Climate Scientists Encounter Limits of Computer Models, Bedeviling Policy



At least 20 older climate models disagreed with the new one at NCAR, an open-source model called the Community Earth System Model 2, or CESM2, funded mainly by the U.S. National Science Foundation and arguably the world’s most influential. Then, one by one, a dozen climate-modeling groups around the world produced similar forecasts.

The scientists soon concluded their new calculations had been thrown off kilter by the physics of clouds in a warming world, which may amplify or damp climate change. “The old way is just wrong, we know that,” said Andrew Gettelman, a physicist at NCAR who specializes in clouds and helped develop the CESM2 model. “I think our higher sensitivity is wrong too. It’s probably a consequence of other things we did by making clouds better and more realistic. You solve one problem and create another.”

Since then the CESM2 scientists have been reworking their algorithms using a deluge of new information about the effects of rising temperatures to better understand the physics at work. They have abandoned their most extreme calculations of climate sensitivity, but their more recent projections of future global warming are still dire — and still in flux.


Skeptics have scoffed at climate models for decades, saying they overstate hazards. But a growing body of research shows many climate models have been uncannily accurate. For one recent study, scientists at NASA, the Breakthrough Institute in Berkeley, Calif., and the Massachusetts Institute of Technology evaluated 17 models used between 1970 and 2007 and found most predicted climate shifts were “indistinguishable from what actually occurred.”

Still, models remain prone to technical glitches and are hampered by an incomplete understanding of the variables that control how our planet responds to heat-trapping gases.

Author(s): Robert Lee Hotz

Publication Date: 6 Feb 2022

Publication Site: WSJ