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Can 2°C warming be avoided?

Filed under: — group @ 31 January 2006 - (Français)

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.
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Hansen in the New York Times

Filed under: — gavin @ 29 January 2006

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.
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Calculating the greenhouse effect

Filed under: — gavin @ 21 January 2006

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). More »

Daily Kos interview

Filed under: — group @ 20 January 2006

A brief welcome to anyone coming over from Daily Kos today. Three of us (Mike, Gavin and Stefan) are interviewed by DarkSyde on climate change, this site and walking the line between science and politics. To find something specific, check out the Highlights on the side bar, the index, or use the search bar above.

Atlantic circulation change summary

Filed under: — gavin @ 19 January 2006 - (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. More »