James Ihaka

James Ihaka is a Herald reporter based in Hamilton.

Lid lowered on global warming rate

Research finds top end of estimates too high but still above agreed 2C target.

Global warming is shrinking the environments of polar bears and threatening low-lying island nations. Photo / Supplied
Global warming is shrinking the environments of polar bears and threatening low-lying island nations. Photo / Supplied

New research from Oxford University shows the rate of global warming has been lower over the past decade than it was previously.

The paper, "Energy budget constraints on climate response", to be published online by Nature Geoscience, shows the estimated average climate sensitivity - or how much the globe will warm if carbon dioxide concentrations are doubled - is almost the same as the estimates based on data up to the year 2000.

The two estimates of the average are only 0.1C different.

The study, which uses data from the past decade, also shows the most extreme rates of warming simulated by climate models over 50- to 100-year timescales are looking less likely.

The findings used the most up-to-date information on temperatures, energy flows and energy accumulation in the climate system available to the next Scientific Assessment of the Intergovernmental Panel on Climate Change, which is due to be finalised in September.

Victoria University climate scientist James Renwick said there was always a range of uncertainty and it had been hard to rule out the possibility that the climate sensitivity might be very large.

"Using the latest data shows that those very high sensitivities look much less likely, so we've been able to tighten the range of uncertainty, especially at the high end," he said.

"We have much more comprehensive and reliable data on ocean heat content these days, and there haven't been many large volcanic eruptions lately to obscure things, so that has allowed a better estimate of the range of climate sensitivity."

Dr Alexander Otto, from Oxford University, said recent observations suggested the expected rate of warming in response to rising greenhouse gas levels was likely to lie within the range of current climate models but not at the high end.

Professor Reto Knutti of ETH Zurich said even at the low end of the range warming would be well over the two-degree goal that countries had agreed to.

- NZ Herald

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