Climate science from climate scientists...
) The past few weeks and years have seen a bushel of papers finding that the natural world, in particular perhaps the ocean, is getting fed up with absorbing our CO2. There are uncertainties and caveats associated with each study, but taken as a whole, they provide convincing evidence that the hypothesized carbon cycle positive feedback has begun. [Read more…] about ¿Está desapareciendo el sumidero de carbono oceánico?
There was a minor kerfuffle in recent days over claims by Tim Flannery (author of “The Weather Makers”) that new information from the upcoming IPCC synthesis report will show that we have reached 455 ppmv CO2_equivalent 10 years ahead of schedule, with predictable implications. This is confused and incorrect, but the definitions of CO2_e, why one would use it and what the relevant level is, are all highly uncertain in many peoples’ minds. So here is a quick rundown.
Definition: The CO2_equivalent level is the amount of CO2 that would be required to give the same global mean radiative forcing as the sum of a basket of other forcings. This is a way to include the effects of CH4 and N2O etc. in a simple way, particularly for people doing future impacts or cost-benefit analysis. The equivalent amount is calculated using the IPCC formula for CO2 forcing:
Total Forcing = 5.35 log(CO2_e/CO2_orig)
where CO2_orig is the 1750 concentration (278 ppmv).
Usage: There are two main ways it is used. Firstly, it is often used to group together all the forcings from the Kyoto greenhouse gases (CO2, CH4, N2O and CFCs), and secondly to group together all forcings (including ozone, sulphate aerosols, black carbon etc.). The first is simply a convenience, but the second is what matters to the planet. Many stabilisation scenarios, such as are being discussed in UNFCCC negotiations are based on stabilising total CO2_e at 450, 550 or 750 ppmv.
Magnitude The values of CO2_e (Kyoto) and CO2_e (Total) can be calculated from Figure 2.21 and Table 2.12 in the IPCC WG1 Chapter 2. The forcing for CO2, CH4 (including indirect effects), N2O and CFCs is 1.66+0.48+0.07+0.16+0.34=2.71 W/m2 (with around 0.3 W/m2 uncertainty). Using the formula above, that gives CO2_e (Kyoto) = 460 ppmv. However, including all the forcings (some of which are negative), you get a net forcing of around 1.6 W/m2, and a CO2_e (Total) of 375 ppmv with quite a wide error bar. This is, coincidently, close to the actual CO2 level.
Implications The important number is CO2_e (Total) which is around 375 ppmv. Stabilisation scenarios of 450 ppmv or 550 ppmv are therefore still within reach. Claims that we have passed the first target are simply incorrect, however, that is not to say they are easily achievable. It is even more of a stretch to state that we have all of a sudden gone past the ‘dangerous’ level. It is still not clear what that level is, but if you take a conventional 450 ppmv CO2_e value (which will lead to a net equilibrium warming of ~ 2 deg C above pre-industrial levels), we are still a number of years from that, and we have (probably) not yet committed ourselves to reaching it.
Finally, the IPCC synthesis report is simply a concise summary of the three separate reports that have already come out. It therefore can’t be significantly different from what is already available. But this is another example where people are quoting from draft reports that they have neither properly read nor understood and for which better informed opinion is not immediately available. I wish journalists and editors would resist the temptation to jump on leaks like this (though I know it’s hard). The situation is confusing enough without adding to it unintentionally.
We often get requests to provide an easy-to-understand explanation for why increasing CO2 is a significant problem without relying on climate models and we are generally happy to oblige. The explanation has a number of separate steps which tend to sometimes get confused and so we will try to break it down carefully.
[Read more…] about The CO2 problem in 6 easy steps
In a nice example of how complicated climate feedbacks and interactions can be, Sitch and colleagues report in Nature advance publication on a newly modelled effect of ground level (or tropospheric) ozone on carbon uptake on land (BBC). The ozone they are talking about is the ‘bad’ ozone (compared to ‘good’ stratospheric ozone) and is both a public health hazard and a greenhouse gas. Tropospheric ozone isn’t directly emitted by human activity, but is formed in the atmosphere as a result of photolytic reactions related to CH4, CO, NOx and VOCs (Volatile Organic Compounds like isoprene, benzene etc.) – the so-called ozone precursors.
It’s well known that increased ozone levels – particularly downwind of cities – can be harmful to plants, and in this new study with a carbon-climate model, they quantify how by how much increasing ozone levels make it more difficult for carbon to be sequestered by the land biosphere. This leads to larger CO2 levels in the atmosphere than before. Hence the ozone has, as well as its direct effect as a greenhouse gas, an indirect effect on CO2, which in this model at least appears to be almost as large.
Actually it’s even more complicated. Methane emissions are one of the principal causes of the rise of ozone, and the greenhouse effect of ozone can be thought of as an indirect effect of CH4 (and CO and VOCs). But while NOx is an ozone precursor, it actually has an indirect effect that reduces CH4, so that the net impact of NOx has been thought to be negative (i.e. the reduction in CH4 outweighs the increase of ozone in radiative forcing – see this paper for more details). This new result might prompt a re-adjustment of that balance – i.e. if the ozone produced by NOx has a stronger effect than previously thought (through this new indirect mechanism), than it might outweigh the reduction in CH4, and lead to NOx emissions themselves being a (slightly) positive forcing.
In a bizarre way this is actually good news. There are plenty of reasons to reduce NOx emissions already because of it’s impact on air pollution and smog, but this new result might mean that reductions wouldn’t make climate change any worse. It also, once again, highlights the role of CH4 (the second biggest GHG forcing), and points out a further reason (if that was required) why further methane reductions could be particularly welcome in moderating future changes in climate and air quality.
) () A guest post by Spencer Weart, in collaboration with Raymond T. Pierrehumbert
The simple physics explanations for the greenhouse effect that you find on the internet are often quite wrong. These well-meaning errors can promote confusion about whether humanity is truly causing global warming by adding carbon dioxide to the atmosphere. Some people have been arguing that simple physics shows there is already so much CO2 in the air that its effect on infrared radiation is "saturated"— meaning that adding more gas can make scarcely any difference in how much radiation gets through the atmosphere, since all the radiation is already blocked. And besides, isn’t water vapor already blocking all the infrared rays that CO2 ever would?
At Jim Hansen’s now famous congressional testimony given in the hot summer of 1988, he showed GISS model projections of continued global warming assuming further increases in human produced greenhouse gases. This was one of the earliest transient climate model experiments and so rightly gets a fair bit of attention when the reliability of model projections are discussed. There have however been an awful lot of mis-statements over the years – some based on pure dishonesty, some based on simple confusion. Hansen himself (and, for full disclosure, my boss), revisited those simulations in a paper last year, where he showed a rather impressive match between the recently observed data and the model projections. But how impressive is this really? and what can be concluded from the subsequent years of observations?
[Read more…] about Hansen’s 1988 projections
) () There are a few minor items this week worthy of mention:
1. The CO2 rise. Who dunnit?
Here at RealClimate, we have been (naively, apparently) operating under the assumption that climate change contrarians had long ago moved on from the untenable position that humans are not even responsible for the observed increase in CO2 concentrations over the past two centuries. The dubious paper by Ernst Beck we commented on the other day indicates that there is indeed still a rear guard attack being waged. As if to drive the point home further, pundit Alexander Cockburn, known generally for his progressive views, has perplexingly disputed the existence of any link between CO2 emissions and rising CO2 concentrations in the atmosphere in a screed he penned this week for the online journal “Counterpunch” (also printed in The Nation). It’s hard to know where to start, since his piece is so over the top and gets just about everything so thoroughly wrong, it’s almost comical. So we’ll just hit the low points: (a) Cockburn claims that there is zero empirical evidence that anthropogenic production of CO2 is making any measurable contribution to the world’s present warming trend, despite the fact that not even such strident climate change contrarians as Pat Michaels dispute that there is a measurable influence of anthropogenic greenhouse gases on global temperature. Plus there’s all the empirical evidence of course (see the new IPCC report). (b) Going further, Cockburn brazenly opines that ‘it is impossible to assert that the increase in atmospheric CO2 stems from human burning of fossil fuels’ despite the fact that there is an isotopic smoking gun for this connection. He then (c) fails to understand that water vapor is a feedback not a forcing, and citing ‘expert’ Dr. Martin Hertzberg, quite remarkably states that ‘It is the warming of the earth that is causing the increase of carbon dioxide and not the reverse.’ Never mind that isotopic evidence proves otherwise. Upon what evidence does he base this assertion?
Since no anti-global warming op-ed these days is complete without it, Cockburn (d) resorts to the usual misrepresentation of lag/lead relationships between CO2 and temperatures during glacial/interglacial cycles as if they disprove the causal relationship between greenhouse gas concentrations and surface temperatures (see our most recent debunking of this favorite contrarian talking point here). Oh dear.
2. The other (Glenn) Beck–Even Worse!
CNN gave their resident shock-jock Glenn Beck a forum for spreading more disinformation on global warming in an hour-long segment entitled Exposed: The Climate of Fear (see also this discussion by “Media Matters”). We could pick apart his (rather thin) arguments, which constitute the usual cocktail of long debunked contrarian talking points. Suffice it to say, however, that the moment a rhetorician invokes Hitler, Nazi Germany, and Eugenics, it is the moment they are no longer worthy of being listened to (cf Godwin’s Law of usenet debates). We don’t seem to be alone in our opinion here. Beck’s performance earned him the dubious title of “worst person in the world” from analyst Keith Olbermann.
However, there was one amusing moment: Beck asked Christopher ‘Incorrect’ Horner what the key thing to google was that would show that Al Gore was wrong. Horner suggested the lag between CO2 and temperature in the ice cores. Of course, if you do Google that, the first hit is the RealClimate debunking of the issue. Thanks!
3. Nature’s new blog
Nature has started a new blog called “Climate Feedback”, which says of itself ‘Climate Feedback is a blog hosted by Nature Reports: Climate Change to facilitate lively and informative discussion on the science and wider implications of global warming. The blog aims to be an informal forum for debate and commentary on climate science in our journals and others, in the news, and in the world at large.’
We wish it well, remembering their welcome for RealClimate, though early reviews based on the first few posts are decidedly mixed.
Guest commentary from Georg Hoffmann
Our understanding of the natural carbon cycle has greatly improved since the times of Svante Arrhenius (1859-1927) and Guy Stewart Callendar (1898-1964). We know what the atmospheric background value of CO2 currently is (it passed 380ppm last year, about 100ppm over the pre-industrial level), we know the seasonal/diurnal cycle in different environments, we have been able to put reasonable constraints on terrestrial and marine sources and sinks, and finally we know the impact of fuel combustion both globally and locally in heavily polluted areas.
[Read more…] about Beck to the future
) () Una traducción en español está disponible aquí
A lot of what gets discussed here in relation to the greenhouse effect is relatively simple, and yet can be confusing to the lay reader. A useful way of demonstrating that simplicity is to use a stripped down mathematical model that is complex enough to include some interesting physics, but simple enough so that you can just write down the answer. This is the staple of most textbooks on the subject, but there are questions that arise in discussions here that don’t ever get addressed in most textbooks. Yet simple models can be useful there too.
I’ll try and cover a few ‘greenhouse’ issues that come up in multiple contexts in the climate debate. Why does ‘radiative forcing’ work as method for comparing different physical impacts on the climate, and why you can’t calculate climate sensitivity just by looking at the surface energy budget. There will be mathematics, but hopefully it won’t be too painful.
[Read more…] about Learning from a simple model