have had discussions on global warming on that list, and I must admit that a few of those on the list have been taken in by the deniers. I have had some very sharp debates with them. In any case, one person posted the following note, which quotes an article from the “Guardian” newspaper. Can somebody explain this for me? Thank you.
“Hansen’s team studied core samples taken from the bottom of the
ocean, which allow C02 levels to be tracked millions of years ago.
They show that when the world began to glaciate at the start of the
Ice age about 35m years ago, the concentration of CO2 in the
atmosphere stood at about 450ppm.”
This makes no sense as it stands in the light of present targets for
CO2 emissions; I read it as saying that we should be aiming for a CO2
concentration which would be the SAME at the start of the last Ice
Age, at the time when the earth started to glaciate.
But then it goes on:
“If you leave us at 450ppm for long enough it will probably melt all
the ice - that’s a sea rise of 75 metres. What we have found is that
the target we have all been aiming for is a disaster - a guaranteed
disaster.”
If 450ppm were compatible with a long, long Ice Age and global
glaciation 35m years ago, how is it that exactly the same level today or in the future would be expected to cause global warming?
7 avril 2008 at 9:57 AM
If someone could give a brief explanation about what an ‘orbital forcing’ is opposed to simply a ‘forcing’ then I’d be very grateful. I’ve got a fair understanding of the latter but don’t understand what the ‘orbital’ part means. Thank you.
[Response: It refers specifically to the changes in the distribution of solar radiation over latitude and season that occur because of variations in the precession, obliquity and eccentricity of the Earth’s orbit. Otherwise known as Milankovitch forcings. - gavin]
7 avril 2008 at 10:08 AM
“A more subtle point is that the ‘efficacy’ of different forcings, especially ones that have very regional signatures might vary, making it more difficult to add up different terms that might be important at any one time.”
Should this be: A more subtle point is that the ‘efficacy’ of different forcings might vary, especially ones that have very *different* regional signatures, making….? A bit hard to parse as well as a missing word.
[Response: thanks. I made the correction. - gavin]
7 avril 2008 at 10:13 AM
#3 - I think the language the Guardian uses is a bit confused. If you look at the ice cores, then over the recent ice-age cycles CO2 goes up to a high-point of about 280ppm in the interglacials and is lower than that during the glacial maximums.
I think the 450ppm 35 million years ago is referring to a time *before* the current geologic period of ice-age cycles. What they argue is that if the 450ppm is sustained over geologic timescales ie >1000-10000 years then it will lead to the loss of all ice.
That seems reasonable to me, but I don’t think it has any bearing on policy, since CO2 levels are already above 380ppm and rising rapidly. We have to work out a way of stabilising those levels during this century and *then* we can work out how we’re going to reduce them back down again (or whether the carbon cycle will do it for us quickly enough).
The East Antarctic Ice Sheet is going to give us more than a century of breathing space to sort things out, and if it doesn’t, well, there’s not much we can do to avoid that, so we’d better hope that it does.
7 avril 2008 at 10:14 AM
Re #3 The first x million years of antartic glaciation 34 million years ago was unstable and did not become stable until 18 million years ago when CO2 levels had fallen slightly lower I believe. worryingly Northern Hemisphere Ice sheets did not begin to form until 400 ppmv but I do not know when they became stable CO2 levels wise. If we take into account the differences in orbital forcings 34 million years ago and the levels of other greenhouse gases and the amount of vegetation on the planet I would agree with James Hansen that climate sensitivity is possibly higher than it was way bacj then.
7 avril 2008 at 10:42 AM
The six degree long term climate sensitivity seems to largely depend on the CO2 level when Antarctica began to be glaciated about 35 million years ago. I am having trouble understanding how a 425 ppm level of CO2 at that time was arrived at. From looking at the curves, it does not appear any of them really fits very well, so this data is not adequate to arrive at such a conclusion.
I also want to question the assumption that the temperature (thus CO2 level) at which glaciation begins is the same one that will melt the ice cap entirely. An ice cap creates it own regional climate, as can be seen by the contrast between Antarctica and the Arctic. Therefore I would assume that the temperature required to melt an ice cap is significantly higher than the temperature it formed at.
On the other hand, this view seems to contradict the observation that the warming period for interglacial periods is shorter than the cooling period of re-entering the ice age.
7 avril 2008 at 10:48 AM
“I would assume that the temperature required to melt an ice cap is significantly higher than the temperature it formed at.”
I believe this is the state the Greenland ice cap is in now - ie it is only there because it is already there, and if it melts there’s no way to get it back without another ice age. Indeed, if it starts to melt, then presumably its height will decrease and the melting will accelerate.
So, yes, I think I would now agree with you that it is a bit of a leap of faith to assume that 450 ppm would see the eventual demise of the Antarctic Ice Sheet.
7 avril 2008 at 11:00 AM
“So what does this mean for the future? In the short term, not very much”.
Well, if Hansen is right, that depends on what you mean by “short-term”. To quote from the preprint:
“Sea level changes of several meters per century occur in
the paleoclimate record, in response to forcings slower and weaker than the present human-made forcing. It seems likely that large ice sheet response will occur within centuries, if human-made forcings continue to increase. Once ice sheet disintegration is underway, decadal changes of sea level may be substantial.”
The Guardian article A. Simmons referred to quotes him as saying: “We are talking about a sea-level rise of at least a couple of metres this century.”
So far as I can see, he could be right about that, without being right about the long-term/Earth System climate sensitivity being as high as 6 degrees C. He’s suggesting that previous ice-sheet melting episodes were slow because the forcing due to orbital change was slow, not due to inherent inertia, and that recent observation suggests ice-sheets can melt much faster if the forcing is faster.
[Response: I wasn’t talking about sea level - but just to make it clear, I share Jim’s concern that serious sea level changes are a real possibility. None of the long term sensitivity issues deal with the problem of rates of change, and so the preprint or this post cannot really address that. - gavin]
7 avril 2008 at 11:20 AM
Do you mean by, “simple mixed layer ocean” that the variations of ocean temperature with depth are not part of the analysis?
[Response: In the standard estimate of the Charney sensitivity. no. Using fully coupled OAGCMs takes much much longer and has not yet become standard practice. In the GISS models, the difference in eventual temperatures (after hundreds of years) is on the order of a few tenths of a degree. - gavin]
7 avril 2008 at 11:32 AM
On the issue of the orbital forcing changes though - Hansen isn’t even looking at the forcing going all the way back to the orbital effects in this paper, he’s just looking at the CO2 levels as if they are the forcing. The actual forcing from the orbital changes is presumably smaller (or is it effectively large when you account for latitudinal dependence?) - i.e. if CO2 levels themselves are a positive feedback of a factor 3 or so on the orbital forcings, then doesn’t that further multiply the actual sensitivity to fundamental forcing by a factor of 3, i.e. 18 C instead of 6?
The point is: it’s widely recognized that CO2 levels in the atmosphere increase as a result of temperature increases, a positive feedback effect. Climate models and Charney analysis effectively ignore this because they’re looking at the effect of increased CO2 itself.
But if our interest is in the effect of *anthropogenic* CO2 only, which is a real forcing, then the feedback CO2 could be tremendously additive. I.e. if you look at the target for CO2 emissions by humans, rather than just the target CO2 level in the atmosphere, the constraint is that much more stringent. To keep to 350 ppm, which already means a long-term warmer world, we may have to go to zero or less-than-zero human emission levels. But I’d like to see that quantified a bit better…
7 avril 2008 at 11:57 AM
Re:#3
John Reimann
“If 450ppm were compatible with a long, long Ice Age and global
glaciation 35m years ago, how is it that exactly the same level today or in the future would be expected to cause global warming?”
Prior 35m years ago the earth did not have large ice sheets like today. As the temperature sinks below a special value the Antarctic ice sheet growth.
If the temperature rise in the future above a similar (but somewhat higher value, see post#8) value for a long time, the ice sheet will melt.
The sun is now somewhat brighter the 35m ago, which lowers the CO2 level needed to reach this temperature.
On the other hand the higher albedo of the ice sheets will rise the level of CO2 needed to this temperature.
The problem is, that the exact temperature is not well known.
7 avril 2008 at 12:04 PM
I am a little confused. You mention that slower feedbacks are excluded from definitions of sensitivity, which is reasonable; sensitivity must be defined on a relevant time scale.
However, does this mean that those slower feedbacks are excluded from coupled model formulations? I thought I’d seen mentions of afforestation or predictive vegetation in the IPCC report.
Could somebody address the sign, magnitude and time scale of feedbacks related to vegetation changes? I’d imagine that increased vegetation would result in a larger carbon sink, but there would be changes in surface albedo and transpiration along with it.
[Response: Most GCMs do not consider vegetation feedbacks (and all ’sensitivity’ numbers you will have seen, do not include them either) - but it is becoming more common and most groups have, or are working on, such modules. Some of the early experiments (by Peter Cox, Pierre Freidlingstein etc.) show positive feedbacks on CO2 levels (of varying degrees) and, presumably, some impact on temperature due to albedo/ET effects. I am not however aware of what they are (maybe someone more knowledgeable could comment?). - gavin]
7 avril 2008 at 12:09 PM
Gavin,
While I appreciate your effort to keep the long millennial timescale in consideration, I think it worth stressing that Hansen et al. have been looking hard at the timescale for the response of icesheets and find evidence that it is centuries rather than millennia. And they stress this also now:
If so, then slow feedbacks may not be all that slow and the present day policy implications rather large.
It is worth noting that the preprint calls for stabilization below the current concentration of CO2 in the atmosphere and for active measures to remove CO2 from the atmosphere while providing a senario for how this might happen.
If if a policy of adaptation rather than mitigation is pursued, measures must also be taken now for projects that require 100 year plus planning horizons such as building dykes or sea walls or siting nuclear reactors. And, without a firm committment to mitigation, adaptation measures can’t be left unconsidered, doubling or more the present day cost of response. For example, the NRC is beginning to entertain an application for a new reactor at Calvert Cliffs on the Chesapeake Bay. This might be considered an aspect of mitigation, but it would be foolhardy not to consider what impact 5 meters of sea level rise before the planned end of decommissioning might have and build in adaptation measures now such as siting the plant further inland where the foundation would not be subject to erosion. A dyke to protect Long Island and it’s neighbors might need its foundation laid within a decade and its cost planned for in tax policy within a few years. Transportation planning also has long term aspects such as the interstate highway system. How soon must we start to elevate I-10 even higher to get the job done in time and at what cost?
So, I would argue that in the short term this work means quite a lot.
[Response: Please don’t misunderstand me - the eventual long term temperature change being 6 deg is the thing that I’m not sure has short term implications. But that is a statement about how changes in T affect ice sheets (etc.) which then affect T again. That is very different from saying that T affects ice sheets (and sea level) which is a much more serious short term issue and would be even if the long term sensitivity was the same as the Charney one. - gavin]
7 avril 2008 at 1:02 PM
Re 14:
I am no expert in this and don’t know much about terrestrial ecosystems except that they are generally considered to be substantially more complex than ocean ecosystems. I’ve read a few papers on ocean ecosystem modeling and would argue that our understanding of the crucial processes is still quite primitive. For example one ocean ecosystem model that I know is used in at least one GCM does not include any sort of parameterization related to ocean acidity. If large scale changes in the ocean ecology occur because of acidification the model cannot reasonably be expected to capture the effects. Moreover the key organisms and the dynamics between them is poorly understood at best.
I would also argue that the state of our understanding of the carbon cycle as it operates now is still pretty uncertain. There were papers published last year on the missing sink (the gigaton of CO2 that is taken up by unknown processes) like this one: Stephens, B. et al. Science 316, 1732–1735 (2007).
7 avril 2008 at 1:20 PM
Re 11 Thanks gavin,
So we know that there is no accounting for a controlling process whereby an increase in ocean surface temperature causes an increase in storm activity. Hurricane formation is a particularly strong example of this. That increase in storm activity causes mixing of the ocean such that colder waters from deeper regions are brought up such that the “mixed layer” is cooled. This reverses the initial temperature increase of the ocean surface. There is abundant cold water to handle this for a long time.
If this is the governing process, global warming will be seen as a very slight increase in ocean surface temperature. Only over a long time will there be a measurable increase in surface temperature. Before that happens, there should be a measurable increase in the “mixed layer depth”.
Since deeper waters will be warmer, there is a possible link to the global ocean circulating currents that results in warmer water in polar regions. This could be related to loss of ice, especially ice that is in ocean contact.
It seems that a quantitative study might result in better understanding of temperature changes. It does not appear that this is being done. From what you say, it would be prohibitively time consuming?
7 avril 2008 at 1:34 PM
I’ve been keen to read the Real Climate response to Hansen’s paper for a couple of weeks, and thanks very much for it. I suppose, however, that I remain confused about the implications, even having read Gavin’s response to #15. Please forgive me if I am slow!
The battle against climate change is based in no small part because of the alaming scientific understanding that we are potentially beginning long-term future processes that cannot be stopped. Short term concerns drive the headlines and insurance companies (and have the most emotive impact), but of course they are not the whole story. The bottom line is - what does the best science now suggest for a target that can be considered safe with reasonable probability? Is 450ppm becoming an inherently unsafe target for a long term habitable Earth? Is 350ppm the new 450ppm? Does the best advice to policymakers need an urgent review?
[Response: Nobody can say what is safe (in the long term), though we aren’t talking about making Earth inhabitable, just seriously uncomfortable for it’s existing inhabitants! As the levels rise, the consequences will get worse, and within those consequences will be dozens of thresholds and tipping points related to local or regional ecosystems and climate regimes - some which could have global consequences. We don’t know exactly where they are or what their effects will be, so the only prudent course is to try and avoid as many as possible. Thus in my opinion emissions should be lowered as fast and as soon as is technologically and economically feasible. Setting a target now doesn’t imply that people will not revise it downward later on in the process and so I don’t tend to get hung up on a precise target. - gavin]
7 avril 2008 at 1:37 PM
Jim #17, I think you are jumping to a lot of conclusions here. First, storms–even Cat 5 hurricanes are local and short-lived processes, whereas greenhouse forcing is operative 24/7/365. What is more, while such processes could well be important in the Southern Hemisphere, they will be less so in the Northern Hemisphere. Third, unless storm intensity increases drastically, the storms will foster exchange only down to a certain depth, and as waters at this depth warm, the effectiveness of this mechanism will decrease. Moreover, CO2 solubility will decrease. Thus, one could argue that the mechanism you posit is in fact hiding the warming that is going on, and that in the future (and CO2 persists for hundreds to thousands of years), the warming will be much more severe. In short, given that we already see significant warming occurring, I don’t think we can count on the oceans to save us.
7 avril 2008 at 2:07 PM
We might want to know that the discussion is moving to the courts:
Comer, et al. v. Murphy Oil USA, et al., in which a class of Mississippi property owners blame the environmental impact of energy and chemical companies for Hurricane Katrina damage. The case was dismissed during summary judgment in Mississippi federal court, but has since been appealed to the U.S. Court of Appeals for the 5th Circuit.
7 avril 2008 at 2:32 PM
RE #3 &
That 450 ppm also jarred me and my initial thought was the same as yours. Then I started thinking (aside from the points already raised), the earth was already in an initial cooling phase from some higher global temp. As denialists so like to point out, CO2 follows temp, and so when the temp (initially triggered by reduced solar irradiation??) lowered to that point at which ice sheets start to form, the CO2 was at 450 ppm. I understand from Lovelock’s REVENGE OF GAIA that plants & life in general do much better in cooler climates, so the plants started flourishing more and absorbing CO2 once the temp started decreasing from its high point, and the ice & snow increased the albedo and reduced temp more, and plants liked it even more with reduced temp from lower CO2 & increasing albedo, and the earth kept getting cooler with these cooling positive feedbacks (or swinging up and down, but on the whole headed down). I’m sort of imagining it as a direction and momentum thing — in the cooling direction.
Now we are adding CO2 so the effect is a warming trend, which reduces ice and snow albedo and releases carbon from frozen permafrost and ocean hydrates, and the direction and momentum are in the warming direction. And I think plants don’t very hot temps as much, especially the land being dissicated from the warmer air sucking out the moisture, and harm from droughts, floods, heat stress.
So perhaps there’s this issue of global temperature direction (cooling or warming) and system momentum.
Maybe that’s what “sensitivity” really has to do with — how much you have to poke the dragon to wake him from his sleep. Very little, it seems.
7 avril 2008 at 2:34 PM
I do not understand the second part of this statement from the Hansen paper:
First, I thought a warming climate reduced the temperature difference between the equator and poles, which is what drives most of the winds and ocean currents that cause ocean mixing. I would not think a small increase in hurricanes would compensate. In the deep past it is during warmer climates that you get a stratified and stagnant ocean.
Second, I did not think there was an excess of CO2 in the deep ocean, rather it would be in equilibrium with the lower CO2 levels of the past few million years. I would think that today’s higher CO2 levels would eventually increase levels in the deep ocean, though of course not quickly enough to solve our problems here on the surface.
7 avril 2008 at 3:38 PM
Arthur Smith (12) wrote “To keep to 350 ppm, which already means a long-term warmer world, we may have to go to zero or less-than-zero human emission levels.” The world is already at 385 ppm and adding 1–2 ppm per year. So to reach 350 ppm from just the current level requires removing about 185 GtC from the active carbon cycle.
Proposed methods to accomplish this include burning biofuels with CCS, as well as direct sequestration from the atmosphere, considered in a previous thread (down two).
And just briefly, without the reasoning, I suggest that even just 315 ppm is too high for long term climate stability.
7 avril 2008 at 3:45 PM
Gavin (in #15),
I think I see your distinction, we must wait for bare earth in the Antarctic for it to warm the Antarctic through albedo change, but since ice sheets have been grouped in as slow, I would still say that slow may not be so slow. And, this has a large effect. The total amplitude of the sensitivity revises the stabilization target downward, but a not so slow slow feedback also limits the amount of time we can be above that target. So, according to the preprint, we need to be cutting emissions very quickly now to avoid extra effort in cleaning up the atmosphere that would be the result of delay. And, we must perform that cleanup fairly quickly as well to reach the stabilization target soon. Letting the ecosystem do it on its own is not fast enough. If we had thousands of years for the slow feedbacks to come into effect, we might just wait, after cutting emissons, for the atmospheric concentration to fall just as we are doing with CFCs, but with a faster slow feedback, this would not be an option. So, at least for planning, the preprint has two large present day effects: a target below the current concentration and a need to take positive action beyond cutting emissions to meet that target.
7 avril 2008 at 4:54 PM
Interesting read, but…
We tend to focus in singular stuff instead of the whole. Sure, discussing CO2 is good, but consider some of the causes, say factories. What are they needed for? A consumption lifestyle. For whom? 6 billion people, who grow and consume more each day. Their lifestyle creates alienating neighbourhoods where we adapt to having cars etc. Can you walk 12 miles to the hospital? Maybe overpopulation is a legitimate concern, since it is not just consumption, but the scale of it, shaping our eco-system and society in a manner dependent on oil/consumption.
For a discussion on this, see this interview: http://www.corrupt.org/act/interviews/john_feeney
7 avril 2008 at 5:28 PM
Gavin wrote:
“Earth System sensitivity is not stable over geologic time. How much it might vary is very difficult to tell, but for instance, it is clear that from the Pliocene to the Quaternary (the last ~2,5 million years of ice age cycles), the climate has become more sensitive to orbital forcing.”
i seen to recall GCMs that attempted to model the closing and opening of ocean channels such as the Drake passage between Antarctica and S. America.
are there any (loooong range)models that take continental drift into account ?
tanx for another good column
sidd
7 avril 2008 at 6:56 PM
Re #3 I have an explanation of what was meant by the glaciation starting 35 million years ago. That was when ice first started appearing on the mountain tops of Antarctica.
It was only about 3 million years ago when ice sheets started forming in the Northern Hemisphere. It is their waxing and waning that produces the glacial/interglacials driven by Milankovitch cycles, which taken together are called the Great Ice Age.
In other words ice started forming in Antarctica 35 Ma ago, but the Ice Age did not start until the Isthmus of Panama closed 3 Ma ago, and ice sheets started forming in the Northern Hemisphere.
The level of CO2 at the start of the present inter-glacial 10 ka ago (the Holocene) was 260 ppm, and most of the Laurentian and Scandanavian ice sheets disappeared. See the Antarctic ice cores here for the CO2 level:
http://en.wikipedia.org/wiki/Image:Co2-temperature-plot.svg
During the previous inter-glacial (the Eemian) at around 130 ka ago the level of CO2 was at around 290 ppm and the Greenland ice began to melt as well, raising the sea level to about 5 m higher than today.
Now, with CO2 at 380 ppm both Greenland and the Antarctic Peninsula are melting, but not the Antarctic mountain ice sheets.
If all of Greenland melts we get a rise of 7 metres (20 feet). If ALL of Antarctica goes we get a rise of 70 m (200 feet, but CO2 levels are not high enough for that to happen yet!
7 avril 2008 at 7:23 PM
Gavin,
Y you wrote “So what does this mean for the future? In the short term, not much. Even if this is all correct, these effects are for eventual changes - that might take centuries or millennia to realise.”
It seems to me that there is a major flaw when thinking about ice sheets, which means an imminent danger is being ignored. Only the melting of continental ice sheets is being considered as a serious threat, because only they raise sea level. If the Arctic sea ice disappears sea level will change by only a few millimetres, and s it is not considered a danger.
But it will have a large effect on albedo! And that seems to be what this thread is about. Roughly a third of the multi-year Arctic sea ice disappeared last, and some Russians are predicting it will all be gone in another couple of years time. Whereas the greenhouse effect only increase with the log of gas concentration, albedo has a linear effect.
If melting ice sheets are a danger because of their effect on albedo, then the melting Arctic sea ice sheet rather belies your claim of what this means for the future when you wrote “In the short term, not much.”
Cheers, Alastair.
7 avril 2008 at 8:15 PM
Ray #19
Thanks for the response. I am trying not to come to any conclusions, and intended my words to be looking for comment.
But to clarify, I used the hurricane as a strong example, not meaning to exclude general wind processes.
Are you saying that ocean circulation patterns in the Northern Hemisphere do not reach Antarctic regions where ice is more in the water?
Also, why would CO2 solubility decrease if surface water warmed slightly and deeper water warmed more?
My premise is indeed that storms will foster exchange down to a depth such that the effectiveness of this mechanism will decrease, but then the level of storm activity would increase until the exchange went deeper. And yes, this would be hiding the warming that is going on. So I am suggesting that, maybe, without this process the ocean surface would be warmer than it is. I realize that the ARGO data discussed elsewhere is said to have been misinterpreted, but the actual numbers for surface temperature are not changing that much.
I also think I have heard that Antarctic ice is breaking up faster than expected.
Now back to hurricanes. Yes they are local, and short-lived, but they have powerful mixing effects that have a long lasting effect. We have actual knowledge of the strong deep currents in the gulf due to Katrina, from the fact that ocean floor pipelines were seriously damaged. I believe they were in water 1500 meters deep. The impact of this, via the gulf stream, would be spread over the entire North Atlantic, and it would last there quite some time.
But my point of view goes back to the practice of indirectly measuring the thermocline with a velocimeter as a part of underwater sound studies. This was the best way to relate temperatures to underwater sound propagation effects. More directly, Navy sonar operations used to include, and probably still do, a bathythermograph scan, “BT”, as a part of understanding how to best operate the sonar in a particular region to detect submarines, and the key depth of increased safety was the depth of the “layer.” The layer depth is thus known very well to vary significantly with wind effects, much less in strength than hurricanes. And we are talking about depths around 70 meters. That number is the transition between mixed conditions and rapidly cooling water depths. Below 600 meters, the oceans are almost universally cooler than 5 degrees C. About 85% of the oceans are 3000 to 6000 meters in depth. So we know very well that the reservoir of cold is large.
But my premise is not that the oceans will save us. If taken into account, it may be seen that they will slow the process as far as ocean surface temperature goes, and hence general air temperature. Further, the process I describe, while making surface temperature slow to change, could relate to ice melting activity.
But my premise is not that the oceans will save us. If taken into account, it may be seen that they will slow the process as far as ocean surface temperature goes, and hence general air temperature. Further, the process I describe, while making surface temperature slow to change, could relate to ice melting activity.
Eventually, as the depth necessary to tap into the cold gets lower, the storms will increase. Without benefit of analysis, I venture to guess this would be noticeable much sooner than a hundred thousand years. However, it might not be as soon as some are now saying.
7 avril 2008 at 8:47 PM
RE #22, & the quote from Hansen’s study, “The most direct GHG feedback is release of CO2 by the ocean due to temperature dependence of CO2 solubility and increased ocean mixing in a warmer climate that flushes the deep ocean of CO2 that accumulated through biologic and physical processes.”
When I read it I had in mind the frozen methane hydrates at the bottom of the ocean (from “biologic processes”). But I could be wrong. That’s what it seemed like to me with my limited understanding.
Also, do warmer oceans tend to turn the CH4 that is being released from the hydrates into CO2? And, if so, wouldn’t that be actually a bit better than the ocean releasing CH4 into the atmosphere where it is a much more potent GHG for the ~10 years until it decomposes into CO2.
Then, there is the issue to anoxic warming oceans turning this into hydrogen sulfide and poisoning life on earth. I imagine that might be a possibility in the distant future if we don’t mitigate GW enough. But that wouldn’t be a positive feedback, I don’t think, just a nasty effect of GW.
7 avril 2008 at 10:11 PM
I don’t know. Can you refute a man’s science if you can’t spell his name?
http://www.nature.com/ngeo/journal/v1/n4/full/ngeo157.html
8 avril 2008 at 12:01 AM
Just to clarify, are the figures being used in this post and Hansen et al C02 ppm, or C02 equivalent (GHG forcings)?
8 avril 2008 at 4:23 AM
I cannot at present see a major issue with Hansens analysis but I see big problem with politicians being able to swallow it. In recent talks I have seen him do he speaks of leaving coal in the ground or using CCS technology within a decade but looking at CCS technology it is either in development for new power plants or it has to be retrofitted at some point to existing power plants sooner which is unlikely to happen.
He then states that existing oil and gas reserves can be used so long as we leave unconventional oil alone. Anyone been to Athabasca recently? The oil sands there are being developed at a frantic pace, 1 mb/d now rising to 5 mb/d come 2020 and other shale and heavy oils are likely to be developed also once conventional oil begins to peak come 2015 as the head of shell announced recently.
If we really want to max out our Co2 levels at 450 ppmv (oil and gas usage only) then we has better really start compaigning now. I am sure that the world can do it but its just that lead times are so long for R&D, prototyping, and full commercial release that its doubtful that any significant dent in CO2 emissions can be made for 30 years.
8 avril 2008 at 4:55 AM
Gavin
I don’t understand Hansen’s assumption.
How conciliate the global temperature driving by CO2 and the lag between Antarctic temperature and CO2?
The initial “forcing” for glaciations isn’t, as you know, CO2, but regional summer insolation forcing, even if the global forcing is weak.
So can you explain, again, why Hansen considers only GHG in his sensitivity calculation?
8 avril 2008 at 6:10 AM
1) On a 6degC climate sensitivity in policy relevant timescales or not, having read this paper twice - I am very very unconvinced.
I’m still reading this para (Page 4) as a gaff:
“Paleoclimate data permit evaluation of long-term sensitivity to specified GHG change. We
only assume that the area of ice is a function of global temperature. Plotting GHG forcing (7)
from ice core data (27) against temperature shows that global climate sensitivity including the
slow surface albedo feedback is 1.5°C per W/m2 or 6°C for doubled CO2 (Fig. 2), twice as large
as the Charney fast-feedback sensitivity.”
I still see roughly equal contributions from GHG and ice sheet albedo (fig 1b), i.e. 1+1=2. And fig 2 after time=0, I see what is in effect a double count of forcing because the GHG alone seems to be equated with the full 3degC excursion, so because there aren’t the extensive ice sheets now 6 degC/2 = Charney’s ~3degC.
I still subscribe to a 3degC sensitvity, but am willing to be persuaded.
2) On SLR, since Hansen’s earlier paper where his team looked at the seasonal insolation peak correlations with ice-volume changes, I am now concerned (previously I didn’t count SLR as a major policy timescale threat). That’s especially the case given the Arctic and the potential for secondary impacts on Greenland and news from the Antarctic.
8 avril 2008 at 6:24 AM
Alastair #28
I asked William Connolley about this over at Stoat, as he modelled the impacts of the loss of Arctic sea ice a while back; his answer: “Well, it would lower the albedo, though perhaps not by as much as you might expect due to clouds and sun angle. Our study found little *long term* impact, because the ice largely regrew each winter. That included albedo effects.”
Hope that’s of interest.
8 avril 2008 at 6:58 AM
http://www.scientificblogging.com/news_releases/putting_the_west_antarctic_ice_sheet_in_proper_global_warming_context
This article appears to demonstrate that WAIS has been losing mass for a long time at around 2 cm per year but recently it has jumped to 1.6 M per year, a significant increase. And this is with only 0.8C of GW. With 0.6C in the pipeline from ocean latency and another 0.4 from existing infrastructure already in place I really fear for the ice sheets flow rates into the oceans. If we are releasing GHG’s at 30x any known historical rate and 1.6 M become 2 or 2.5 M per year then things are only going to accelerate for the next 60 years at least even if we stop all CO2 emissions significantly in 20 years time.
8 avril 2008 at 7:18 AM
Just so I’m sure I understand, it seems you’re basically saying that the “resting state” of climate in the long run after doubling of pre-industrial CO2 is likely warmer than the shorter-term (100 years or so) response of the system. But you’re also saying that uncertainties in feedbacks etc are very large (perhaps an understatement, actually).
That would seem to leave high long-term sensitivity in the realm of what Princeton’s Steve Pacala has called “the monsters behind the door” — possible, but not necessarily clear threats. That’s different than coming to a conclusion that 350 ppm is an appropriate long-term limit for CO2.
For us non-scientists, does this question, because of the uncertainties, still rest in that simple precautionary place (”do no harm”) or has this paper truly narrowed the scope of what’s possible from the human greenhouse intervention?
[Response: The key point to take home from this study is that the initiation of glaciation likely didn’t happen at 550 ppm or 650 ppm or similar - it was likely less. That implies that if you wait long enough with levels that high, large scale glaciation is probably unsustainable. Undefined in all of this is what ‘long enough’ means, and whether you can get a better lower bound. Those are unfortunately exactly the issues that matter in the short term. I think that it is difficult to rule out definitively that it is as low as 425 ppm or so. However, as I stated above, initial targets that are being set now are not set in stone and are not yet really being worked towards. So does this add to pressure to move ahead on emission reductions? Yes, but there is no shortage of reasons to be working on that already. - gavin]
[Response: We should also recall the implications of Dave Archer’s “long tail” of anthropogenic CO2. Something like 20% of the anthropogenic CO2 will stick around for much more than 1000 years. That tells us something about how much peak CO2 we can tolerate without committing the planet to extreme consequence of the very long term warming. For example, if we reached a peak CO2 of 1200 ppm, then the long term tail contains about 280 + (1200-280)/5 or 464 ppm CO2. That would mean that even if the deglaciation took a very long time to set in, the CO2 would indeed stay above the threshold level for a long time. This is only a crude illustrative calculation, and to do it right would take a proper ocean carbon cycle model, but I hope it gives the idea of what Hansen’s calculation implies even if the catastrophic changes require a very long time to act. –raypierre]
[Response: I’m very pleased I can disagree with Gavin for once (this is hard). The CO2 level at which glaciation started (in a phase of declining CO2 concentration) is very likely not the same as the CO2 level where the ice sheets will vanish again (in a situation of rising CO2 concentration) - the latter very likely is quite a bit higher. This is because of the positive ice albedo feedback which leads to hysteresis - the basic concept is well known since way back (I think Budyko) and this is also found in coupled climate - ice sheet models like our CLIMBER-2 model - see Calov and Ganopolski 2005. -stefan]
8 avril 2008 at 8:26 AM
I would like to look at this statement from the Hansen paper:
The calculation above is for a long period of time and includes all the slow feedbacks, so I do not know why Hansen calls it a fast feedback. Since the greenhouse gas portion is about half of the total forcing (ie. 1 + 1 = 2), if you consider them the cause (or at least the main feedback) then you get a GHG sensitivity of about 6 degrees. With ice sheets pushing below 45 degrees of latitude, this looks close to a snowball-Earth condition which has a high climate sensitivity. Luckily the same thing was not also happening in Asia, or we might no be here to write about it. A look at the increasing temperature response to the same orbital forcings as average temperature dropped shows that climate sensitivity became significantly larger during the Pleistocene ice ages.
I am surprised that Hansen did not use the Pliocene (about 3 million years ago) as a benchmark. Here we have CO2 levels around 400 ppm, global average temperature about 2 or 3 degrees higher, and sea levels 25 to 35 meters higher (think ten story building). The carbon dioxide forcing is about the same ( 280 ppm Interglacial / 180 ppm LGM is close to 400 ppm Pliocene / 280 ppm Interglacial ) for a temperature change about half as much, implying a much lower climate sensitivity, closer to three degrees rather than six for the period we are about to enter.
I still do not think you can use the temperature (or CO2 level) for the initiation of glaciation to be the same as that sufficient to melt the ice cap. For a large continent like Antarctica I think it will take a few extra degrees to overcome the thermal inertial of all that ice, unless someone can demonstrate why this is wrong.
8 avril 2008 at 9:28 AM
#22 Blair Dowden,
This might help:
“Carbon dioxide is more soluble in cold water, so at high latitudes where surface cooling occurs, carbon dioxide laden water sinks to the deep ocean and becomes part of the deep ocean circulation “conveyor belt”, where it stays for hundreds of years. Eventually mixing brings the water back to the surface at the opposite end of the conveyor belt in regions distant from where the carbon dioxide was first absorbed, e.g., the tropics. In the tropical regions, warm waters cannot retain as much carbon dioxide and carbon dioxide is transferred back into the atmosphere” http://science.hq.nasa.gov/oceans/system/carbon.html
Scroll down to the first bullet point.
With regards stronger winds in a warming planet, see Toggweiler & Russell “Ocean Circulation in a Warming Climate.” Nature 17/1/08. That suggests a role for vertical temperature gradients in strengthening winds, such vertical gradients should increase with more global warming. Therefore regionally stronger winds could occur, and in the Southern Ocean that can impact overturning/mixing through Ekman Transport, the Southern Ocean is big! (I wonder if such enhanced wind driven mising would in effect be a negative feedback on warming rates, enhaning ocean thermal damping.)
#32 George Darroch,
Where people don’t put units, you can safely assume that if the figure’s in the hundreds it’s probably atmospheric concentration in parts per million, where it’s below or around 10 it’s probably Watts per square metre.Otherwise concentration is “ppm” and forcing “Wm2″.
#34 Pascal,
Why not read the actual paper?
Hansen’s team explain why they consider CO2 to be reasonably considered the primary forcing where they do so. But they also consider the other primary forcing as albedo changes.
#36 Outeast, thanks for that.
8 avril 2008 at 10:31 AM
Andy Revkin, think about doubling times in other areas. Pondweed on a lake. Mussels in cooling water intakes. Scum in a clean water system. Radiation in a fission pile. Epidemic spread compared to background existence of a pathogen.
Those are all simple compared to climate. All are places where increasing some kind of moderating influence early on prevents a world of trouble by impacting the doubling time, lessening or halting the growth of the problem.
We have lots of experience with this. We know we don’t notice problems until it’s almost too late — and the more profitable the system externalizing a cost, the more pressure not to notice those costs.
This might be our final examination.
8 avril 2008 at 11:02 AM
Antarctica has been glaciated several different periods over the last 600 million years. It didn’t just start 34 million years ago, that is just the start of the latest episode of glaciation.
Antarctica was likely glaciated 580 million years ago, 450 million years ago, 300 million years ago and 150 million years ago. CO2 levels could have been as high 3000 ppm to 5000 ppm in some of those different periods.
Antarctica is an unusual case in plate techtonics since continental drift has placed Antarctica around the south pole for most of the past 600 million years including various times when it was locked together with other continental plates.
So, I don’t think the 6.0C sensitivity estimate is robust throughout the entire geologic record.
8 avril 2008 at 11:59 AM
#40 Coblyworlds
If you say:
“Hansen’s team explain why they consider CO2 to be reasonably considered the primary forcing where they do so. But they also consider the other primary forcing as albedo changes.”
there is 2 forcings and their sum is 3.5 + 3.0W/m2 = 6.5W/m2
so the sensitivity is 5°C/6.5W/m2 = about 0.75 °C.m2/W
No, Hansen consider CO2 forcing alone, to find about 1.5°C.m2/W.
My question was: why to consider CO2 alone?
But I think Hansen uses the particuliar case of glaciation to know the impact of ice-sheet as a slow feedback.
He assumes in his paper that ice-sheet feedback depends only of temperature and global forcing.
And the alone real global forcing is GHG, even in the case of Pleiostene.
This is what I understand now.
8 avril 2008 at 1:09 PM
from Gavin’s article:
“… it is clear that from the Pliocene to the Quaternary … the climate has become more sensitive to orbital forcing. It is therefore conceivable (but not proven) that any sensitivity derived from paleo-climate will not (in the end) apply to the future.”
This statement seems to permit opposite interpretations:
1) The earth has gradually become more sensitive to orbital forcings. This could indicate a greater overall sensitivity, and thus a tendency for paleoclimate-based projections to underestimate the current sensitivity.
2) Because the earth is more sensitive to orbital forcings, and because orbital forcings are headed in the cooler direction, paleoclimate-based projections could overestimate the sum of forcings we’re likely to experience.
Are either or both of these readings in error?
8 avril 2008 at 1:40 PM
Andy (#38),
I think the the precautionary level is 280 ppm. What this preprint (and it is a preprint, not a paper) is arguing is that the sensitivity is larger than has been assumed up until now and so a “safe” temperature (a la Exeter) corresponds to a lower concentration (350 rather than 450). It does so so much that a scenario is developed to show how 350 ppm might be achieved (fig. 6). So, the preprint takes the risk quite seriously. We don’t know what it will be once it is a paper. Hansen has a habit of being right, but there may be some flaw in the analysis that a referee catches.
To some extent, the argument has already been published in Pilosophical Transactions. There is more detail here though.
Gavin (also #38),
I think that we are working up to meeting targets. Some countries will meet Kyoto compliance, though if they do this through biofuels, this will be a mirage. So, there is some progress. Your point that all we need to know for sure right now is the direction (emissions cuts) makes some sense, but the manner in which we cut emissions might be influenced by the present work. Greater efficiency cuts emissions, but it does not leave energy to do sequestration while shifting energy sources might make a difference. Solar power is expected to be cheaper than coal in less than a decade, but biochar may never be as an energy source. Yet, we might start planning to absorb the opportunity cost and promote biochar production in order to make progress on sequstration even though it might slow emissions cuts a little. Right now, that would mean supporting research into biochar, its effectiveness in sequestration and its utility as an energy source.
8 avril 2008 at 2:40 PM
#43 Pascal,
Sorry, I had thought you were talking about the Cenozoic.
I think Hansen is only fixing on CO2 because that is the major issue the paper addresses. There are statements throughout the paper about other mainly albedo based changes, and there’s reference to methane with regards the PETM (page25).
#44 Daniel Goodwin
The variation in climate sensitivity could in theory be higher or lower. From what I read (and I am only an amateur) orbital forcings are too slow to be a factor in sub-centennial processes. Orbital factors can initiate, but the insolation rate of change due to orbital factors would not drive the detailed processes at a centennial scale (Dansgaard Oeschger etc).
As an aside:
Hansen’s earlier paper “Climate change and trace gases” refers to the spring as a key factor in melt, page 8 under figure 3. http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_2.html Then proceeds to outline the claim that ice-sheet melt is actually a rapid process.
In Gerard Roe’s “In Defence of Milankovitch”, http://earthweb.ess.washington.edu/roe/Publications/MilanDefense_GRL.pdf he shows that the rate of change of global ice volume tracks beautifully with 65degN insolation.
Hansen’s team have been building up a case that ice-sheet loss is in fact a relatively rapid process so is relevant to policy timescales. I think they have a strong point on this, but am still not convinced about this 6degC sensitivity. I’ll butt out and see what others have to say.
8 avril 2008 at 4:26 PM
Blair, I would guess that the last glacial maximum, LGM, some 19-30 kyr ago, was chosen instead of the Pliocene, 3 million years ago, because there is a lot more data on conditions during the LGM (no ice core measurements from the Pliocene, for example).
The whole notion of the surface temperature response to 2X CO2 climate sensitivity as the main publicly discussed benchmark seems misleading, however. It was originally just a climate model benchmark, wasn’t it? Mostly for the convenience of modelers when comparing their different models.
An equally important variable is the ocean temperature response to increased CO2, which has suffered from large uncertainties. According to Levitus et al (GRL 2004):
Compare this to a more dated estimate (Science 2000):
That is a large change in estimates. A number like 0.06C might seem tiny, but it represents far more energy storage in the oceans than a 0.6C increase in the surface temperature field. So, what’s the current best estimate of the ocean temperature sensitivity? What’s the best estimate of the amount of heat the oceans have absorbed?
Based on the evidence in polar regions, where warming rates and ice melt rates have outstripped model predictions, (not much net albedo change yet, is there?), it seems that polewards heat transport by oceans (and atmosphere) might be accelerating the rate of response (not the equilibrium response, but the rate of approach to equilibrium).
This from Levitus 2001:
So, if that’s correct, the ocean is what we want to watch. If we had launched the Triana/DSCOVR climate satellite ten years ago, instead of mothballing it, we’d probably have robust answers to the energy budget question, and we could get the ocean heat change by calculating the (total energy change)-(atmospheric warming).
Regarding the “monsters in the box”, what that points to is the “labile carbon store” which is currently in soils, sediments, and permafrost: the carbon in the freezer. Warm up the freezer, and all of a sudden microbes can start converting it all to CO2, H2S, etc. Stinky. Obviously the biosphere will play a huge role in that - but we shouldn’t expect the biosphere to absorb that excess carbon. It seems that during stable climate periods the biosphere operates mostly in steady state, pushing 100 gigatons of carbon through the system each year via photosynthesis and respiration, but in balance. That’s the big looming issue.
8 avril 2008 at 4:53 PM
RE #36 & “Our study found little *long term* impact, because the ice largely regrew each winter. That included albedo effects.”
I’ve sort of always thought (reducing) albedo might not be much of a long term issue, esp once all the ice/snow is melted.
However, it seems to me that ice forming in winter in the Arctic wouldn’t have a tremendous +albedo (cooling) effect either, since there’s not as much sun up there in the winter as in the summer. OTOH, I think that the sun’s energy gets used up a lot in the melting process of that ice each summer, rather than in warming the planet, so if there were no or little ice formation in the winter and not much to melt in the summer, that would have an impact (like a jump up in temp). Not a continual one, once equilibrium is reached.
I’d think its the lesser or greater ice cover during those long summer days that would should the greater albedo effect.
8 avril 2008 at 5:01 PM
Albedo is the one thing we will have great control over in the future, with the 10 billion people all wanting a modern and comfortable lifestyle. That’s going to take a lot of solar panels and other two dimensional surfaces, in fact, combining agriculture, land use and biodiversity preservation, one can make the assumption that it is going to take ALL of the available surfaces. Here is where material science and condensed matter physics again comes into play - these surfaces can be exceeding thin, and they can be engineered to either be reflective, transparent, transmissive or emissive, with an electronically controlled and very fast response times.
Work that into your global models. We need a very large area for energy anyways, and if you add up the dead areas we have created already, there’s plenty of room here.
8 avril 2008 at 5:54 PM
Re #49 solar power would not take all that much space. A concentrated solar system in desert area 250km by 250km would supply all the Worlds current electricity demands.
8 avril 2008 at 5:57 PM
Since Hansen’s latest estimate is bound to arouse controversy, I’ve posted a revised graphic precis of past sensitivity estimates- Levenson’s 2006 compilation did not include Arrhenius second thoughts, published a decade after he produced the Victorian estimate that set the roller coaster in motion:
http://adamant.typepad.com/seitz/2008/04/target-of-fear.html
8 avril 2008 at 5:59 PM
Re #36 where outeast wrote:
“… William Connolley … modelled the impacts of the loss of Arctic sea ice … “Well, it would lower the albedo, though perhaps not by as much as you might expect due to clouds and sun angle. Our study found little *long term* impact, because the ice largely regrew each winter. That included albedo effects.”
Hope that’s of interest.”
It is interesting but not surprising. It sounds as though Connolley limited the SST to -1C and so a major positive feedback from the greenhouse effect of water vapour would have be suppressed. Moreover, as CEP Brooks explained, it is highly unlikely that the sea ice will reform in winter if there is no multi-year ice there to provide a surface where the air can be cooled well below the freezing point of sea water.
Moreover, he was using an atmosphere only model, and even the full Ocean-Atmosphere model cannot replicate the melting Arctic ice. Vellinga and Wood (2002) had already tried to replicate the rapid warming at the end to the Younger Dryas with that model but its forcing was insufficient.
The problem is that the modellers are using the wrong paradigm! See http://www.realclimate.org/index.php/archives/2008/04/target-co2/index.php?p=509#comment-84027
I think I would rather take Hansen and Broeckers ideas than Connolley. Broecker believes that sea ice caused the Younger Dryas http://www.amnh.org/sciencebulletins/earth/f/glaciers.20050331/essays/59_1.php
and Hansen believes that albedo is the main forcing. So although I am interested to hear of Connolley’s work I am far from convinced that loss of the Arctic sea ice will not lead to disaster
8 avril 2008 at 7:04 PM
A concentrated solar system in desert area 250km by 250km would supply all the Worlds current electricity demands.
Ok, fair enough. Now simulate what the local effects of such a large array would be when going to the reflective, the black to transparent state on nanosecond time scales.
Such will be the state of condensed matter physics very shortly. If we can do that locally, we should be able to do it globally. Not only does that solve the power problem, but that also solves the thermostatic problems.
8 avril 2008 at 8:05 PM
Re #40: Thanks for the Toggweiler & Russell paper. I had not realized the importance of the increasing vertical temperature gradient on wind speeds. One would expect a different global wind (and ocean current) pattern than the current one driven by the polar-equator temperature difference. This could have important effects on some regional climates.
However, I think increased ocean circulation would reduce CO2 levels by removing it from the atmosphere faster than it can be returned on the other end of the cycle. The deep ocean is presumably under saturated relative to the high atmospheric CO2 levels of today and the future, and would therefore absorb some of the CO2. So I still do not fully understand Hansen’s statement that I quoted.
My main problems with the Hansen paper remain:
1) I think he is extrapolating a high glacial era climate sensitivity into that for a warmer climate where it will be significantly less.
2) He is using the conditions for ice sheet formation as the criteria for ice sheet melting, not taking the thermal inertia of the ice sheet into account.
[Response: Regarding your second point, you are confusing thermal inertia with hysteresis. The thermal inertia of the ice sheets says that to deglaciate, the warming must persist for a sufficiently long time. As Gavin notes, it is uncertain how long “long” is, but it’s probably a good bit more than a century. Hysteresis, on the other hand, would say that no matter how long you wait, the deglaciation happens at a lower CO2 threshold than the initiation, since the ice sheet creates conditions that tend to maintain itself. Rob DeConto’s work shows there is some hysteresis in this problem, but not much, when Milankovic effects are taken into account. In fact, if the initiation happened during Milankovic conditions that are favorable to glaciation, while you increase CO2 at a time that’s favorable for deglaciation, the deglaciation could well happen at a lower CO2 level than the initiation (though that’s not a case Rob computed explicitly). –raypierre]
8 avril 2008 at 8:09 PM
For anyone who’s more or less convinced by Hansen, please join us at 350.org. Our slightly insane goal is to make 350 the most well-known number on the planet in the next 18 months. We need artists and musicians and political organizers (on Saturday 350 bicyclists rode in circles in Salt Lake City). It’s not completely insane, either–our team organized 1400 rallies in all 50 states last April for domestic climate action. Now we’re just trying to do it for the, you know, whole planet
For my money, Hansen’s paper is the most important development in the climate debate since the IPCC 1995 report. I think it’s going to turn out to be our last real shot at turning public opinion, and with it political action, away from incremental change and towards transformative action. Many thanks to realclimate for keeping us all apprised, and please join us at 350.org
8 avril 2008 at 10:46 PM
Re # 29 Jim Bullis: “…why would CO2 solubility decrease if surface water warmed slightly and deeper water warmed more?”
Because CO2 solubility is inversely related to temperature (http://jcbmac.chem.brown.edu/myl/hen/carbondioxideHenry.html)
8 avril 2008 at 10:51 PM
53:
If we are using solar power, then at least for the active wavelength of the device(s) we will have high absorption, i.e. panels will have very low albedo. The best way to mitigate this is to decrease overall energy demand, and increase the PV efficiency. Max efficiency today is around 40%. But current human energy needs are roughly 1 part in 10,000 of insolation, so even at 10% efficiency we are only increasing solar heat absorbed at the surface by .1%.
But the larger point, that our species controls a substantial surface area of the planet, and perhaps if albedo management were made a priority, we could provide sufficient negative shortwave forcing by this means? For affecting the earths climate system, there is no need for short time scale albedo changes. Of course in a science fiction sense, coupling a weather model, with the ability to rapidly control the albedo of a significant part of the earths surface would allow some degree of control over the weather.
Some other comments, for the experts to reply, as I’m not capable of properly evaluating:
regarding paleoclimate icesheet decay rates: it can be argued that Northern ice sheets were highly vulnerable to collapse into the sea, i.e. a significant chunk of the Laurentide was grounded over Hudsons bay, and also major parts of the European over the North Sea? GIS does not seem to possess this sort of vulnerability to rapid collapse, although the WAIS might be vulnerable. Another thing I don’t hear discussed is how the albedo of a melting part of an ice sheet might evolve over time. If buried dust accumulates on the surface of the ice as it melts (this is common in Alpine glaciers, which are very much dirtier in general -and probably have larger dust particles) how low might the summertime albedo become?
I was unconvinced by Connolley’s ice free arctic summer runs. I think he treated the ice/ocean as a fixed boundary condition for the GCM. I would think that the greatest energy anomaly would be the increased solar absorption, which is largely absorbed by the ocean. Some of this heat will be “liberated”, by the later freezeup in the fall. But probably more importantly the incremental heat would likely be transported deeper into the ocean. I suspect it would take decades for this change in oceanic circulation to have much of a global impact.
8 avril 2008 at 11:59 PM
Re #53: I’m not sure what you’re trying to get to with that question. An actual 250km x 250km solution wouldn’t work for myriad reasons, so trying to figure out what good or bad things would happen with it are pointless.
Re #45: What sequestration points to is that we have to stop recycling anything that contains carbon and comes from renewable sources. We also need to come up with the Backyard Carbonizer, that can replace the trashcan and recycle bin as the disposal place of first resort. A small parabolic reflector pointed at the bottom of a large cast iron pot should reduce most carbon based rubbish to carbon in short order. Better yet, get those thermal depolymerization guys rolling out their plants faster.
9 avril 2008 at 3:59 AM
Re #42, I believe it is in relation to where Antartica is today, ie the south pole. 600 million years ago, it did not exist officially and probably not 300.150 million years ago either. Plate tectonics and all that.
9 avril 2008 at 4:36 AM
http://video.google.co.uk/videoplay?docid=9171659355384722877&q=james+hansen&total=186&start=0&num=10&so=0&type=search&plindex=1
If we just use all of the conventional oil and gas reserves we will hit 450 ppmv of CO2 and risk a different planet. James Hansen.
9 avril 2008 at 5:56 AM
RE #54: I think there is a major component of hysteresis just due to the thickness of the East Antarctic ice. Melting starts only when the temperature at the surface altitude of 3 km rises above 0 degC for some substantial time each year.
I believe a balmy summer day there means presently about -15 degC. A 6 degC rise in global average might just about cause some surface melting at that altitude because of polar amplification. Maybe this is one of the tipping points.
Return of the ice cover will start on the bare ground at a low altitude and will then require lower global average temp conditions.
Greenland and Western Antarctica are likely to melt first precisely because of their low altitude surfaces.
9 avril 2008 at 6:37 AM
Russell Seitz posts:
[[Since Hansen’s latest estimate is bound to arouse controversy, I’ve posted a revised graphic precis of past sensitivity estimates- Levenson’s 2006 compilation did not include Arrhenius second thoughts, published a decade after he produced the Victorian estimate that set the roller coaster in motion:]]
I note that you have Hansen’s estimate as the final one. Did you miss the repeated notice that that was a long-term sensitivity and not a short-term sensitivity? Apples and oranges, buddy.
9 avril 2008 at 8:01 AM
After reading the paper, I note it is interesting that the only CO2 proxies around the 34 million year ago Antarctic glaciation period are in fact …
… 1500 ppm (not 450 ppm) ???
The only references within 10 million years of the period are from Pagani et al 2005 (1,500 ppm +/- 500 ppm) and Retallic 2001 (1,000 ppm +/- 500ppm).
9 avril 2008 at 8:49 AM
Possibly of relevance to this discussion:
Stanford Report, April 2, 2008
Phytoplankton species deviates from norm: No CO2 absorbed in photosynthesis-
Findings could affect scientists understanding of amount of carbon dioxide phytoplankton pull from atmosphere
A widespread species of ocean-dwelling microorganisms has been found to employ a never-before-seen alternative method of photosynthesis…The discovery has implications not only for scientists’ basic understanding of photosynthesis—arguably the most important biological process on Earth—but also for the amount of carbon dioxide that phytoplankton pull from the atmosphere….
“There is a new twist on photosynthesis here, and that has to be accounted for when it comes to CO2 modeling,” Bailey said, adding that, in some cases, the models may overestimate the amount of carbon fixation that occurs in nutrient-poor waters.
It is not yet clear what the finding might mean to studies of long-term global warming, he said, but it will have to be incorporated into any models that include carbon fixing by phytoplankton as a factor…
http://news-service.stanford.edu/news/2008/april2/plant-040208.html
9 avril 2008 at 9:07 AM
Isn’t the question of a “target CO2″ level moot, given that anthropogenic CO2 emissions are not only increasing every year, but accelerating, and all indications are that global fossil fuel use and associated emissions will continue to increase for years or decades before they peak and begin to decline?
The “target” that really matters is the year in which global CO2 emissions will be less than the previous year and will thereafter rapidly decline to near zero. It seems implausible that humanity will achieve that “target” in time to prevent catastrophic warming and climate change.
9 avril 2008 at 10:30 AM
Re #53 when I say 250km by 250km that’s just the total area. They do not all have to be in the same piece of desert. They can be scattered in smaller units if need be.
9 avril 2008 at 10:33 AM
Re #47 Ike. According to James Annan the number for ocean heat content rise in the Levitus Science 2000 paper was an arithmetic error, see end of http://julesandjames.blogspot.com/2008/04/frogs-and-blogs.html
Otherwise I agree that ocean warming is a key issue, but its now problematic in that Argo is not showing any warming since 2004 while the combination of Jason and Grace finds the warming to be continuing at the same rate as earlier. The latest presentation on this issue is here http://ibis.grdl.noaa.gov/~leuliett/presentations/osm_2008.pdf
9 avril 2008 at 10:49 AM
It seems implausible that humanity will achieve that “target” in time to prevent catastrophic warming and climate change.
In 1908 it seemed implausible that one could step onto a modern jetliner and fly anywhere in the world, or that man could walk on the moon. There was this one guy, Konstantin Tsiolkovsky who thought it might be possible.
The fact that now people understand that not only do we need to reduce carbon output to zero, but we have to remediate the atmosphere back to a previous CO2 level, is the first step. If we can do that, 300 or 320 ppm is just as reasonable, indeed, most people studying the problem understand that 350 is probably the upper limit. Hansen et al. have merely quantified it to the best of their abilities, and within the state of the art of science.
You’re on a spaceship, carbon dioxide is increasing, you know you have a problem, yet you continue to breathe. Breathing is necessary to solve that problem that you know exists, and you know you do have to solve it.
There is of course a time limit with this problem.
Anyone that now claims there isn’t a problem to be solved have been adequately warned, and the minimum bar is set.
Good luck! On this post I linked to my blog. I don’t come in here much, only when something of significance happens or is published. Hansen again has risen to the challenge.
9 avril 2008 at 10:59 AM
We’re doomed. Move inland
9 avril 2008 at 11:21 AM
> moot
Nope. Else we’d be living with whatever level of pollution industry gave us at their high points.
You never know what is enough until you know what is more than enough.
9 avril 2008 at 12:04 PM
Re Raypierre’s response to #54: Thank you for clarifying the difference between thermal inertia and hysteresis. Orbital forcings are obviously critical to the formation of the Laurentian Ice Sheet, but on the timescale of the ice sheets of Antarctica and Greenland, would they not just be noise in the average temperature signal?
I am trying to get a feel for how much hysteresis there is in the Antarctic ice sheet. Three million years ago CO2 was at 400ppm, temperatures were 2 or 3 degrees higher and sea level was about 30 meters higher. Since CO2 is now almost 400ppm, does it follow that if it stays at that level we will get 30 meters, or is it more like 15, 20 or 25?
9 avril 2008 at 2:09 PM
What I get from this latest paper on estimating a climate sensititivity factor is that it’s a moving target.It reinforces the fact that there are many un-certainties involved. Feedback parameters are complex in their relationships.
Increasing surface temperature increases evaporation and adds to atmospheric H2O which is a greenhouse gas that adds to temperature rise, but this can also increase cloud cover which increases albedo which has a cooling effect and leads to temperature decrease. Go figure! It’s a problem, and must add to the headaches already confronting climate modelers.
9 avril 2008 at 2:35 PM
#54 Blair Dowden,
I agree that at first glance it might seem that increased overturning should increase CO2 uptake because of high current CO2 levels, but the deeps actually have high concentrations of CO2.
Have you read David Archer’s post on reduced ocean uptake? http://www.realclimate.org/index.php/archives/2007/11/is-the-ocean-carbon-sink-sinking/
specifically 5th para down.
It would have been better for me to have linked to it earlier, but I got distracted and forgot. Sorry.
9 avril 2008 at 5:07 PM
One thing a poster mentioned is the location of Antarctica. While all the other continents have shifted position over millions of years Antartica doesn’t seem to have moved at all from the South Pole. Is there a reason for this?
9 avril 2008 at 8:25 PM
Re #73: CobblyWorlds, thanks, I read that article but I guess it did not sink in (pardon the pun). The idea is that the deep ocean has excess carbon dioxide because of decaying organic matter. The present ocean circulation is not sufficient to recycle it back to the atmosphere quickly enough. But I have just learned that wind speeds, and presumably ocean circulation, are higher with warmer temperatures. Therefore CO2 must have been building up in the deep ocean for millions of years. If that rate is not very slow there must be a large imbalance.
As is often the case, I get a piece of information, but not the whole picture. I hope someone can make sense of it for me.
9 avril 2008 at 9:44 PM
Here is my picture of the global wind - ocean current system. There are two main sources of atmospheric circulation. The horizontal gradient (temperature difference between equator and poles) decreases with increasing global temperature, while the vertical gradient increases. It is not clear which one is stronger. Ocean circulation depends on wind strength, although maybe the vertical gradient is more effective. Ocean circulation appears to have been weaker at the last glacial maximum. This would suggest that increasing greenhouse gases will increase ocean circulation. But in the Cretaceous, when CO2 levels were very high, the ocean circulation was so weak that the ocean became stratified, and led to ocean anoxic events where the lower levels had no oxygen. There is a piece of the puzzle missing here.
9 avril 2008 at 10:09 PM
> deep ocean
Blair, I’d be real curious to know the sources for any actual observations — since there are a fair number of photographs of whale skeletons on the deep ocean floor, that suggests there’s not enough CO2 dissolved there to make the pH effective at dissolving bone, so I’d wonder where measurements were taken.
There are a few, for example this fascinating observation:
http://www.pnas.org/cgi/content/full/103/38/13903
Lakes of liquid CO2 in the deep sea
(footnotes there all worth following)
But that’s associated with a hydrothermal system, not decaying material.
10 avril 2008 at 12:29 AM
Is not often that Dr Gavin Schmidt is wrong about something with respect to climate. But I just learned that he failed on his prediction that world wide warmer temperatures will come back at year end.
They will not, It came back full force in March just past with a staggering +1.4 C anomaly for the Northern Hemisphere. http://data.giss.nasa.gov/gistemp/ . My respect for Gavin as a tireless advocate of good climate is however not lowered at all, he taught many of us about sensitivity, and so we shall remember that temperatures are not so hard to predict , with sensitivity in mind there can be variances….
10 avril 2008 at 1:53 AM
Re: #73: D Price Says: “One thing a poster mentioned is the location of Antarctica. While all the other continents have shifted position over millions of years Antartica doesn’t seem to have moved at all from the South Pole. Is there a reason for this?”
I think you are referring to what John Lang wrote in #42: “Antarctica is an unusual case in plate techtonics since continental drift has placed Antarctica around the south pole for most of the past 600 million years including various times when it was locked together with other continental plates.”
Unless I am missing something, I thought much of what became Antarctica was equatorial from the Neoproterozoic Era until sometime after Gondwana drifted southward (late Ordovician). It wasn’t until the Mesozoic that Antarctica made its way down to the south pole (about 140my).
10 avril 2008 at 4:02 AM
Re #74 where D Price ask why Antarctica has not moved.
I have never seen a a reason given, but then I have not seen that question asked before.
My own idea is that it is due to centrifugal/centripetal forces. Because Antarctica is centred on the South Pole the centripetal forces cancel each other out. India, on the other hand, moved away from the region of the Southern Ocean and was accelerated as it approached the equator. That acquired momentum has resulted in it crashing into Asia and building the Himalayas.
Cheers, Alastair.
10 avril 2008 at 4:32 AM
Re D Price
The thought is essentially incorrect. However, it hasn’t moved much compared with how far the other continents have moved since ~90 Mya though. See the powerpoint animation on the linked page.
It seems to me (possibly wrongly, since tectonics isn’t my bag) that the movement of the other continents has constrained Antarctica’s movement over that last period.
10 avril 2008 at 5:26 AM
raypierre
you say:
“[Response: We should also recall the implications of Dave Archer’s “long tail” of anthropogenic CO2. Something like 20% of the anthropogenic CO2 will stick around for much more than 1000 years. That tells us something about how much peak CO2 we can tolerate without committing the planet to extreme consequence of the very long term warming. For example, if we reached a peak CO2 of 1200 ppm, then the long term tail contains about 280 + (1200-280)/5 or 464 ppm CO2. That would mean that even if the deglaciation took a very long time to set in, the CO2 would indeed stay above the threshold level for a long time. This is only a crude illustrative calculation, and to do it right would take a proper ocean carbon cycle model, but I hope it gives the idea of what Hansen’s calculation implies even if the catastrophic changes require a very long time to act. –raypierre]”
this is logical.
But Hansen’s calculation gives us a CO2 target at 350ppm.
If I use your equation, I find a short term target at 630 ppm to get a 350 ppm tail.
If I use 450ppm now, we get without problem, a 314 ppm tail.
So why 350 ppm now or in few decades?
Because 314 ppm is a dangerous concentration?
I understand that the phenomenons are non-linear, but we know that a long time ago.
So what is the deep interest of this new Hansen’s article?
10 avril 2008 at 6:46 AM
hum
following my precedent post.
314ppm implies 5.3 ln(314/280) = 0.607W/m2 forcing.
even with 1.5°C.m2/W temperature increase is, “only”, 0.9°C since preindustrial age, close to today increase.
It’s very surprising that such a minor temperature anomaly is so dangerous.
10 avril 2008 at 8:52 AM
Blair, The deep oceans are quite isolated from the surface. The water is colder, saltier and denser. CO2 dissolves more readily under pressure and at low temperature, and this further increases density and stratification. In the very deep ocean, CO2, CH4 and H2O condens out and form clathrates. I’ve had friends on submarines, and they confirm that even in a hurricane, things are very quiet in deep water. You hear about damage to drilling platforms and pipes, etc. What people forget is that that is all pretty shallow. The ocean is another world.
10 avril 2008 at 9:22 AM
The value of climate sensitivity should inform important economic and political decisions. As a decision tool, Hansen’s more conservative value may be a more prudent and wiser value to use than a lower value, which might be more consistent with the body of atmospheric science.
The value we select will affect how we deal with climate warming. A larger number says that, “Now, we must act more aggressively!” A smaller number says,”We can procrastinate and survive.”
If we pick a larger number, and act now, later we can say, “Oh, the actual climate sensitive number is a littler smaller.” If we pick a smaller number, and thereby fail to act in time, there will be no later. Hansen’s larger value is more prudent.
The kind of Arctic Sea Ice retreat that we have had over the last 3 years, was predicted by the IPCC models not to occur for another 40 years. If the IPCC says 40, and the correct answer is 4 years, then we cannot do engineering based directly on the IPCC predictions and projections. We must incorporate safety factors of 100 or 1,000, or even a 100,000 where large populations are at risk. Even Hansen’s number may not include a sufficient safety margin for direct use as an engineering basis of design where large numbers of people are at risk.
Our climate sensitivity number is not merely a matter of what can be defended in a publication; it is a matter of what the wise policy is.
10 avril 2008 at 10:08 AM
It is interesting to note that Dr Hansens new work suggesting an increased climate sensivivity of limiting GHG emissions to no higher than 450 CO2e which corresponds to a average temperature increase of less than 2C (high probability) means that he is taking the stance (politically) that we can use all of the conventional oil and gas but must leave the coal in the ground.
Coal is not being left in the ground just as unconventional oil sources arn’t either. Oil is currently fetching $110 a barrel on the open world market and that is making people want to produce more of it inline with global economic growth of between 2% and 3% per annum. CTL is coming online this year outside of south africa, China, Indiam, USA etc all have projects of this nature and come 2020 a billion barrels a year could be coming from this source. The Athabasca tar sands are also going to end up supply around 1.5 to 2 billion barrels a day come 2020. As conventional oil surges in price due to the effects of peak so do alternative oil sources come online from fossil fuel sources. This is why we must have a biofuel solution that takes oil away in order to have any chance of not reaching 450 CO2e in record time.
New coal fired power plants are coming online to without CCS at the present time, retrofitted by 2020, lets hope so but it is a tall order.
James Hansen just seems to of reduced our chances of limiting sea rise and atmospheric warming somewhat.
10 avril 2008 at 10:18 AM
I have a question:
How confident are we that the the Co2-temperature lag is ~800 years?
My understanding is that it is difficult to estimate the ice age-gas age difference in ice core records. I have found a recent article that is suggesting that the 800 years lag is maybe overestimated.
http://www.clim-past.net/3/527/2007/cp-3-527-2007