The most accurate climate change models predict the most alarming consequences, study finds

The most accurate climate change models predict the most alarming consequences, study finds
By Chris Mooney
Dec is 6 2017
https://www.washingtonpost.com/news/energy-environment/wp/2017/12/06/the-most-accurate-climate-change-models-predict-the-most-alarming-consequences-study-claims/

The climate change simulations that best capture current planetary conditions are also the ones that predict the most dire levels of human-driven warming, according to a statistical study released in the journal Nature Wednesday.

The study, by Patrick Brown and Ken Caldeira of the Carnegie Institution for Science in Stanford, Calif., examined the high-powered climate change simulations, or “models,” that researchers use to project the future of the planet based on the physical equations that govern the behavior of the atmosphere and oceans.

The researchers then looked at what the models that best captured current conditions high in the atmosphere predicted was coming. Those models generally predicted a higher level of warming than models that did not capture these conditions as well.

The study adds to a growing body of bad news about how human activity is changing the planet’s climate and how dire those changes will be. But according to several outside scientists consulted by The Washington Post, while the research is well-executed and intriguing, it’s also not yet definitive.

Government’s dire climate change report blames humans

The government’s National Climate Assessment cited human influence as the “dominant cause of the observed warming since the mid-20th century.” (Patrick Martin/The Washington Post)

“The study is interesting and concerning, but the details need more investigation,” said Ben Sanderson, a climate expert at the National Center for Atmospheric Research in Boulder, Colo.

Brown and Caldeira are far from the first to study such models in a large group, but they did so with a twist.

In the past, it has been common to combine together the results of dozens of these models, and so give a range for how much the planet might warm for a given level of carbon dioxide emitted into the atmosphere. That’s the practice of the leading international climate science body, the United Nations’ Intergovernmental Panel on Climate Change.

Instead, Brown and Caldeira compared these models’ performance with recent satellite observations of the actual atmosphere and, in particular, of the balance of incoming and outgoing radiation that ultimately determines the Earth’s temperature. Then, they tried to determine which models performed better.

“We know enough about the climate system that it doesn’t necessarily make sense to throw all the models in a pool and say, we’re blind to which models might be good and which might be bad,” said Brown, a postdoc at the Carnegie Institution.

The research found the models that do the best job capturing the Earth’s actual “energy imbalance,” as the authors put it, are also the ones that simulate more warming in the planet’s future.

Under a high warming scenario in which large emissions continue throughout the century, the models as a whole give a mean warming of 4.3 degrees Celsius (or 7.74 degrees Fahrenheit), plus or minus 0.7 degrees Celsius, for the period between 2081 and 2100, the study noted. But the best models, according to this test, gave an answer of 4.8 degrees Celsius (8.64 degrees Fahrenheit), plus or minus 0.4 degrees Celsius.

Overall, the change amounted to bumping up the projected warming by about 15 percent. The researchers presented this figure to capture the findings:

[snip]

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