The Ecconomist which until recently had been very much in the alarmist camp in the global warming debate but has recently taken a more neutral tone, has just published a chart purported to be from the forthcoming fifth assessment IPCC report. The chart shows their projections of climate sensitivity to increasing atmospheric CO2.
This is the measure used by researchers of how much they expect the world’s average temperature to increase in response to particular increases in levels of carbon dioxide in the atmosphere. According to one table from the unpublished report, which was seen by The Economist, at CO2 concentrations of between 425 parts per million and 485 ppm, temperatures in 2100 would be 1.3-1.7°C above their pre-industrial levels. That seems lower than the IPCC’s previous assessment, made in 2007. Then, it thought concentrations of 445-490 ppm were likely to result in a rise in temperature of 2.0-2.4°C.Here is the chart
Given that the IPCC and other global warmists use 280 ppm as the "pre-industrial" level of atmospheric CO2, an actual doubling by their hypothesis will happen when CO2 reaches the 560 ppm level . So if this chart is their actual projection, a doubling of CO2 "from pre-industrial" levels will now cause a warming of between 2.0-2.4 deg C.
Note that the two figures that have been so much a part of the global warming narrative are starting to come into sink. First is the arbitrary "doubling of CO2" which has been the great Cassandra of the warmist for so many years and the more recent goal set in Copenhagen in 2009 to keep temperatures at a two degree rise globally. What a coincidence that once a political goal was set, the science followed.
