Over at the Wall Street Journal, Matt Ridley reports that a leaked draft version of the UN's Intergovernmental Panel on Climate Change's forthcoming Summary for Policy Makers finds that earlier projections of future warming have likely been too high. In his column, "Dialing Back the Alarm on Climate Change," Ridley reports that according to the IPCC …
…the temperature rise we can expect as a result of man-made emissions of carbon dioxide is lower than the IPPC thought in 2007.
Specifically, the report notes that new estimates of climate sensitivity—roughly the eventual amount of warming that would expected if atmospheric carbon dioxide doubles—suggests that that there is a chance that the increase global average temperatures be as little as 1 degree Celsius. More significant are the new estimates of the rate of future warming on its way to achieving equilibrium at doubled carbon dioxide:
A more immediately relevant measure of likely warming has also come down: "transient climate response" (TCR)—the actual temperature change expected from a doubling of carbon dioxide about 70 years from now, without the delayed effects that come in the next century. The new report will say that this change is "likely" to be 1 to 2.5 degrees Celsius and "extremely unlikely" to be greater than 3 degrees. This again is lower than when last estimated in 2007 ("very likely" warming of 1 to 3 degrees Celsius, based on models, or 1 to 3.5 degrees, based on observational studies).
Most experts believe that warming of less than 2 degrees Celsius from preindustrial levels will result in no net economic and ecological damage. Therefore, the new report is effectively saying (based on the middle of the range of the IPCC's emissions scenarios) that there is a better than 50-50 chance that by 2083, the benefits of climate change will still outweigh the harm.
In addition, Ridley reports that more recent estimates of climate sensitivity from newly published peer reviewed studies are even lower than those suggested in the new IPCC report.
But, wait there's more. The Daily Mail has also gotten hold of a leaked version of the IPCC Summary and it reports that the UN climate panel admits that computer model estimates of average global temperature increases have been way too high. The Mail notes…
…the leaked report makes the extraordinary concession that the world has been warming at only just over half the rate claimed by the IPCC in its last assessment, published in 2007.
Back then, it said that the planet was warming at a rate of 0.2C every decade – a figure it claimed was in line with the forecasts made by computer climate models.
But the new report says the true figure since 1951 has been only 0.12C per decade – a rate far below even the lowest computer prediction.
The 31-page 'summary for policymakers' is based on a more technical 2,000-page analysis which will be issued at the same time. It also surprisingly reveals: IPCC scientists accept their forecast computers may have exaggerated the effect of increased carbon emissions on world temperatures – and not taken enough notice of natural variability.
This rate of warming is in line with the global average temperature increase of 0.14C per decade that the satellite data have reporting since 1979.
If the draft version of the IPCC Summary stands that would suggest that the climatologists assembled by the UN have now come to basically agree with a recent study in Nature Climate Science, which I reported last month, that the observed rate of warming has been about half of what the computer model have been projecting.
Further massaging of the IPCC Summary for Policy Makers is currently under way and the final version will be released on September 27. Stay tuned.
H/T to Johnny Longtorso on Ridley even though I saw the Ridley article a couple of days ago. Forestalls unwarranted wounded feelings.