IPCC Plays Down Climate Sensitivity
The Intergovernmental Panel on Climate Change has downplayed evidence that the global climate is considerably less sensitive to greenhouse gases than climate models are estimating, a new paper says.
Published by Britain’s Global Warming Policy Foundation think tank, the new paper says clues to weaker climate sensitivity have all been referred to in the IPCC’s recently published Fifth Assessment Report.
“However, this important conclusion was not drawn in the full IPCC report, it is only mentioned as a possibility, and is ignored in the IPCC’s Summary for Policymakers,” the report says.
The report was written by independent British climate scientist Nic Lewis and Dutch science writer Marcel Crok. Both were expert reviewers of the IPCC report, and Lewis was an author of two papers cited in it.
In a foreword to their report published by the foundation, respected US climate scientist Judith Curry says the sensitivity of the climate to increasing concentrations of carbon dioxide is at the heart of the scientific debate on anthropogenic climate change, and also the public debate on the appropriate policy response to increasing carbon dioxide in the atmosphere.
“Climate sensitivity and estimates of its uncertainty are key inputs into the economic models that drive cost-benefit analyses and estimates of the social cost of carbon,” Dr Curry said.
The Lewis and Crok report says that for more than 30 years climate scientists have presented a range for climate sensitivity that remains largely unchanged at 1.5C to 4.5C.
But the new report suggests the inclusion of recent evidence, reflected in the IPCC’s assessment, justifies a lower temperature range of 1.25C-3C, with a best estimate of 1.75C, for a doubling of CO2.
By contrast, the climate models used for projections in the assessment indicate a range of 2C-4.5C, with an average of 3.2C.
The report says new estimates point to climate sensitivity most likely being under 2C for long-term warming over 70 years.
“The observational evidence strongly suggest that climate models display too much sensitivity to carbon dioxide concentrations and in almost all cases exaggerate the likely path of global warming,” Mr Lewis said.