Error Correction Means California’s Future Wetter Winters May Never Come
Brendan Bane, Pacific Northwest National Laboratory, via Phys.org | December 15, 2020

California and other areas of the U.S. Southwest may see less future winter precipitation than previously projected by climate models.

After probing a persistent error in widely used models, researchers at the Department of Energy’s Pacific Northwest National Laboratory estimate that California will likely experience drier winters in the future than projected by some climate models, meaning residents may see less spring runoff, higher spring temperatures, and an increased risk of wildfire in coming years.

Earth scientist Lu Dong, who led the study alongside atmospheric scientist Ruby Leung, presented her findings at the American Geophysical Union’s fall meeting on Tuesday, Dec. 1, and will answer questions virtually on Wednesday, Dec. 16.

As imperfect simulations of vastly complex systems, today’s climate models have biases and errors. When new model generations are refined and grow increasingly accurate, some biases are reduced while others linger. One such long-lived bias in many models is the misrepresentation of an important circulation feature called the intertropical convergence zone, commonly known as the ITCZ.

Do these imperfect simulations with biases and errors generate, let’s say, predictions of whopping 2-degree changes over the next hundred years, as we’ve heard ad infinitum?

And what exactly have been the margins of error reported for these imperfect simulations with biases and errors upon which national policies have been predicated? Or for this new study, for that matter?

Doubling down on climate model bias

Heh. That’s your subtitle, not mine.

Many climate models mistakenly depict a double ITCZ: two bands appearing in both hemispheres instead of one, which imbues uncertainty in model projections. Scientists refer to this as the double-ITCZ bias.

Variations in the wind and pressure systems that influence the ITCZ add to that uncertainty.

“There’s a lot of uncertainty in California’s future precipitation,” said Dong, who described climate models that project a range of winter wetness in the state averaged over multiple years, from high increases to small decreases. “We want to know where this uncertainty comes from so we can better project future changes in precipitation.”

It comes from those who write the grants.