15-year warming pause is ‘settled’

THE existence of a more than 15-year “pause” in average global surface temperatures has been “settled” but scientists remain split on what it means.

THE existence of a more than 15-year “pause” in average global surface temperatures has been “settled” but scientists remain split on what it means for the future.

While the level of carbon dioxide in the atmosphere has continued to rise, global surface temperatures have not increased at the same pace, causing speculation over what has happened to the “missing heat”.

Some leading climate scientists claim the missing heat has been absorbed by the world’s oceans and will return with rapid future warming. But new research has found the Earth’s climate is much less sensitive to carbon dioxide than previously thought.

Michael Asten from Monash University’s School of Earth ­Atmosphere and Environment said that, while opinions on causes differed, the existence of the pause was settled.

“Only activists dare claim the pause in global temperature does not exist,” Professor Asten said.

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Australia’s leading public science organisation, CSIRO, has ­acknowledged the “hiatus” but says its existence does not detract from the urgency of addressing human carbon dioxide emissions.

CSIRO Oceans and Atmosphere Flagship director Helen ­Cleugh said measurements did show that the rate at which global mean surface temperature had warmed in the past decade was less than in the previous decade. But she said actual temperatures had remained at historic highs. She said that when the entire climate system was considered, the Earth had continued to warm.

“Measurements across the oceans and Earth system as a whole show that warming has continued unabated throughout this period,” Dr Cleugh said.

Climate Council chief executive Amanda McKenzie said her organisation, which includes Will Steffen and Tim Flannery, did not accept there had been a pause.

“No, 2013 marked the 37th year in a row that the yearly global temperature was hotter than the average,” Ms McKenzie said.

“Vested interests have been using the so-called pause to spread doubt and misinformation.”

Federal Environment Minister Greg Hunt said warming of the climate system was “unequivocal”.

“The climate system, which includes the atmosphere, oceans, land and ice, has continued to accumulate heat over the last 18 years,” he said. “The government fully accepts the science.”

Most research has focused on finding the extra heat elsewhere in the climate system. NASA has ruled out an early theory that it was hiding in the deep oceans below 2000m. Other papers have claimed it could be located in the north Pacific and Atlantic oceans.

Another paper says warming of the Southern Ocean has been underestimated in the past.

Dr Asten said he believed the pause in surface temperatures would force scientists to re-examine fundamental assumptions in climate science. “The hiatus demonstrates a disconnect between climate models up to 2013 and physical measurements on our ‘laboratory Earth’,” he said.

Dr Asten said research was showing climate sensitivity was lower than thought.

A recent peer-reviewed paper by US-based climate scientist Judith Curry estimated the Earth’s climate had a much lower climate sensitivity to CO2 than predicted by the IPCC reports. As a result, Dr Curry said there were serious questions about whether the climate model projections of 21st-century temperatures were fit for making public policy decisions.