Prof. Richard Lindzen (MIT) is often described as the most respectable of the climate ‘sceptics’ and is frequently cited in discussions here and elsewhere. Lindzen clearly has many fundamentally important papers under his belt (work on the QBO and basic atmospheric dynamics), and a number of papers that have been much less well received by the community (the ‘Iris’ effect etc.). Last year, he gave evidence to and answered questions from, a UK House of Lords Committee investigating the economics of climate change, in which he discoursed freely on the science. I’ll try here to sort out what he said. [Read more…] about Richard Lindzen’s HoL testimony
Greenhouse gases
James Lovelock’s Gloomy Vision
James Lovelock, renegade Earth scientist and creator of the Gaia hypothesis, has written a gloomy new book called “Revenge of Gaia”, in which he argues that we should be stashing survival manuals, printed on good old-fashioned paper, in the Arctic where the last few breeding pairs of humans will likely be found after a coming climate catastrophe. The book is not published in the U.S. yet, but it is available from amazon.co.uk. Lovelock has never been one to shrink from a bold vision. What is it he sees now?
Can 2°C warming be avoided?
Guest comment by Malte Meinshausen, Reto Knutti and Dave Frame
Yesterday’s BBC article on the “Avoiding Dangerous Climate Change” report of the Exeter meeting last year, carried two messages that have left some a little confused. On the one hand, it said that a stabilization of greenhouse gases at 400-450 ppm CO2-equivalent concentrations is required to keep global mean warming below 2°C, which in turn is assumed to be necessary to avoid ‘dangerous’ climate change. On the other hand, people are cited saying that “We’re going to be at 400 ppm in 10 years’ time”.
So given that we will exceed 400 ppm CO2 in the near future, is a target of 2°C feasible? To make a long story short: the answer is yes.
[Read more…] about Can 2°C warming be avoided?
Hansen in the New York Times
The more astute of you may have noticed the headline NYT story this weekend on Jim Hansen’s ongoing tussles with the (politically appointed) public affairs people at NASA HQ (Jim is my immediate boss so you need to read this with that in mind!). Most of the recent fuss has been about the GISS analysis of surface air temperatures (GISTEMP), which used to routinely be made available as soon as the analysis was done (usually a week or so after the end of any particular month). This data was generally released with little or no fuss (and no press releases) except for the end of year summary. However, as it started to become clearer that 2005 was a contender for warmest year, journalists and others started paying direct attention to the raw figures and writing stories that were bypassing public affairs. For instance, Juliet Eilperin’s October story in WaPo (discussed here and here) was one of the stories that they were most definitely not happy with (as alluded to in today’s WaPo). No follow-up media requests to interview relevant scientists were approved.
[Read more…] about Hansen in the New York Times
Calculating the greenhouse effect
In another forum (on a planet far, far away), the following quote recently came up:
….the combined effect of these greenhouse gases is to warm Earth’s atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity8.
We’ve discussed the magnitude of the greenhouse effect before, but it might be helpful to step through this ‘back-of-the-agenda’ calculation and see what the numbers really give. (Deltoid has also had a go at some of these mis-statements). [Read more…] about Calculating the greenhouse effect
Scientists baffled!
Every so often a scientific paper comes out that truly surprises. The results of Keppler et al in Nature this week is clearly one of those. They showed that a heretofore unrecognised process causes living plant material to emit methane (CH4, the second most important trace greenhouse gas), in quantities that appear to be very significant globally. This is surprising in two ways – firstly, CH4 emission is normally associated with anaerobic (oxygen-limited) environments (like swamps or landfills) but chemistry in plants is generally thought of as ‘aerobic’ i.e. not oxygen-limited, and secondly, because although the total budget for methane has some significant uncertainty associated with it (see the IPCC assessment here), the initial estimates of this effect (between 62–236 Tg/yr out of a total source of 500+ Tg/yr!) give numbers that might be difficult to incorporate without some significant re-evaluations elsewhere.
Reactions so far have been guarded, and there will undoubtedly be a scramble to check and refine the estimates of this process’s importance. Once the dust settles though, the situation may not be so different to before – some emissions may turn out to have been mis-identified, this source may not be as large as these initial estimates (10-30% of total sources) suggest, or it might radically challenge our current understanding of methane’s sources and sinks. However, the process by which this is decided will demonstrate clearly that the scientific method is alive and well in the climate sciences. That is, as long as a work is careful and the conclusions sound, papers that upset the apple cart can appear in the major journals and have a good chance of ending up being accepted by the rest of the field (providing the conclusions hold up of course!).
Update 19 Jan: The authors of the study have released a clarification of their study to counter some of the misleading conclusions that had appeared in the press.
Polar Amplification
Guest commentary by Cecilia Bitz, University of Washington
“Polar amplification” usually refers to greater climate change near the pole compared to the rest of the hemisphere or globe in response to a change in global climate forcing, such as the concentration of greenhouse gases (GHGs) or solar output (see e.g. Moritz et al 2002). Polar amplification is thought to result primarily from positive feedbacks from the retreat of ice and snow. There are a host of other lesser reasons that are associated with the atmospheric temperature profile at the poles, temperature dependence of global feedbacks, moisture transport, etc. Observations and models indicate that the equilibrium temperature change poleward of 70N or 70S can be a factor of two or more greater than the global average. [Read more…] about Polar Amplification
Naturally trendy?
From time to time, there is discussion about whether the recent warming trend is due just to chance. We have heard arguments that so-called ‘random walk‘ can produce similar hikes in temperature (any reason why the global mean temperature should behave like the displacement of a molecule in Brownian motion?). The latest in this category of discussions was provided by Cohn and Lins (2005), who in essence pitch statistics against physics. They observe that tests for trends are sensitive to the expectations, or the choice of the null-hypothesis .
Natural Variability and Climate Sensitivity
One of the central tasks of climate science is to predict the sensitivity of climate to changes in carbon dioxide concentration. The answer determines in large measure how serious the consequences of global warming will be. One common measure of climate sensitivity is the amount by which global mean surface temperature would change once the system has settled into a new equilibrium following a doubling of the pre-industrial CO2 concentration. A vast array of thought has been brought to bear on this problem, beginning with Arrhenius’ simple energy balance calculation, continuing through Manabe’s one-dimensional radiative-convective models in the 1960’s, and culminating in today’s comprehensive atmosphere-ocean general circulation models. The current crop of models studied by the IPCC range from an equilibrium sensitivity of about 1.5°C at the low end to about 5°C at the high end. Differences in cloud feedbacks remain the principal source of uncertainty. There is no guarantee that the high end represents the worst case, or that the low end represents the most optimistic case. While there is at present no compelling reason to doubt the models’ handling of water vapor feedback, it is not out of the question that some unanticipated behavior of the hydrological cycle could make the warming somewhat milder or on the other hand, much, much worse. Thus, the question naturally arises as to whether one can use information from past climates to check which models have the most correct climate sensitivity.
[Read more…] about Natural Variability and Climate Sensitivity
Methane hydrates and global warming
There is an enormous amount of methane (CH4) on earth frozen into a type of ice called methane hydrate. Hydrates can form with almost any gas and consist of a ‘cage’ of water molecules surrounding the gas. (The term ‘clathrate’ more generally describes solids consisting of gases are trapped within any kind of cage while hydrate is the specific term for when the cage is made of water molecules). There are CO2 hydrates on Mars, while on Earth most of the hydrates are filled with methane. Most of these are in sediments of the ocean, but some are associated with permafrost soils.
Methane hydrates would seem intuitively to be the most precarious of things. Methane hydrate melts if it gets too warm, and it floats in water. Methane is a powerful greenhouse gas, and it degrades to CO2, another greenhouse gas which accumulates in the atmosphere just as fossil fuel CO2 does. And there is a lot of it, possibly more than the traditional fossil fuel deposits. Conceivably, climate changes could affect these deposits. So what do we know of the disaster-movie potential of the methane hydrates?