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Ocean heat storage: a particularly lousy policy target + Update

Filed under: — stefan @ 20 October 2014

The New York Times, 12 December 2027: After 12 years of debate and negotiation, kicked off in Paris in 2015, world leaders have finally agreed to ditch the goal of limiting global warming to below 2 °C. Instead, they have agreed to the new goal of limiting global ocean heat content to 1024 Joules. The decision was widely welcomed by the science and policy communities as a great step forward. “In the past, the 2 °C goal has allowed some governments to pretend that they are taking serious action to mitigate global warming, when in reality they have achieved almost nothing. I’m sure that this can’t happen again with the new 1024 Joules goal”, said David Victor, a professor of international relations who originally proposed this change back in 2014. And an unnamed senior EU negotiator commented: “Perhaps I shouldn’t say this, but some heads of state had trouble understanding the implications of the 2 °C target; sometimes they even accidentally talked of limiting global warming to 2%. I’m glad that we now have those 1024 Joules which are much easier to grasp for policy makers and the public.”

This fictitious newspaper item is of course absurd and will never become reality, because ocean heat content is unsuited as a climate policy target. Here are three main reasons why.

1. Ocean heat content is extremely unresponsive to policy.

While the increase in global temperature could indeed be stopped within decades by reducing emissions, ocean heat content will continue to increase for at least a thousand years after we have reached zero emissions. Ocean heat content is one of the most inert components of the climate system, second only to the huge ice sheets on Greenland and Antarctica (hopefully at least – if the latter are not more unstable than we think).

AR5 Fig 3.2

Figure 1. Ocean heat content in the surface layer (top panel, various data sets) and the mid-depth (700-2000 m) and deep ocean (bottom panel), from the IPCC AR5 (Fig. 3.2 – see caption there for details). Note that uncertainties are larger than for global mean temperature, the data don’t go as far back (1850 for global mean temperature) and data from the deep ocean are particularly sparse, so that only a trend line is shown.

2. Ocean heat content has no direct relation to any impacts.

Ocean heat content has increased by about 2.5 X 1023 Joules since 1970 (IPCC AR5). What would be the impact of that? The answer is: it depends. If this heat were evenly distributed over the entire global ocean, water temperatures would have warmed on average by less than 0.05 °C (global ocean mass 1.4 × 1021 kg, heat capacity 4 J/gK). This tiny warming would have essentially zero impact. The only reason why ocean heat uptake does have an impact is the fact that it is highly concentrated at the surface, where the warming is therefore noticeable (see Fig. 1). Thus in terms of impacts the problem is surface warming – which is described much better by actually measuring surface temperatures rather than total ocean heat content. Surface warming has no simple relation to total heat uptake because that link is affected by ocean circulation and mixing changes. (By the way, neither has sea-level rise due to thermal expansion, because the thermal expansion coefficient is several times larger for warm surface waters than for the cold deep waters – again it is warming in the surface layers that counts, while the total ocean heat content tells us little about the amount of sea-level rise.)

AR5 Fig 3.1
Figure 2. Temperature anomaly in °C as a function of ocean depth and time since 1955. (Source: Fig. 3.1 of the IPCC  AR5.)

3. Ocean heat content is difficult to measure.

The reason is that you have to measure tiny temperature changes over a huge volume, rather than much larger changes just over a surface. Ocean heat content estimates have gone through a number of revisions, instrument calibration issues etc. If we were systematically off by just 0.05 °C throughout the oceans due to some instrument drift, the error would larger than the entire ocean heat uptake since 1970. If the surface measurements were off by 0.05 °C, this would be a negligible correction compared to the 0.7 °C surface warming observed since 1950.

Two basic ocean physics facts

Let us compare the ocean to a pot of water on the stove in order to understand (i) that heat content is an integral quantity and (ii) the response time of the ocean.

Imagine you’ve recently turned on the stove. The heat content of the water in the pot will increase over time with a constant setting of the stove (note that zero emissions correspond to a constant setting – emitting more greenhouse gases turns up the heat). How much heat is in the water thus depends mainly on the past history (how long the stove has been on) rather than its current setting (i.e. on whether you’ve recently turned the element up a bit). That is why it is an integral quantity – it integrates the heating rate over time. You can tell from the units: heat content is measured in Joules, heating rate in Watts which is Joules per second, i.e. per unit of time.

The water in the pot heats up much faster than the global ocean. The water in the pot may be typically ~10 cm deep and heated at a rate of 1500 Watt or so from below. But the ocean is on average 3700 meters deep (thus has a huge heat capacity) and is heated at a low power input of the order of ~1 Watt per square meter of surface area. Also it is heated from above and not well mixed but highly stratified. Warm water floats on top, which hinders the penetration of heat into the ocean. Water in parts of the deep ocean has been there for more than a millennium since last exposed to the surface. Therefore it will take the ocean thousands of years to fully catch up with the surface warming we have already caused. That is why limiting ocean heat content to 1024 Joules is not possible even if we stop global warming right now – even though this amount is four times the amount of heating already caused since 1970. Ocean heat content simply does not respond on policy-relevant time scales.

If you turn your setting on the stove higher or lower, what you immediately change is the rate of heating – the wattage. So would limiting the rate of ocean heat uptake be a suitable policy target? At least it would be responsive to policy at a relevant time scale, like surface temperature. But here reasons two and three come into play. The rate of heat uptake has even less connection to any impacts than the heat content itself. And the time series of this rate is extremely noisy.

ocean_bottom

Charles Saxon in the New Yorker on the impacts of deep ocean heat content on society.

So why do Victor and Kennel propose to use deep ocean heat content as policy target?

In a recent interview, David Victor has explained why he wants to “ditch the 2 °C warming goal”, as the title of his Nature commentary with Charles Kennel reads:

There are some other indicators that look much more promising. One of them is ocean heat content.

The reason that Victor and Kennel gave for preferring ocean heat content over a global mean surface temperature target is this:

Because energy stored in the deep oceans will be released over decades or centuries, ocean heat content is a good proxy for the long-term risk to future generations and planetary-scale ecology.

I criticized this because the deep ocean will not release any heat in the next thousand years but rather continue to absorb heat. In his response at Dot Earth, Victor replied that I had “plucked this sentence out of context”. However, in their article there simply is no context that would explain how “energy stored in the deep oceans will be released over decades or centuries” or how this would make it “a good proxy for the long-term risk”. This statement is plainly wrong, and Victor would have been more credible to simply admit that. Victor there further argues that “the data suggest [OHC] is a more responsive measure” than surface temperature, but what he means by that, given the huge thermal inertia of the oceans, beats me.

My impression is this. Victor and Kennel appear to have been taken in by the rather overblown debate on the so-called ‘hiatus’,  not realizing that this is just about minor short-term variability in surface temperature and has no bearing on the 2 °C limit whatsoever. In this context they may have read the argument that ocean heat content continues to increase despite the ‘hiatus’ – which is a valid argument to show that there still is a radiative disequilibrium and the planet is still soaking up heat. But it does not make ocean heat content a good policy target. The lack of response to short-term wiggles like the so-called ‘hiatus’ points at the fact that ocean heat content is very inert, which is also what makes it unresponsive to climate policy and hence a bad policy target. So my impression is that they have not thought this through.

I agree with the criteria that a metric for a policy goal needs to be (a) related to impacts we care about (otherwise why would you want to limit it) and (b) something that can be influenced by policy. A more technical third requirement is that it must be something we can measure well enough, with well-established data sets going far enough back in time to understand baseline variability.

But it seems clear to me that global mean surface temperature is the one metric that best meets these requirements. It is the one climate variable most clearly linked to radiative forcing, through the planetary energy budget equation. The nearly linear relation of cumulative emissions and global temperature allows one to read the remaining CO2 emissions budget off a graph (Fig. SPM.10 of the AR5 Summary for Policy Makers) once the global temperature target is agreed. Most impacts scale with global temperature, and how a whole variety of climate risks – from declining harvests to the risk of crossing the threshold for irreversible Greenland ice sheet loss – depends on temperature has been thoroughy investigated over the past decades. And finally we have four data sets of global temperature in close agreement (up to ~0.1 °C), natural variability on the relevant time scales is small (also ~0.1 °C) compared to the 2 °C limit, and models reproduce the global temperature evolution over the past 150 years quite well when driven by the known forcings.

I find the arguments made by Victor and Kennel highly self-contradictory. They find global mean temperature too variable to use as a policy target (that is the thrust of their “hiatus” argument) – but they propose much more noisy indicators like an index of extreme events. They think global surface temperature is affected by “all kinds of factors” – and propose ocean heat content, which is determined by the history of surface temperature. Or the surface area in which conditions stray by three standard deviations from the local and seasonal mean temperature, which is a straight function of global surface temperature with some noise added. They argue surface temperature is something which can’t directly be influenced by policy – and propose deep ocean heat content where this is a hundred times worse. They say limiting warming to 2 °C is “effectively unachievable” – and then say “it’s not going to be enough to stop warming at 2 degrees“. I simply cannot see a logically coherent argument in all this.

martin-argo

My long-time friend and colleague Martin Visbeck launching an Argo float in the Pacific.

The bottom line

Should we monitor heat storage in the global ocean? By all means, yes! The observational oceanography community has long been making heroic efforts in this difficult area, not least by getting the Argo system off the ground (or rather into the water). That is no small achievement, which has revolutionized observational physical oceanography for the upper 2,000 meters of the world ocean. Currently Deep Argo is under development to cover depths up to 6,000 meters (see e.g. News&Views piece by Johnson and Lyman just published in Nature). These efforts need and deserve secure long-term funding.

Is ocean heat storage a good target for climate policy, to replace the 2 °C limit? Certainly not! I’ve outlined the reasons above.

 

[p.s. I am grateful that David Victor has apologized to me for comparing it to “methods of the far right” that I introduced him as a “political scientist” in my previous post (as in fact he is in the intro to his interview). This matter is now settled and forgotten, with no hard feelings.]

 

Update 21 October: I thank David Victor and Charles Kennel for responding to this article below. Answering this again would turn the discussion in circles – I’ve made my points and I think our readers now have a good basis to form their own opinion. Just one piece of additional data that might be informative, since Victor and Kennel below suggest to use the rate of heat content change for a well-measured portion of the ocean, rather than absolute heat content. Below I plotted the annual heat uptake of the upper 700 meters. (I already made this plot last week, it is the basis of me saying above that this measure is very noisy – the data can be downloaded from NOAA.)

ocean heat uptake

155 Responses to “Ocean heat storage: a particularly lousy policy target + Update”

  1. 1
    Edward Greisch says:

    Politicians can misinterpret anything they want to.

  2. 2
    Halstead Harrison says:

    Limiting ocean heat content to 10^24 Joules will open serious problems of measurement, even within factors of 10. Perhaps that’s the idea? “Let’s argue about measurements, not consequences.”?

  3. 3
    Bob Finch says:

    I find this entire discussion disturbing. Academics who obviously care about bending the emissions curve and minimizing long term impacts of climate change are arguing about semantic minutiae. I understand 450 ppm CO2 and 2 degrees Celsius and a trillion tons of carbon. If I can’t rely on these benchmarks, how can I intelligently discuss the issues with my local policy makers? Why should I even bother?

    What I don’t see are serious efforts to stabilize and reduce emissions either at the local or national level in the United States or China and I see efforts to weaken reduction programs in Canada, Australia, and India. Global emissions increased in 2013 according to the Global Carbon Project. The fossil industry is doubling down on coal, oil and gas production and flooding the airways with messages touting clean and safe energy providing jobs for millions.

    I think the only hope for a stable climate is climate sensitivity to increased levels of greenhouse gases at the extreme low end of the scale.

  4. 4
    Shelama says:

    Pielke Sr. early on and years ago vigorously advocated OHC as the best metric to measure global warming.

    I miss Pielke’s blog and don’t believe I’ve heard anything from or about him for years. Is he still alive? (The last I heard he was helping Watts get his “game changing paper” ready for prime time.

  5. 5

    Dr. Rahmstorf

    You have presented several reasons not to use ocean heat content changes as the metric to diagnose global warming and to present this information to policymakers. Unfortunately, you have not properly framed your reasoning.

    First, all physicists would agree that heat is measured in Joules. Thus an increase in Joules is heating. In the context of global warming, it must involve an accumulation of Joules. The ocean is the largest component of the climate system in terms of its heating and cooling. I assume you agree with this.

    A global average surface temperature trend (i.e. the 2C) threshold is only a two dimensional sample of the actual three dimensional mass field in which heat changes on multi-decadal time periods occurs.

    As I wrote in my paper

    Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335

    “…the surface temperature is a two-dimensional global field, while heat content involves volume integrals..”

    See also

    Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55. http://pielkeclimatesci.files.wordpress.com/2009/10/r-334.pdf

    The models, of course, must be able to show skill at predicting the climate system heat changes

    As written in

    Barnett, T.P., D.W. Pierce, and R. Schnur, 2001: Detection of anthropogenic climate change in the world’s oceans. Science, 292, 270-274

    “..a climate model that reproduces the observed change in global air temperature over the last 50 years, but fails to quantitatively reproduce the observed changed in ocean heat content, cannot be correct.”

    As Jim Hansen wrote in a communication to John Christy and I [http://pielkeclimatesci.files.wordpress.com/2009/09/1116592hansen.pdf]

    “our simulated ocean heat storage (Hansen et al., 2005) agrees closely with the observational analysis of Willis et al. (2004). The decadal mean planetary energy imbalance, 0.75 W/m2 , includes heat storage in the deeper ocean and energy used to melt ice and warm the air and land. 0.85 W/m2 is the imbalance at the end of the decade [Jim is referring to the 1990s].”

    My questions to you are:

    1. Do you agree that the ocean is the dominate reservoir of heat changes on multi-decadal time scales?

    2. Do you agree that if the spatial and temporal sampling is adequate, changes in the ocean heat content can be used to diagnose the radiative imbalance of the global climate system (i.e. global warming)?

    3. What is your best estimate of the current [2014] global radiative imbalance, and how do you obtain this value?

    4. What is the current [2014] radiative forcing from added CO2?

    5. What do the latest multi-decadal global climate models predict is the current radiative imbalance, given than Jim Hansen said it was 0.85 W/m2 at the end of the 1990s, based on his comparison with ocean heat change data?

    6. As a metric to diagnose and predict changes in regional and local climate impacts that matter to society and the environment, is the global average surface temperature trend, or are multi-decadal changes in major atmospheric and ocean circulation features, more important?

    I look forward to your answers.

    [Response: 1 – Yes. 2 – The radiative imbalance is a measure of the disequilibrium caused by the fact that (mainly) the ocean has not yet caught up with the recent increase in forcing. It thus is a measure of the further global warming that we are committed to even if we do not increase the forcing any further but keep it constant. It is not a measure of the global warming that is already observed. 3, 4, 5 – it is not part of my own research to make such estimates, so I don’t have my own best estimate. I’d simply look up the current numbers in the IPCC report and more recent scientific literature – but you can do that yourself. 6 – Regional changes can indeed be affected by changes in oceanic or atmospheric circulation. Predicting those is very hard though, and thus far the observed first-order picture is that you can understand the pattern of global warming (if you look at a map of temperature trends over the past hundred years or so, as shown in the IPCC reports) to a first approximation as an increase in the global mean modified by thermal inertia, i.e. greater warming over continents than the oceans, and ice/snow albedo amplification in high-latitude areas. There are some regional exceptions (e.g. cooling in the North Atlantic subpolar gyre) that may be related to circulation changes. – Stefan]

  6. 6
    Maria says:

    Is it really the case that “Ocean heat content is one of the most inert components of the climate system”? Who warms the world during night and winter time?

    [Response: It is exactly that thermal inertia which keeps marine areas warmer in winter and cooler in summer compared to the continents, because they don’t respond so strongly to the seasonal cycle. -Stefan]

  7. 7
    Kenji Katsuragi says:

    We have to act.

  8. 8
    Roger Tattersall says:

    “the ocean is on average 3700 meters deep (thus has a huge heat capacity) and is heated at a low power input of the order of ~1 Watt per square meter of surface area.”

    The oceans are heated at a rate of up to around 1kw at zenith by the Sun, and have to lose that energy at the same rate as it is input in order to be somewhere near equilibrium. In order to overcome the restrictions placed on the ocean’s energy emission by sea level pressure and the insulative effect of the overlying air, the ocean’s surface has to rise to a temperature at which it can evaporate and radiate the same amount of energy as enters it.

    Longwave back-radiation does not heat the ocean directly, but raises the temperature of the near surface air, reducing the temperature differential between the air and the ocean’s surface. Given that oceanic energy emission supports the night-time temperature of the near surface air, and daytime evaporation produces dominant energy transport to altitude it is evident that the level of back-radiation in the air is more an effect of ocean surface temperature (and heat content) than a cause of it.

    [Response: I was talking about the net heating rate, since the article is about changes in global ocean heat content. -Stefan]

  9. 9
    Paul Williams says:

    I agree with the target.

    The Oceans absorbing 1.0 x 10^24 joules of energy would equivalent to the ocean down to 2000 metres increasing in temperature on average by about 0.5C (versus only 0.09C to date). At that level (or at a rate that reaches that level in 100 years), we could definitely say we are dangerously warming the Earth with GHGs and there should be efforts to avoid it.

  10. 10
    James Picone says:

    Maria@6: Ocean surface temperatures (and, therefore, surface heat content) track seasonal variations and day/night, but total ocean heat content is much, much larger than the heat content of the surface layer that varies with those factors.

    You might also want to consider what happens when you have a pot of boiling water on the stove and turn the heat off – it takes a while for it to cool down to room temperature. Works just as well when instead of a pot of water on the stove you have a hemisphere of air in space near a star. Also there’s convection and conduction from the bits of Earth that are in sunlight. And there’s still sunlight in winter, just less of it.

    Alternately, try thinking about a spit roast – what heats up the bit of the roast that’s directly opposite the fire?

  11. 11
    Konrad says:

    Before policy should come solid science. In terms of climate on our ocean planet, OHC remains a critical metric. Effecting OHC are such factors as cloud cover, mineral and biological turbidity, wind speeds and component variation in TSI. However one factor that is provably negligible in OHC is DWLWIR.

    Currently climate modelling has critical flaws when it comes to modelling solar heating of the oceans. The most basic 2D modelling treats the oceans as SW opaque, and this leads to grave errors, in particular the basic 255K assumption for “surface without atmosphere”. Some more advanced modelling does try to address the depth of solar absorption issues. Sweeny et al is a fair example –
    http://www.ldeo.columbia.edu/~csweeney/papers/SWpen_Sweeney.pdf

    Simple empirical experiments can show that DWLWIR is a negligible factor in OHC and depth of UV/SW absorption by contrast a critical factor. But to address modelling issues more precise empirical environmental measurement is needed. Dr. Rahmstorf mentions the development of Deep Argo which will be a great resource. It could be a fantastic resource with the addition of two extra instruments –
    1. Optical turbidity sensor.
    2. Multi wavelength solar penetration sensor.

    There have already been some disturbing moves to use just atmospheric CO2 concentration as a metric driving policy without regard to actual measurable climate effects. Abandoning OHC as a climate metric would be allowing politics to drive science, when science should be driving policy.

    [Response: All current coupled climate models include wavelength-dependent penetration of SW into the ocean and some even include the impacts of varying Chlorophyll on that penetration. Rather than being a fundamental flaw, it is in fact a very minor difference. – gavin]

  12. 12
    Nick says:

    Puzzled by the comment by Dr Pielke Sr. I find the framing of the reasoning very easy to follow. Dr Rahmstorf is emphasising policy target use of a metric, not a warming diagnostic use.

  13. 13
    Geoff Russell says:

    I’m confused. I understand how global (air) temperatures can rise for decades after we have stopped emitting carbon (well I think I do!), but how on earth can ocean heat content rise significantly? Assume we stop putting carbon up in the sky and that therefore the radiative balance is zero. I.e., the energy arriving matches that leaving. Then for ocean heat content to rise, it must be coming from somewhere. So where can it come from? I can imagine all kinds of redistributions, but not a rise in total ocean heat content.

    [Response: If we stop adding CO2, the radiative imbalance will not be gone. It will only gradually disappear as the ocean catches up with the warming and stops absorbing heat. As less and less heat disappears into the ocean, the surface will have to balance a greater part of the radiative forcing and get warmer. That is why ocean heat uptake (i.e. thermal inertia) keeps the surface cooler, until finally the system approaches a new equilibrium. Hope this is clear? -stefan]

  14. 14
    David Victor and Charlie Kennel says:

    We welcome the opportunity to debate the question of goal-setting for climate policy. Thanks to Stefan for his posts on this, and here we respond to the issues he raises that we haven’t examined in other posts. Over the last two weeks our piece in Nature has triggered debates on Andy Revkin’s dot Earth blog and on the Yale 360 site. We urge folks to look at what we’ve posted there as well.

    Our piece in Nature addressed two main issues. One was the question of how to set the right metrics for climate goals—should it be long-term average global temperature (e.g., 2 degrees) or something else. The other was whether the existing metric (2 degrees of temperature, or any other partial equivalent such as target for greenhouse gas concentrations that is broadly equivalent to 2 degrees) is achievable. Stefan’s post concerning OHC is about the first of these two issues, so we’ll focus there.

    Our article did NOT suggest that we translate climate goals into a single, long term indicator such as OHC. What we said was that there should be a basket of indicators. A basket would condition the public and policy makers to look at a wide range of vital signs—causes of human stress on the climate system as well as symptoms—rather than any single indicator that may be unresponsive to policy and might be torqued by natural variability over many years. (That conditioning is a political process more than a scientific one, but the politics here are an important part of the equation.) We suggested that OHC be in that basket because so much of the excess heat goes into the oceans. We have looked at total column OHC (0-2000 meters). With effort, scientists might decide that a subset of the OHC measures (e.g., just portions of the shallower measurements and perhaps OHC adjusted for sampling coverage in various ways) might be better. But we don’t think OHC alone would do the job. What we do think is that policy makers would be better off selecting indicators in the basket that are sensitive to the human stresses on the climate system so that there is, to the extent possible, a relationship over the long term between what policy makers actually do (adopt policies to control emissions and manage exposure to extreme events) and observable outcomes.

    Stefan takes us to task because OHC isn’t responsive to policy. We agree that OHC is a long-term indicator and cannot respond to short-term policy goals, but to us that is its virtue. It measures committed risk to future generations. (Similar problems of unresponsiveness to policy befalls global average surface temperature—perhaps more so. As folks know, we think OHC may be—along with a basket of other indicators—better than average surface temperature in providing that function. But let’s debate that fully.) The lack of a direct relationship to policy is why no serious goal-setting enterprise would focus only on long-term goals—indeed, that is one reason we wrote our article. A useful basket would also include nearer term goals and indicators as well. That’s why the comparison we made with the millennium development goals (MDGs) is important—and our original draft of the Nature essay (reprinted on Revkin’s dot Earth site) talked about other goal-setting examples as well. The MDGs were explicitly NOT set in terms of long-term aspirations such as ending all poverty or ending under-development. Instead, they were set as nearer term goals such as halving extreme poverty. And those near-term goals were turned into specific indicators that real organizations could measure and use to assess performance.

    We suspect we all may be talking past each other, a bit, on the matter of OHC. We have sensed in this debate that lots of folks are redoubling the defenses around long-term average temperature such that we can’t really have an honest debate about alternatives. For example, in Stefan’s caricature New York Times story that opens his post he points to the 10^24 joule goal. If we had a serious debate about using OHC as part of a basket of goals then most likely we would decide not to measure progress in absolute order of magnitudes but in rates of change—perhaps (as suggested above) for a subset of the oceans rather than the full column (for all the reasons about the sheer size of the deep oceans that Stefan flags in his post). And we’d do that not just with OHC but other goals or indicators that are sensitive to human perturbation, such as higher latitude temperatures. Each of those elements—including perhaps global average temperature—would be rolled up into the long-term goals. But for policy makers much more important would be to set nearer term goals that are more closely connected to what policy makers actually do—such as emissions of gases and policies to control those emissions, or perhaps concentrations of gases. We are enamored with the idea of measuring TOA radiative imbalances as the best, full measure of human stress on the climate system—that’s something that Jim Hansen and others have also flagged as important—but we gather it can’t be done reliably right now. That’s another reason to have a serious debate over goal setting—so that we create incentives to develop the techniques needed to do better monitoring. (There are lots of examples in monetary and industrial policy where better indicators have emerged in direct response to well-articulated policy needs. We should learn those lessons and apply them here. )

    Over the last two weeks various people have said that baskets of goals will be more complex than single goals and that will make them abhorrent to policy makers. We say: complexity is intrinsic to the issue here, and policy makers are actually quite used to dealing with complex goals. Think of modern banking regulation or international policy coordination. Or think of development policy and the MDGs. They are fantastically complex. Yet real policy makers digest that information because they know they need to. As we pointed out, real doctors go beyond temperature to a range of other vital signs.

    Finally, we also agree that the hiatus is likely to correct itself over time. In another hundred years, it will be seen in proper context. Our issue is that the hiatus is frequently cited today as an excuse for inaction. Since it started, 16 valuable years have passed, GHG concentrations have increased, and climate risks have accumulated; we can only speculate on how many positive initiatives have been repressed by the diminished sense of urgency, particularly in the many communities and regions asking whether and when they should prepare to adapt. We fear that many of the people responsible for making and/or supporting such decisions do not have a sense, as climate scientists do, of how complex nonlinear systems behave, have no feeling how the climate behaved in the past, and do not have the benefit of 40 years’ modeling experience. All of these condition us scientists to be comfortable with natural internal variations. But it is a difficult case to make to those without our background, as the popular “natural cycle vs. human-caused” debate makes clear. Had policy and communications conditioned the public to looking at a basket of indicators as well as temperature it would have seen that the case for urgent action based upon observed climate change has grown stronger. But let us emphasize that this was a point that relates to important political and communication issues and an argument we made in passing in the article—it is NOT the central reason to move beyond temperature. The central reason is to have the indicators line up with the full range of human stresses and responses by the climate system while also to set goals in terms that are actually achievable.

    Sincerely

    David and Charlie.

    PS; Finally, let me, David, just respond on the matter of the apology. The question here was whether I had inappropriately reacted to Stefan’s characterization of our academic fields. My goal wasn’t to cause offense but to explain how the way that we were introduced subtly sent signals to readers about the credibility of our message. In my response to Stefan I noted that my comments (on the dot Earth site) were mainly focused on how Joe Romm had used our professional qualifications (i.e., we aren’t climatologists) to signal that our work should be disparaged. I wasn’t the only person who noticed that—so did Andy Revkin and he said as much in his introduction to the debate. If Andy notices something like that—he is a professional communicator after all—then that is a worry to me. Stefan wrote me and was annoyed and said it was his custom to introduce people according to their discipline, and he suggested that his introduction of us was quite in line with what he does normally. So I checked—and read 5 years of Stefan’s blog posts on RealClimate only to find that not in a single case was any introduction to a scientific debate prefaced by information about the disciplinary qualifications of the authors. The only time it was done was in his preface to our piece. I don’t think this is a big deal, and I don’t want to cause any further offense, but my point was just that serious goal-setting is an interdisciplinary and highly political activity and it requires people from different disciplines. And if folks in one disincline use subtle language to suggest that folks in another aren’t qualified then that makes it hard to have a serious debate about intrinsically interdisciplinary issues. So I was not trying to cause offense but just trying to make that point. And I have done that again when I wrote back to Stefan in his original protest to me. In my next post on this site I will put up the whole email exchange so that everyone can see what was written since some of that content may be useful.

  15. 15
    David Victor says:

    COPY OF EMAIL TRAFFIC RELATED TO DISCIPLINARY INTRODUCTIONS….

    Folks, as promised in the post that Charlie and I just put on this website, in the PS i promised to share a copy of the email traffic relating to the question of offense and apology. here it is…

    Dear Stefan

    thanks for your note. I apologize if I have offended you. My comments about the tone were directly centrally at Joe Romm’s post—which artfully took the introduction to your post and then spun it out into a larger veiled critique of our qualifications. I was hardly the only person to pick up on this—indeed, Andy Revkin, a seasoned observer of the scene, made a special point of mentioning the same thing (focused on Joe’s post). So that was the central point of my opening comments.

    I can appreciate that you work with people from lots of different backgrounds and it is important to know and understand those different backgrounds. (Small world that it is, I visited PIK several times right when John founded the place—and I remember, from the outset, the goal was to have people working together from different disciplines. I’ve done the same in my career.) Language can be a funny and subtle thing, and thus to look further into your email I had the good opportunity to read every one of your RealClimate posts for the last five years. You may be unaware of it, but as far as I can tell the only blog post you introduced on a technical topic with information about the authors’ disciplinary backgrounds was the one that you posted about us. Just one in 5 years. (The only other post by you over that entire history that mentions prominently the author’s disciplinary background was a post about Ian M, the novelist; and that post was about a novel.) So I just caution—which was the larger point of the opening paragraph of my remarks—that we are often signaling to people what we think about the credibility of their work by the modifying language we use.

    Regarding substance, my view is that there are two issues with the 2 degree goal. One is the question of whether, geophysically, that is the right way to measure human stress. Ultimately I think Jim Hansen is right and we should focus on TOA imbalance—when that can be measured reliably. Absent a single clean indicator, a basket would be better. I appreciate your blog post from Sept 25 2013 that points to OHC. We also think OHC has promise, along with other measures. But that’s an area of ongoing debate. The other question is the stringency of the goal, which for now I’ll talk about in temperature terms even though the policy community needs to focus on other/additional measures. If we care about climate impacts on nature then 2 degrees is too much. If we care about impacts on well-managed human infrastructure then 3 degrees might be fine. I see the goals as like a menu in a restaurant. The meal that gets ordered is a combination of the items on the menu and what people are willing to buy. I love caviar and truffles but I am unwilling to pay for them. As a policy analyst, my concern is that we have put one item on the menu (2 degrees) and governments have pretended to order it, but in fact no meal is being served.

    2 degrees is unachievable (absent some tremendous luck on climate sensitivity) but protecting nature requires less than 2 degrees. the solution is to set goals that are achievable—but which require the maximum stretch of effort. I don’t know what those goals are because they require ordering decisions by governments from a menu. Maybe the equivalent of 2.5 degrees is feasible—or perhaps it is just 3. I am not say that is what we WANT—it is what we can get. And even that will require massive efforts.

    Here the comparison with the MDGs is instructive. We might want to end poverty. But the MDG was to halve extreme poverty. We might want to reverse and shrink HIV/AIDS, but the MDG was to halt the spread. Some of the actual goals align with what we might want in an ideal world—such as universal primary education. Setting goals that are within the realm of the achievable and which can be measured over time horizons that are relevant to governments and other key players can inspire a lot of action. For example, see the regular World Bank/IMF implementation report on the MDGs:
    http://www.worldbank.org/en/news/press-release/2014/10/08/wb-imf-report-progress-development-goals-promoting-shared-prosperity

    This is the kind of serious, goal-oriented work that we need in climate.

    best

    david

    From: Stefan Rahmstorf
    Date: Friday, October 10, 2014 at 7:42 AM
    To: “David G. Victor”
    Subject: the 2 C debate

    Dear David,

    I enjoy having a good debate on the 2 °C limit. From your response to my RealClimate article, I gather you misunderstood the fact that I introduced you and your coauthor by the fields of your published research (as I looked them up on Web of Science) as meaning to imply that you are not qualified to comment on the 2 °C limit. That of course was neither said nor was it my intention at all – as a working scientist, and for a science blog, I think it is entirely normal to introduce people by the research area they have worked in, and to ignore titles, administrative positions held etc. (It wouldn’t occur to me to be offended if someone introduces me as physical oceanographer or climatologist without mentioning my titles, government advisory role etc.) In fact I would argue that you as a political scientist (which you are, right? or did I get this wrong?) are much more qualified to judge what is useful as a target in a political context than I am as a natural scientist, so I was rather surprised by the interpretation you attached to this. (On the other hand, I do feel more qualified on matters of oceanography.) I’ve been working for two decades in a highly interdisciplinary institute in Potsdam, together with political scientists, economists and other social scientists, as well as working for 8 years in the German Advisory Council for Global Change, equally interdisciplinary – with many excellent colleagues and friends that I have great respect for. So it simply did not occur to me that anything offensive could be in the term political scientist.

    In any case, merely naming your research fields can hardly be construed as a personal attack or something that would be inappropriate in a collegial discourse. However, saying that I use “the same tactics that are often decried of the far right” is to me clearly outside a normal collegial discussion. But I’d be happy to let this rest and forget about it if I receive an apology for this inappropriate comparison.

    Finally I would be grateful if I could get some clarification from you on what you mean. Am I right that the main thrust of your argument is to use new targets that would imply less rapid emissions reductions, i.e. a larger cumulative emissions budget? I conclude this from your argument that 2 °C is unachievable. On the other hand, in your recent interview with Diane Toomey you say “It’s not going to be enough to stop warming at 2 degrees.” That sounds as if we should do more than that. What more did you mean? Apparently not more rapid emissions cuts?

    Regards, Stefan


    Stefan Rahmstorf
    Head of Earth System Analysis, PIK
    Researcher-ID: A-8465-2010
    Public PGP Key

    [Response: Actually would have been nice to be asked before you publish an email addressed to you personally on the internet. -stefan]

  16. 16
    Chris Colose says:

    Roger in #5 says:

    “A global average surface temperature trend (i.e. the 2C) threshold is only a two dimensional sample of the actual three dimensional mass field in which heat changes on multi-decadal time periods occurs.”

    First of all, the metric that should be of interest to policymakers is carbon emissions (See e.g., my comment here). Ultimately, whatever your favorite diagnostic of climate is- OHC, surface T, etc, it will be slaved to changes in future CO2 concentrations, which in turn will be dominated by anthropogenic sources. It’s also the future emissions that determines ocean acidification.

    Putting all this aside, Roger’s objection makes no sense. The surface is the 2-D(ish) plane in which humans live on, and therefore it’s of interest. But actually the whole troposphere is pretty much yoked together convectively and so you remove a degree of freedom when thinking about the vertical T profile- if you want the temperature 10 km up you can do a pretty good job predicting it from the surface T change, not so much how many more joules you got. This, in turn, determines things like future moisture content and changes in extremes. Because of how good many metrics (e.g., Arctic sea ice) scale with global temperature, it’s value as a metric of climate change simply will not go away, so it’s not worth advocating against it. Obviously the “heat” is important but that alone doesn’t complete the story.

    The statements about climate models needing to get OHC changes correct in order to be correct is trivially true (by definition) but irrelevant here.

  17. 17
    Thomas says:

    The one the OHC has going for it is being roughly the third integarl in time of emissions (emissions intagrate to concentration, integrates to surface temperature, integrates to OHC), and so -under the assumption we could acurately measure it has low noise. The problem is, as you have mentioned that it will continue to rise for several hundred years, even if we do the right thing.
    What about near surface OHC (say the top 250meters)? This has the advantage that its time costant is much lower, and is also more relevant to impacts. It would largely share in the purported benifits of overall OHC (reduced time series noise), but I think would be more closely related to impacts.

  18. 18

    To my perception, using average ocean pH levels as an energy policy metric would avoid your three objections while being less ambiguous than the progress of climate change with regard to the negative impacts on biological diversity and thus on prospective human survival: http://www.theeuropean.de/jeffrey-michel/8788-meeresschutz-entscheidend-fuer-das-weltklima

  19. 19
    Geoff Russell says:

    Thanks stefan for the explanation, it is indeed clearer.

  20. 20
    JCL says:

    I was first referred to a piece by David G. Victor by a person who held typical «denier» beliefs: that global warming was not happening and a conspiracy by scientists, etc. This piece is, from what I understand, the text of a conference he gave, entitled «Why do smart people disagree about facts?»

    In this, Victor presents, among others, the following ideas:

    – That funding of climate denial by the fossil fuel industry has been exaggerated;
    – That the funding of scientists who deny global warming no longer comes from the fossil fuel industry, but from anonymous donors, therefore they have become credible;
    – That the amount of funds anti-climate change organizations have at their disposal is insignificant;
    – That the term «denialist» should not be used, as it is derogatory – YET MR VICTOR USES THE TERM «CLIMATE BELIEVER» throughout this same essay;
    – That climate change denial can no longer be dismissed since Freeman Dyson (of GWPF fame) expressed his doubts on global warming.

    Of course, we know very well who is behind the anonymous money and that the amounts are far from insignificant:

    http://www.scientificamerican.com/article/dark-money-funds-climate-change-denial-effort/

    So why did David Victor come out trying to start a debate about insignificant details in the run up to the Paris conference?

    I have very little doubt.

  21. 21
    Rod B says:

    I found this informative and enlightening.

  22. 22
    mitch says:

    In a perverse way I agree that we need more than one metric. (1) Historic and continuing CO2 emissions is a great metric and probably the most important, since it helps to track where the inadvertent geoengineering is coming from and how much effect we will have. (2)Surface temperature is actually a very useful metric since it is a quick measure of change in the surface system where weather is generated. People also know what we mean by temperature even though ‘global’ confuses many (3) Ocean heat content is actually most useful to better understand transient climate sensitivity, but the best measure is OHC above and below the thermocline, since that shows how easily energy is being passed to the deep ocean to be stored.

  23. 23
    Hank Roberts says:

    Why is ocean pH not being used as the bright line indicator?

    If we don’t reverse that change in the oceans, far worse damage is done than we do by warming the air.

  24. 24
    Hank Roberts says:

    Oh, and on why ocean pH seems a critical indicator of how we’re managing, or not:

    When we talk about global carbon fixation –”pumping” carbon out of the atmosphere and fixing it into organic molecules by photosynthesis – proper measurement is key to understanding this process. By some estimates, almost half of the world’s organic carbon is fixed by marine organisms called phytoplankton – single-celled photosynthetic organisms that account for less than one percent of the total photosynthetic biomass on Earth….
    … The scientists estimated that an algal patch of around 1,000 sq km – which forms within a week or two – can fix around 24,000 tons of organic carbon – equivalent to a similar area of rain forest. Since a viral infection can rapidly wipe out an entire bloom, the ability to observe and measure this process from space may greatly contribute to understanding and quantifying the turnover of carbon cycle and its sensitivity to environmental stress conditions, including marine viruses.

    http://wis-wander.weizmann.ac.il/the-ocean’s-living-carbon-pumps

    Maybe the inconvenience to us of warming the atmosphere isn’t critical compared to the problem we’re causing for the other organisms living on the planet.

    Shouldn’t we use the well-being of the one percent — the phytoplankton — as our critical indicator?

  25. 25

    Dr. Rahmstorf

    With respect to your reply on #2 you write

    “The radiative imbalance is a measure of the disequilibrium caused by the fact that (mainly) the ocean has not yet caught up with the recent increase in forcing. It thus is a measure of the further global warming that we are committed to even if we do not increase the forcing any further but keep it constant. It is not a measure of the global warming that is already observed.”

    This is an incorrect description of the physics.

    The change in Joules in the ocean can be directly used to diagnose the global average radiative imbalance at the top of the atmosphere over the time period of the change. There is no further warming if the oceans stopped increasing in Joules [neglecting any smaller part associated with ice melting, soil etc].

    If the TOA radiative imbalance would remain constant and positive, an increase in Joules would result. The two are interchangeable. While there is a lag in the global average surface temperature response, no such lag is involved in this relationship between global average radiative imbalance and ocean heat changes. This is a major advantage of using ocean heat content changes as the primary metric to diagnose global warming and to communicate this aspect of climate to policy makers,

    I recommend you, and your readers, look at the paper

    Ellis et al. 1978: The annual variation in the global heat balance of the Earth. J. Geophys. Res., 83, 1958-1962. http://pielkeclimatesci.files.wordpress.com/2010/12/ellis-et-al-jgr-1978.pdf

    particularly their Figure 4.

    Their abstract reads

    “An annual variation with a range of 31 W m -• is found in the global net radiation balance of the earth.
    The net radiation flux values measured from satellites and the changes in total heat content computed
    from independent sets of atmospheric and oceanic data show annual variations which are consistent with
    each other in both phase and magnitude. The net energy gain and loss by the planet within a year is
    stored and released within the system primarily by the oceans.”

    While I do not know if the values they present remain robust, but their approach is.

    Roger

  26. 26

    Dr. Rahmstorf

    On your replies to # 3, 4, 5 you wrote

    “- it is not part of my own research to make such estimates, so I don’t have my own best estimate. I’d simply look up the current numbers in the IPCC report and more recent scientific literature – but you can do that yourself.”

    these are not in the IPCC report. Perhaps you or other commenters on Real Climate can direct us to the text where this information is presented. Also, as Head of Earth System Analysis, PIK I would assume you should have the answers to such fundamental questions readily available.

    On #6 you write

    “Regional changes can indeed be affected by changes in oceanic or atmospheric circulation. Predicting those is very hard though, and thus far the observed first-order picture is that you can understand the pattern of global warming (if you look at a map of temperature trends over the past hundred years or so, as shown in the IPCC reports) to a first approximation as an increase in the global mean modified by thermal inertia, i.e. greater warming over continents than the oceans, and ice/snow albedo amplification in high-latitude areas. There are some regional exceptions (e.g. cooling in the North Atlantic subpolar gyre) that may be related to circulation changes.”

    You are indicating that global warming dominates regional changes (with the few exceptions that you present). This assumption is at variance to our conclusions in

    National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp. http://www.nap.edu/openbook.php?isbn=0309095069

    where text in the Executive Summary reads

    “..the traditional global mean TOA radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes, that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change—global mean surface temperature response—while offering little information on regional climate change or precipitation. These limitations can be addressed by expanding the radiative forcing concept and through the introduction of additional forcing metrics. In particular, the concept needs to be extended to account for (1) the vertical structure of radiative forcing, (2) regional variability in radiative forcing, and (3) nonradiative forcing. A new metric to account for the vertical structure of radiative forcing is recommended…”

    “variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing. Tropospheric aerosols and landscape changes have particularly heterogeneous forcings. To date, there have been only limited studies variations of regional radiative forcing and response. Indeed, it is not clear how best to diagnose a regional forcing and response in the observational record; regional forcings can lead to global climate responses, while global forcings can be associated with regional climate responses. Regional diabatic heating can also cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing. Improving societally relevant projections of regional climate impacts will require a better understanding of the magnitudes of regional forcings and the associated climate responses.”

    and

    “Several types of forcings—most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry—impact the climate system in nonradiative ways, in particular by modifying the hydrological cycle and vegetation dynamics. Aerosols exert a forcing on the hydrological cycle by modifying cloud condensation nuclei, ice nuclei, precipitation efficiency, and the ratio between solar direct and diffuse radiation received. Other nonradiative forcings modify the biological components of the climate system by changing the fluxes of trace gases and heat between vegetation, soils, and the atmosphere and by modifying the amount and types of vegetation. No metrics for quantifying such nonradiative forcings have been accepted. Nonradiative forcings have eventual radiative impacts, so one option would be to quantify these radiative impacts. However, this approach may not convey appropriately the impacts of nonradiative forcings on societally relevant climate variables such as precipitation or ecosystem function. Any new metrics must also be able to characterize the regional structure in nonradiative forcing and climate response.”

    The paper by David Victor and Charles Kennel has opened a much needed discussion on the value of the 2C threshold as the primary metric to assess climate change.

    Roger Sr.

  27. 27

    Chris Colose – You wrote

    “But actually the whole troposphere is pretty much yoked together convectively and so you remove a degree of freedom when thinking about the vertical T profile- if you want the temperature 10 km up you can do a pretty good job predicting it from the surface T change”

    Actually there are substantive issues on the observational connection between the surface and higher in the troposphere. This was discussed in the CCSP 1.1 report, but also see

    Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., 114, D21102, doi:10.1029/2009JD011841. http://pielkeclimatesci.wordpress.com/files/2009/11/r-345.pdf

    Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2010: Correction to: “An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., 114, D21102, doi:10.1029/2009JD011841”, J. Geophys. Res., 115, D1, doi:10.1029/2009JD013655. http://pielkeclimatesci.wordpress.com/files/2010/03/r-345a.pdf

    The abstract reads

    “This paper investigates surface and satellite temperature trends over the period from 1979 to 2008. Surface temperature data sets from the National Climate Data Center and the Hadley Center show larger trends over the 30-year period than the lower-tropospheric data from the University of Alabama in Huntsville and Remote Sensing Systems data sets. The differences between trends observed in the surface and lower-tropospheric satellite data sets are statistically significant in most comparisons, with much greater differences over land areas than over ocean areas. These findings
    strongly suggest that there remain important inconsistencies between surface and satellite records.”

    While, as you correctly noted, there is a convective linkage, the observations that make up the data sets used to diagnose this connection have remaining observational quality issues.

    Roger Sr.

  28. 28
    Steven Sullivan says:

    “Stefan wrote me and was annoyed and said it was his custom to introduce people according to their discipline, and he suggested that his introduction of us was quite in line with what he does normally.” — what D&C claim Stefan wrote

    “That of course was neither said nor was it my intention at all – as a working scientist, and for a science blog, I think it is entirely normal to introduce people by the research area they have worked in, and to ignore titles, administrative positions held etc.’ — what Stefan wrote

    I note a difference.

  29. 29
    Carl Campbell says:

    Goals, targets and benchmarks are three different concepts. There is just one critical goal, which is to stop and then reverse the planet’s thermal disequalibrium. That will stop the ocean from heating and eventually allow it to cool. Doing so, and nothing else, will cause a turnaround in air temperatures. The targets and benchmarks relate to how quickly you wish to achieve this goal, and that depends on how much risk you are willing to accept, which in turn means you must be able to accurately assess the risks that are already embedded, none too easy a task. I personally think Kevin Anderson has it right. Check him out, and please tell me I’m wrong.

  30. 30
    Chris Dudley says:

    Stefan (#13),

    In models considered here in discussion, global surface temperature stops rising pretty much immediately after the abrupt cessation of greenhouse gas emissions. One model shows a brief warming bump which may be partly attributed to the simultaneous cessation of aerosol emissions. An important thing to consider is that the concentration of carbon dioxide in the atmosphere falls pretty rapidly for a short period when emissions are suddenly ended. This reduces GHG forcing. Cooling does not ensue in all models, but ongoing warming seems to only be seen in models where emissions end at 4 times the preindustrial carbon dioxide concentration or greater. For our situation, the global surface temperature would either fall or hold steady.

    Models that continue emissions in a manner that reaches a concentration stabilization level (eg. 450 ppm) do exhibit “inertia” in the sense that the global surface temperature continues to rise towards the climate sensitivity temperature appropriate for that concentration.

  31. 31
    SecularAnimist says:

    The only policy target that matters is to end the ongoing increase in CO2 emissions and begin steep reductions as soon as possible — within a few years at the very most.

    That’s not at all hard to do, technologically or economically — indeed even apart from global warming itself, the technological, economic, social and environmental benefits are huge and the costs are trivial.

    The only real obstacle is the entrenched wealth and power of the fossil fuel interests, who do not want to see five trillion dollars in wealth transferred from the fossil fuel industry to other sectors of the industrial economy.

  32. 32
    Jim Baird says:

    “The only reason why ocean heat uptake does have an impact is the fact that it is highly concentrated at the surface.”

    It is concentrated there because warm water is less dense than cold. The second law of thermodynamics dictates that heat moves to a cold sink however and the destination of least resistance for tropical heat is the poles where it melts the icecaps.

    Cyclones are often the transport mechanism for this movement and they and sea level rise have been identified by the IPCC as the greatest risks of climate change.

    Heat pipes can bypass the physical resistance to benign heat movement into the deep because they utilize phase changes of a working fluid to move heat from the high pressure evaporator end of the pipe to the low pressure condensing end where the latent heat of condensation is dispersed into the cold sink. It takes seconds to move surface heat to an ocean depth of 1000 meters whereas it takes as long as 350 years to diffuse there naturally. By placing a turbine hooked to a generator in the vapor stream mechanical and electrical energy can be produced.

    Estimates are the oceans have the potential to produce between 14 and 25 terawatts of power with ocean thermal energy conversion.

    Due to the low thermal dynamic efficiency of this process, resulting from the small temperature difference between the tropical surface and ocean water at 1000 meters, approximately 20 times more heat has to be moved than power extracted from the system. To produce 14 TW of power therefore 14 TWh would be converted and an additional 280 TWh would be moved to the depths.

    A 2010 NOAA study estimated the oceans are accumulating 330 TWh each year so virtually all of this could be moved to the deep where it “would have virtually zero impact” or be converted to productive use.

    The coefficient of expansion of sea water at 1000 meters is half that of the tropical surface thus there is an additional sea level benefit from this process over and above the short-circuiting of heat movement towards the poles. Due to the negligible temperature increase of the water at depth there would be little change in the density of the water so it would take many years for the heat to migrate back to the surface. A paper submitted to the 2012 American Geophysical Union conference by Norm Rogers, suggests the rate of diffusion is about 4 meters/year.

    Ocean heat storage may be a lousy policy target but it is a sound climate strategy because forced deep ocean hat storage makes possible the replacement of all carbon emitting fuels and thus the ultimate recovery of the atmosphere to pre-industrial greenhouse gas levels.

    As James Hansen et al. put it in the 2010 paper Earth’s energy imbalance and implications – “The rate of ocean heat uptake determines the planetary energy imbalance, which is the most fundamental single measure of the state of Earth’s climate.”

  33. 33
    Jim Baird says:

    Hank Roberts at 22 and 23, to move mid-ocean generated power to shore requires the conversion of electrical energy to an energy carrier like hydrogen. A Lawrence Livermore group lead by Greg Rau has discovered and demonstrated an ocean water electrolysis technique that removes and stores atmospheric carbon dioxide while generating carbon-negative hydrogen and produces alkalinity that can be used to offset ocean acidification. https://www.llnl.gov/news/newsreleases/2013/May/NR-13-05-07.html

    Rather than just hydrogen and oxygen production, electrolysis of ocean water produces two additional streams. One is alkaline and reacts to neutralize ocean acidity through the production of sodium carbonate and bicarbonate. The other is acidic which can be captured to react with silicate minerals to mimic natural chemical weathering of rock. This insures the carbon dioxide captured by the formation of the carbonates and bicarbonates remains permanently sequestered.

    There are a lot of climate wins encompassed in the combination of this technique with heat pipe ocean thermal energy conversion.

  34. 34
    Rod B says:

    SecularAnimist, it’s been a while and maybe old hat but I can’t let it pass. I find it hard to believe you still discard tremendous economic, sociological and technical upheavals with a simple flip of the wrist. Though those enormous struggles don’t matter much if the real goal is the pure and simple marxist redistribution of wealth as you imply.

  35. 35
    Eli Rabett says:

    Victor misses the point. A basket of goals means incessant goal shopping. He, a political scientist, should know that simply stated policy goals are defining. A basket of goals is a mess and a > 2C global temperature rise will be a disaster, actually several.

  36. 36

    Given the futility of a 2 degree limit, and the lack of economic alternatives to fossil fuels maybe you would consider geoengineering to sequester CO2 in the ocean as a potential solution? If this doesn’t get attention I’m afraid you will get nowhere.

  37. 37

    Sea level rise, the ultimate wrecker of coastal cities, beaches, estuaries and harbors will continue for centuries, as the ocean heat content continues to rise. Thermal expansion of sea water is a direct consequence of increasing heat content. The consequences of global warming will mount long after the level of atmospheric CO2 stabilizes. This post neglects to mention that reality.

  38. 38
    Alan Millar says:

    Whether you agree with Stefan or not, on whether OHC should be the measure of global warming, the fact is, if the meme is that most of the additional energy is going into the oceans then there is absolutely no need to worry about CAGW caused by burning of fossil fuels. This additional energy can only re-emerge over a period counted in thousands of years, as Stefan has pointed out.

    No matter what the debate is about ‘Peak Oil’ this is never going to extend beyond a few hundred years and the issue of Mankind voluntarily giving up their use becomes a non issue.

    Alan

  39. 39

    #29–Chris D.–Yes, but Stefan wrote: “It thus is a measure of the further global warming that we are committed to even if we do not increase the forcing any further but keep it constant.”

    Constant RF wouldn’t result from ‘an abrupt cessation of emissions.’

  40. 40
    marcus says:

    #37 Alan Millar, i think it is not that easy. “The meme” aka object of research interest is that there is, currently, a gobal pattern at work that transports most of the warming into the oceans, which is a potential explanation for the so called hiatus.
    This is a manifestation of internal variability and it does not contradict what GCM runs do explain, even older ones.
    Looking at longer timescales the temperature records, palaeoclimatology and models tell that this mechanisms are lagged, i.e. CO2 as well as temperature build up faster on the surface than the oceans can carry them away.
    I would prefer looking at this another way, the negative feedbacks provided by the oceans are those that give reasonable CO2 mitigation a chance.

    All the best

  41. 41
    Ken Fabian says:

    When it comes to communicating the ongoing nature of human disruption to the climate system I think OHC is a valuable tool, important because of the widespread use of the shorter term decade to decade variabiity of SAT’s to promote misunderstadings. In a world where political leadership is well informed about the climate problem and strongly committed to dealing with it these arguments would be mostly moot – or something for technical experts. If climate science denial and obstructionism was not rife it wouldn’t matter.

    Seems fairly obvious to me that air temperatures are strongly effected by sea surface temperatures and those are strongly effected by ocean circulations and oscillations, thus the ‘hiatus’, which can only be a temporary issue and shortlived problem – but one that has arisen during a crucial period when establishing political commitment is greatly needed and leadership is wavering.

  42. 42
    MARodger says:

    Roger A. Pielke Sr @24
    You say:-

    “While there is a lag in the global average surface temperature response, no such lag is involved in this relationship between global average radiative imbalance and ocean heat changes. This is a major advantage of using ocean heat content changes as the primary metric to diagnose global warming and to communicate this aspect of climate to policy makers.”

    While it is true that the relationship between dOHC & ERB (=the TOA imbalance) is a strong one, with over a decade of CERES data we should be aware that ERB (and thus dOHC) is as wobbly as the surface temperature record. The rolling annual average of that ERB record exibits wobbles of more than 1Wm^-2. And OHC (0-2000m) has shown a staggering rise over the last few years. Happilty it is not a million miles from what you’d expect given the wobbles. From Levitus 2000m, thirty-month averages give the following trends (per total global area with start years shown)
    2009 . 0.50+/-0.37Wm^-2
    2010 . 0.79+/-0.48Wm^-2
    2011 . 1.08+/-0.51Wm^-2
    Add to this wobble problem the point made in the #2 Response @5 (the ERB imbalance only measures pipe-line warming and does not show the no “already” warming) and it is most clear to me that ERB imbalance as a measure of AGW doesn’t cut the mustard.

  43. 43
    marcus says:

    #24 Roger:

    I have to admit I am really confused here. You cite Stefan

    […]
    “The radiative imbalance is a measure of the disequilibrium caused by the fact that (mainly) the ocean has not yet caught up with the recent increase in forcing. It thus is a measure of the further global warming that we are committed to even if we do not increase the forcing any further but keep it constant. It is not a measure of the global warming that is already observed.”
    […]

    and then You write

    […]

    This is an incorrect description of the physics.

    The change in Joules in the ocean can be directly used to diagnose the global average radiative imbalance at the top of the atmosphere over the time period of the change. There is no further warming if the oceans stopped increasing in Joules [neglecting any smaller part associated with ice melting, soil etc].
    […]

    What both of you express seems completely identical to me. I can’t figure out any difference. If there is a displacement of equilibrium on the ground, there will be a displacement at TOA radiation, given enough time and the oceans are in equilibrium with a given forcing, there will be no more disequilibrium in TOA radiation.

    All the best

  44. 44

    marcus – re #42,

    If we can diagnose the current value of global ocean heat content and the value of ocean heat content some time ago (i.e. any two time slices) with sufficient spatial and temporal accuracy, we can obtain a good estimate of the global average TOA radiative imbalance over this time period.

    This is a more robust way to obtain the radiative imbalance since we are analyzing an integral property of the climate system rather than difference of fluxes at the TOA.

    If Stefan agrees with this, I look forward to his clear confirmation of this.

    Regards

    Roger Sr.

  45. 45
    Chris Dudley says:

    Kevin (#38),

    I was responding to #13 where he does discuss cessation of emissions. I agree with your point on stabilized radiative forcing (his response in #5).

  46. 46
    SecularAnimist says:

    Rod B wrote: “… if the real goal is the pure and simple marxist redistribution of wealth as you imply.”

    I said NOTHING WHATSOEVER about any “marxist redistribution of wealth”.

    When the death-grip of the fossil fuel corporations on energy and economic policy is broken, markets will “redistribute” wealth to those who provide new and better energy technologies very efficiently.

    So spare me the hackneyed red-baiting nonsense.

  47. 47

    Roger,
    If we can diagnose the current value of global ocean heat content and the value of ocean heat content some time ago (i.e. any two time slices) with sufficient spatial and temporal accuracy, we can obtain a good estimate of the global average TOA radiative imbalance over this time period.

    As with Marcus, I’m partly confused by how what you and Stefan say is different. If you consider the change in OHC over some time interval then you can get the average rate at which energy accrued in the oceans over that time interval. Since the oceans are the dominant heat sink, this is then a reasonable estimate for the average system heat uptake rate over that time interval. If we could take an arbitrarily small time interval, then we could determine (as Stefan indicated in his response to you) the disequilibrium of the system today (i.e., the rate at which we are still accruing energy after a change in radiative forcing and a subsequent change in temperature). However, since the measurements are intrinsically variable, we would typically consider a sufficiently long time interval so as to average over this variability. If this time interval were reasonably short (a decade say), though, this would still be a measure of the current disequilibrium of the system.

    So, I’m not sure what you’re getting at with this

    This is a more robust way to obtain the radiative imbalance since we are analyzing an integral property of the climate system rather than difference of fluxes at the TOA.
    If we consider a sufficiently long time interval then this would be a very poor indicator of the current radiative imbalance. For example, if we consider a scenario in which we have a change in radiative forcing and then let the system equilibrate, the average rate of change of the OHC would be non-zero even when the system were in equilibrium. To estimate the current radiative imbalance we would ideally want to use as short a time interval as possible, but not so short that we are dominated by variability.

  48. 48
    Aaron Lewis says:

    The oceans are BIG. They do not respond to small, short term policy. They require big, long term policies.

    A small, short term policy may jiggle the atmospheric (forcing), but that does not change the fact that in the long run we need policies that are smart enough, big enough, and tough enough to deal with the issues of ocean heat content.

    Arctic Sea ice in 2007, told us that the equilibriums between the oceans and the ice had changed more than expected by the global climate models. First, we need to think deeper and farther ahead, so that we are ready for such surprises. Then we need to be proactive, so that we avoid such surprises in the distant future.

    The weather of AGW is coming at us faster than the models projected. And it is always the weather that causes damage. We can engineer for climate, but the weather is always what bites. In a time of global warming the probability distribution functions for extreme weather are highly skewed, with long, fat tails on the warm side.

    Such long, fat tails are clubs that tend to break rational engineering and conventional policy negotiation. This is not like any problem before us in the last 3 million years. We are not adapted to such problems. We need to think, talk, and listen. Mostly, it is in the listening skills where we fail.

  49. 49
    Hank Roberts says:

    > If we can ... this is

    Correcting the verb tense, that should read

    If we could ... this would be

    “But as it isn’t, it ain’t.”

  50. 50
    Eli Rabett says:

    Roger Pielke Sr. writes:

    If we can diagnose the current value of global ocean heat content and the value of ocean heat content some time ago (i.e. any two time slices) with sufficient spatial and temporal accuracy, we can obtain a good estimate of the global average TOA radiative imbalance over this time period.

    To which Eli Rabett replied half a decade ago and now: Good luck.

    The only metric we have that goes back far enough for policy purposes, which is what is being discussed here, is the surface temperature and precipitation records.

    The perfect is always the enemy of the good when denial of the need for change is involved.


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