Climate models

Climate models disagree on reasons for temperature ‘wobbles’

A new study led by Duke University finds that most climate models likely underestimate the degree of decade-to-decade variability in mean surface temperatures as Earth’s atmosphere warms. The models also provide inconsistent explanations for why this variability occurs in the first place.

These discrepancies can undermine the reliability of models for projecting the short-term rate as well as the magnitude of future warming, the study authors warn. As such, we should not overinterpret recent temperature trends.

“The inconsistencies we found among the models are a reality check that we may not know as much as we thought,” said lead author Patrick T. Brown, Ph.D. . climatology student at Duke’s Nicholas School of the Environment.

“That doesn’t mean that greenhouse gases aren’t causing Earth’s atmosphere to warm in the long term,” Brown pointed out. “It just means that the road to a warmer world may be bumpier and less predictable, with more temperature swings from decade to decade than expected. If you’re worried about climate change in 2100, don’t overinterpret short-term trends. . Don’t assume that the reduction in the rate of global warming over the past 10 years predicts what the climate will be like 50 or 100 years from now.”

Brown and his colleagues published their findings this month in the peer-reviewed journal Geophysical Research Journal.

To conduct their study, they analyzed 34 climate models used by the Intergovernmental Panel on Climate Change (IPCC) in its fifth and final assessment report, finalized last November.

The analysis found good consistency among the 34 models explaining the causes of year-to-year temperature variations, Brown noted. The inconsistencies existed only in terms of the model’s ability to explain decade-to-decade variability, such as why global average surface temperatures warmed rapidly during the 1980s and 1990s, but remained relatively stable since then.

“When you look at the 34 models used in the IPCC report, many give different answers about what causes this variability from decade to decade,” he said. “Some models point to the Pacific Decadal Oscillation as the cause. Other models point to other causes. It’s hard to know which is good and which is bad.”

Hopefully, as the models get more sophisticated, they’ll coalesce around a single answer, Brown said.

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