Another Study Finds That Climate Models Are ‘Over-Sensitive’ To CO2 Increases

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Scientists have been lowering their estimates of how much warming would occur if carbon dioxide levels were increased as empirical estimates improved and the global warming pause continued.

A new report published in the journal Climate Dynamics corroborates previous studies showing that the climate will warm less from carbon dioxide emissions than claimed by the Intergovernmental Panel on Climate Change (IPCC). The report found that doubling carbon dioxide concentrations would only cause 1.64 degrees Celsius of warming in the long-run.

“Our results, which use data from this year’s IPCC fifth assessment report, are in line with those of several recent studies based on observed centennial warming and strongly suggest complex global climate models used for warming projections are oversensitive to carbon dioxide concentrations,” said the report’s co-author Nic Lewis, an independent climate scientist.

Lewis co-authored a report with science writer Marcel Crok earlier this year which found many climate models running hot and overestimating climate sensitivity by 40 to 50 percent. The paper also criticized the IPCC for trying to hide the climate’s weaker response to carbon dioxide in its 2013 report by not giving a central climate sensitivity estimate.

Climate sensitivity is a measure of how much warming will occur if atmospheric carbon dioxide concentrations are doubled. It’s an important tool for climate scientists to estimate the impacts increasing emissions will have on the climate — but only if its accurate. The paper shows that other factors besides carbon dioxide greatly influence the climate, like aerosols.

Climate scientist Judith Curry, who co-authored the paper, wrote that “the uncertainties in external forcing are substantial, particularly for aerosols.”

“Is this paper the last word on climate sensitivity estimates? No,” Curry added. “The uncertainty analysis in the Lewis and Curry paper relates only to the uncertainty in external forcing, surface temperature and ocean heat uptake. There remains considerable meta uncertainty in the determination of climate sensitivity, including how the problem is even framed.”

The IPCC’s major assessment from 2013 put climate sensitivity “likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence).” But the IPCC did not give a central climate sensitivity estimate, a break from how the group published estimates in previous reports.

Though, the IPCC did lower the lower-bound climate sensitivity estimate from 2 degrees Celsius to 1.5 degrees Celsius. This was seen as an admission that climate sensitivity is less than previously thought, but a political unwillingness to explicitly state that — especially since the United Nations is trying to broker a global climate treaty.

The UN made its latest push for a climate treaty this week by hosting a summit in New York City which sought to convince world leaders to come to an understanding about cutting greenhouse gas emissions.

President Obama spoke at the conference, urging world leaders to fight global warming while offering little in the way of details on how he was going to get the U.S. to cut its emissions even further — a key part of the White House strategy to spur international action.

But Obama’s words fell on deaf ears world leaders from major economies, including China and India, opted not to attend the summit this week. Instead, many world leaders are waiting for the climate conference in 2015 to renegotiate a treaty to replace the Kyoto Protocol.

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