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about Gavin Schmidt

Gavin Schmidt is a climate modeler, working for NASA and with Columbia University.

Calculating the greenhouse effect

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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

Atlantic circulation change summary

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Translations: (Français)

Nature this week has an excellent summary of the state of the science with regards to possible changes in the ocean thermohaline (or meridional) circulation in the Atlantic and its impact on climate. Even though it quotes a couple of us, it’s still worth reading if you want to understand how results like the Bryden et al paper – that suggested that the Atlantic overturning had reduced by 30% in recent decades – are assimilated into the scientific picture. [Read more…] about Atlantic circulation change summary

Scientists baffled!

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Translations: (Français)

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.

How to be a real sceptic

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Scepticism is often discussed in connection with climate change, although the concept is often abused. I therefore thought it might be interesting to go back and see what the epitome of 20th Century sceptics, Bertrand Russell, had to say on the subject. This is extracted from the Introduction to his ‘Sceptical Essays’ (1928):
[Read more…] about How to be a real sceptic

Climate meeting blogging

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Two climate-related meetings are being covered quite extensively this week, the American Geophsyical Union meeting in San Francisco is being blogged for Woods Hole Oceanographic Institution, and the COP/MOP meeting in Montreal is being podcasted by the New York Times and blogged by other attendees. Hopefully this is a sign that scientists are starting to use these tools more effectively than they have so far.

Debate over the Early Anthropogenic Hypothesis

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There have been a few mentions of the ‘early anthropocene’ hypothesis recently (cf. the EPICA CO2 results, and Strange Bedfellows). We therefore welcome Bill Ruddiman to RealClimate to present his viewpoint and hopefully stimulate further discussion – gavin.

[Addendum: For a non-technical backgrounder on the ‘early anthropocene’ hypothesis and its significance in the context of anthropogenic climate change, see Bill Ruddiman’s article “How Did Humans First Alter Global Climate?” from the March 2005 issue of “Scientific American” (first two paragraphs available for free; full article must be purchased). -mike]

Guest posting from Bill Ruddiman, University of Virginia

The hypothesis (Ruddiman, 2003) that early agriculture caused large enough emissions of greenhouse gases millennia ago to offset a natural climatic cooling remains controversial. The centerpiece of the hypothesis was a comparison of the increases of CO2 and CH4 values in Vostok ice during the current (Holocene) interglaciation versus the (natural) drops during similar portions of the three previous interglaciations. [Read more…] about Debate over the Early Anthropogenic Hypothesis

650,000 years of greenhouse gas concentrations

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Translations: (Français)

The latest results from the EPICA core in Antarctica have just been published this week in Science (Siegenthaler et al. and Spahni et al.). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have now been analysed for greenhouse gas concentrations saved in tiny bubbles. The records for CO2, CH4 and N2O both confirm the Vostok records that have been available for a few years now, and extend them over another 4 glacial-interglacial cycles. This is a landmark result and a strong testament to the almost heroic efforts in the field to bring back these samples from over 3km deep in the Antarctica ice. So what do these new data tell us, and where might they lead? [Read more…] about 650,000 years of greenhouse gas concentrations

Update on 2005 temperatures

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Translations: (Français)

Further to our post about whether 2005 will be a year of record warmth, Jim Hansen has put out a brief discussion on the Washington Post report and some of the subsequent discussion. One minor clarification to his statements is that the reporter involved (Juliet Eilperin) did in fact leave messages for the relevant people at GISS (including me) prior to publication, but sometimes people can just be difficult to track down. Oh….and for those who are counting, with the preliminary October data in, 2005 has pulled ahead of 1998 in both the GISS land based met. station index (0.76 to 0.73°C) and the GISS land-ocean index (0.59 to 0.58°C). All previous caveats still apply….

Lawson vs. the IPCC

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Nigel Lawson, one of Britain’s Chancellors of the Exchequer during the Thatcher Era (Secretary of the Treasury for those needing a US translation) and more recently known as the father of Nigella Lawson (a UK cooking diva), has weighed into the climate debate with a recent broadside calling for the abolition of the IPCC (Intergovernmental Panel on Climate Change). Based on a curious report by the UK House of Lords Economics Affairs committee (in which they made clear that they had no scientific expertise), Lawson demands that the only global scientific assessment process on climate change be shut down, and replaced with ….well what exactly? [Read more…] about Lawson vs. the IPCC