A study suggesting that the “pause” in global warming is not real has managed to unify climate scientists and their arch-sceptics over the need for further research to clarify whether global average temperatures really have flat-lined over the past 15 years.
Rasmus Benestad of the Norwegian Meteorological Institute in Oslo, who was one of the first scientists to try to estimate the effect of the missing Arctic warming data on global average temperatures, said that the latest study is a useful contribution to the debate.
“The pronounced recent warming can be inferred from different and independent observations, such as the melting of the ice on Greenland, thawing of permafrost, and the reduction of the sea-ice. Hence, when the most rapidly warming regions on Earth are not part of the statistics, the global mean estimate is bound to be lower than the real global mean. Hence, our picture of Earth’s surface temperature is somewhat ‘patchy’,” Dr Benestad said.
It is likely that the slowdown in global average temperatures to the Earth’s surface is the result of a combination of factors, such as the uptake of heat in the deep oceans, the effect of El Nino and La Nina conditions in the Pacific Ocean, in addition to the hidden temperature increases in the Arctic, he said.
Professor Richard Allan of the University of Reading said that the study by Cowtan and Way appears reasonable as they have tested their method by applying the technique to regions of the world where there are ground-based measurements to gauge its accuracy. However, the study is still preliminary and will need to be scrutinised by other scientists, Professor Allan said.
“There is still a slowdown in the rate of global average surface warming in the 21st century compared to the late 20th century and this still looks to be caused by natural fluctuations in the ocean and other natural climate fluctuations relating to volcanic eruptions and changes in the brightness of the sun,” Professor Allan said.
“However, the size of this slowdown and the discrepancy between observations and climate simulations may be less than previously thought. The conclusions of the IPCC stands: we can expect a return to substantial warming of the planet over the coming decades in response to rising concentrations of greenhouse gases,” he said.
Ed Hawkins of Reading University added: “This is an interesting and important contribution to the continuing discussion about the recent temperature hiatus, but is unlikely to be the final word on the issue. It must also be remembered that a 15-year trend is still too short to be considered as representative of longer-term global temperature trends, and also too short to be meaningfully compared with climate simulations.”
The Conservative MP Peter Lilley said that he is not convinced that the latest study can explain the pause. “The IPCC tried to explain the pause by saying the heat is in the deep ocean and now these people say it’s in the polar regions. They both can’t be right,” Mr Lilley said.