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Rebels Turn On IPCC Over Climate Sensitivity

Graham Lloyd, The Australian

It is clear that some IPCC scientists think the projected rise in CO2 levels might not have such a big warming effect as was once thought.

AS the world’s climate scientists prepare to deliver their much-awaited updated Intergovernmental Panel on Climate Change report on climate change next month, they face an unwelcome barrage of former friendly fire posing a fundamental and uncomfortable question — did they get it wrong on what increased CO2 emissions mean for global temperatures?

Complaints have been made about a noticeable change in attitude by news organisations to climate change reporting, including Germany’s Der Spiegel, the New York Times, which closed its environment bureau, and Reuters news agency.

The Economist magazine has infuriated many with a report questioning climate sensitivity, the measure used by researchers for how much they expect temperatures to increase in response to particular increases in levels of carbon dioxide in the atmosphere.

There were several caveats in The Economist article, based on a leaked table from a draft report of the upcoming IPCC text.

The table was put together by the IPCC working group on mitigating climate change, rather than the group looking at the physical science. It derives from a relatively simple model. Its publication illustrates an increasingly questioning mainstream media.

The Economist broke ranks with a report earlier this year that explored the now accepted view that average global temperatures had remained relatively steady for more than a decade despite a sharp rise in carbon dioxide levels.

After years of denial by the climate change community, even Australia’s Climate Commission in its recent Critical Decade update acknowledged a “plateau” in the global temperature rise between 1979 and 2012 was “clearly visible” in the temperature record.

The Climate Commission, like IPCC chairman Rajendra Pachauri, said the average surface temperature standstill could be explained by natural variations.

There is also robust debate about the extent to which the deep oceans are taking up the additional heat and the role played by particulate emissions from volcanos and more coal burning.

But for many people, the lingering question remains: is the earth’s climate less sensitive to carbon dioxide than originally thought.

According to the Economist, the table, not yet published by the IPCC, shows that at CO2 concentrations of between 425 parts per million and 485ppm, temperatures in 2100 would be 1.3C to 1.7C above their pre-industrial levels.

from The Economist, 20 July 2013

“That seems lower than the IPCC’s previous assessment made in 2007,” The Economist said. “Then, it thought concentrations of 445 to 490 ppm were likely to result in a rise in temperature of 2 to 2.4 degrees C.”

The Economist acknowledges the two findings were not strictly comparable. The 2007 report talks about equilibrium temperatures in the long term (over centuries); the forthcoming one talks about them in 2100. “But the practical distinction wound not be great so long as concentrations of CO2 and other greenhouse gas emissions were stable or falling by 2100,” The Economist said.

“It is clear some IPCC scientists think the projected rise in CO2 levels might not have such a big warming effect as was once thought.”

Detractors say The Economist has gone too far. An IPCC statement in response to the article said the draft seen by The Economist was a “work in progress”.

“The text is likely to change in response to comments from government and expert reviewers,” the IPCC said. “It is therefore premature and can be misleading to attempt to draw conclusions. Draft reports are intermediate products and do not represent the scientific view that the IPCC provides on the state of knowledge of climate change and its potential environmental and socio-economic impacts at the conclusion of the process.”

The Australian, 3 August 2013