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Climate Models Backed

Comparing climate model projections directly with observed global warming trends is like “comparing apples with oranges”, according to research published in Nature Climate Change.

The analogy comes after some studies questioned whether climate model projections were overestimating recent temperature trends given a slowdown in the rate of surface warming over the past 15 years. However, Prof Stephan Lewandowsky of The University of Western Australia argues that the models have predicted global warming trends well when other key influences are taken into account.

“One of the most important drivers of internal variability is the El Niño–La Niña oscillation, which determines how much heat is taken up by the oceans rather than the atmosphere,” Lewandowsky said.

When he and his co-authors focused on models that were synchronised with the El Niño–La Niña phase of the oceans, they found that the models were accurately estimating recent temperature trends and were even mirroring the spatial distribution of heat in the oceans.

“The results show that models selected in this way provide good estimates of 15-year trends over the past half century, including for the most recent 15-year period,” said co-author Dr James Risbey of CSIRO Oceans and Atmosphere.

Risbey said that 15-year temperature trends sped up and slowed down in response to natural climate variations represented by El Niño- or La Niña-dominated periods.

“The preference for El Niño or La Niña periods in the climate model projections is not synchronised between models and the real world,” he said. “This means that any particular model is not expected to give the same 15-year trend as observations in any given 15-year period.

“Thus, comparing model projections directly with observed trends is comparing ‘apples with oranges’.”