Climate sensitivity to CO2 probed

[killadoob]

Global temperatures could be less sensitive to changing atmospheric carbon dioxide (CO2) levels than previously thought, a study suggests.

The researchers said people should still expect to see "drastic changes" in climate worldwide, but that the risk was a little less imminent.

The results are published in Science.

Previous climate models have used meteorological measurements from the last 150 years to estimate the climate's sensitivity to rising CO2.

From these models, scientists find it difficult to narrow their projections down to a single figure with any certainty, and instead project a range of temperatures that they expect, given a doubling of atmospheric CO2 from pre-industrial levels.

The new analysis, which incorporates palaeoclimate data into existing models, attempts to project future temperatures with a little more certainty.

Lead author Andreas Schmittner from Oregon State University, US, explained that by looking at surface temperatures during the last Ice Age - 21,000 years ago - when humans were having no impact on global temperatures, he, and his colleagues, show that this period was not as cold as previous estimates suggest.

"This implies that the effect of CO2 on climate is less than previously thought," he explained

By incorporating this newly discovered "climate insensitivity" into their models, the international team was able to reduce their uncertainty in future climate projections.

The new models predict that given a doubling in CO2 levels from pre-industrial levels, the Earth's surface temperatures will rise by 1.7 to 2.6 degrees C.

That is a much tighter range than suggested by the Intergovernmental Panel on Climate Change (IPCC)'s 2007 report, which suggested a rise of between 2 to 4.5 degrees C.

The new analysis also reduces the expected average surface temperatures to just over 2 degrees C, from 3.

The authors stress the results do not mean threat from human-induced climate change should be treated any less seriously, explained palaeoclimatologist Antoni Rosell-Mele from the Autonomous University of Barcelona, who is a member of the team that came up with the new estimates.

But it does mean that to induce large-scale warming of the planet, leading lead to widespread catastrophic consequences, we would have to increase CO2 more than we are going to do in the near future, he said.

"But we don't want that to happen at any time, right?"

"At least, given that no one is doing very much around the planet [about] mitigating CO2 emissions, we have a bit more time," he remarked.

http://www.bbc.co.uk/news/science-environment-15858603

 

[bekdik]

http://scienceandpublicpolicy.org/monckton/greenhouse_warming_what_greenhouse_warming_.html

The observational and experimental graphs reproduced here contain between them a dozen different observed-temperature datasets, not one of which exhibits the “hot-spot” signature of anthropogenic “greenhouse warming” that is predicted by the computer models upon which the UN so heavily relies. In every one of these datasets, the trend in the troposphere is no greater, and generally smaller, than the trend near the surface. According to Spencer et al. (2007), the tropospheric temperature trend is now 0.05 ± 0.07 degrees Celsius per decade. Therefore, the contribution of the anthropogenic enhancement of the greenhouse effect to surface warming is somewhere between -0.02 and 0.12 degrees Celsius per decade, with a central estimate of 0.5 degrees Celsius, or approximately one-sixth of the UN’s central estimate of 3 degrees Celsius for a doubling of atmospheric carbon dioxide concentration.

This result is broadly consistent with that of Schwartz (2007), who supports the conclusions of Lindzen (2006), calculating by entirely different methods that the temperature increase to be expected from a doubling of atmospheric carbon dioxide concentration will be one-half to one-third of the UN’s central estimate.

Can the discrepancy between prediction and observation be explained, as the CCSP suggests, by uncertainties in the observed data? The very close correlation between anomalies in tropical outgoing long-wave radiation and anomalies in global lower-troposphere temperatures, taken with the near-total absence of correlation between monotonic increases in CO2 concentration and chaotic temperature anomalies, suggests that it is the computer models, not real-world observations that are likely to be at fault. Ultimately this question can only be resolved by collecting further data: but the CCSP’s predisposition in favor of theoretical modeling and against the results of direct observation is commonplace among official climate-science bodies. Or does the discrepancy arise because the predictions are carried through to equilibrium climate response, while the observations are perforce carried only to a transient response? Professor Lindzen comments that this failure of observation to match prediction cannot be so easily explained, since the transient response would be likely to exceed the equilibrium response. He concludes that no more than about a third of the observed trend at the surface is likely to be due to greenhouse warming, and adds: “This is about as close as one ever gets to proof in climate physics.”

On this analysis, “global warming” is unlikely to be dangerous and extremely unlikely to be catastrophic.

 

[bekdik]

An interesting analysis: http://wattsupwiththat.com/2010/04/25/predictions-of-global-mean-temperatures-ipcc-projections/