Climate Scientists Encounter Limits of Computer Models, Bedeviling Policy

BOULDER, Colo.—For almost five years, an international consortium of scientists was chasing clouds, determined to solve a problem that bedeviled climate-change forecasts for a generation: How do these wisps of water vapor affect global warming?

They reworked 2.1 million lines of supercomputer code used to explore the future of climate change, adding more-intricate equations for clouds and hundreds of other improvements. They tested the equations, debugged them and tested again.

The scientists would find that even the best tools at hand can’t model climates with the sureness the world needs as rising temperatures impact almost every region.

When they ran the updated simulation in 2018, the conclusion jolted them: Earth’s atmosphere was much more sensitive to greenhouse gases than decades of previous models had predicted, and future temperatures could be much higher than feared—perhaps even beyond hope of practical remedy.

“We thought this was really strange,” said Gokhan Danabasoglu, chief scientist for the climate-model project at the Mesa Laboratory in Boulder at the National Center for Atmospheric Research, or NCAR. “If that number was correct, that was really bad news.”

At least 20 older, simpler global-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 climate program. Then, one by one, a dozen climate-modeling groups around the world produced similar forecasts. “It was not just us,” Dr. Danabasoglu said.

‘You solve one problem and create another,’ says Andrew Gettelman, right, at the NCAR Mesa Laboratory; left, NCAR’s Gokhan Danabasoglu.

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 climate-change 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.

As world leaders consider how to limit greenhouse gases, they depend heavily on what computer climate models predict. But as algorithms and the computer they run on become more powerful—able to crunch far more data and do better simulations—that very complexity has left climate scientists grappling with mismatches among competing computer models.

While vital to calculating ways to survive a warming world, climate models are hitting a wall. They are running up against the complexity of the physics involved; the limits of scientific computing; uncertainties around the nuances of climate behavior; and the challenge

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Chiefs playoff outlook: Computer models don’t favor KC

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Kansas City Chiefs quarterback Patrick Mahomes hangs his head during the second half of an NFL football game against the Buffalo Bills Sunday, Oct. 10, 2021, in Kansas City, Mo. (AP Photo/Ed Zurga)

AP

The Kansas City Chiefs are below .500 through the first seven games of the NFL season for the first time since 2015, when they had a 2-5 record.

There is a sliver of good news in that comparison: the Chiefs ended up making the playoffs and were in the hunt for the AFC West title late in that season.

Can this year’s Chiefs team, which has a 3-4 record, repeat the feat? The computer models aren’t so sure.

The New York Times’ playoff picture gives the Chiefs a 34% chance of making the playoffs and a 12% shot of winning the division. Eight AFC teams have a higher percentage of qualifying for the postseason.

FiveThirtyEight.com is a bit more bullish on the Chiefs, giving them a 43% chance of being in the postseason and a 15% chance of being AFC West champions. There are eight conference teams ahead of the Chiefs in postseason chances.

PlayoffStatus.com gives the Chiefs just a 25% chance of making the playoffs and has 10 AFC teams ahead of them. They have an 11% chance of winning the West.

While the numbers aren’t favorable, Chiefs quarterback Patrick Mahomes said he’s embracing the opportunity to turn things around.

“I’m excited for it,” Mahomes said on “The Rich Eisen Show”. “I think the guys in this locker room are excited for the challenge and hopefully when we look back on this .. adversity we have and we can show that that was the reason why we became the team that we wanted to become.”

There is plenty of time for the Chiefs to improve their playoff chances. They have 10 games remaining, but five of them are against teams leading their division: Packers, Cowboys, Bengals and Raiders (twice).

In fact, no team faces a tougher slate of games to finish the season than the Chiefs, as James Palmer of the NFL Network noted.

Tankathon has those same numbers, and it’s worth noting the Raiders, who lead the AFC West, have the 16th most difficult remaining schedule (opponents have a combined .500 record). The remaining schedule for the Chargers, who have a 4-2 record, is ranked 27th (.440 opponent records).

Two other teams of note: the Bills’ schedule is ranked 30th (.403) and the Titans’ is 32nd (.379).

This story was originally published October 28, 2021 10:53 AM.

From covering the World Series to the World Cup, Pete has done a little bit of everything since joining The Star in 1997.


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