Friday, August 31, 2007

There are models and then there are models

Some NASA scientists recently published an article in Journal of Geophysical Research Letters which shows that severe thunderstorms may be more intense in a warmer world.

There's nothing wrong with the article or the science, but I have a quibble with the press release NASA put out about it. It seems to imply that NASA built an entirely new climate model. Consider the opening paragraph:
NASA scientists have developed a new climate model that indicates that the most violent severe storms and tornadoes may become more common as Earth’s climate warms.

Wow! A whole new climate model? NASA sure has been busy! There's more:
Previous climate model studies have shown that heavy rainstorms will be more common in a warmer climate, but few global models have attempted to simulate the strength of updrafts in these storms. The model developed at NASA’s Goddard Institute for Space Studies by researchers Tony Del Genio, Mao-Sung Yao, and Jeff Jonas is the first to successfully simulate the observed difference in strength between land and ocean storms and is the first to estimate how the strength will change in a warming climate, including “severe thunderstorms” that also occur with significant wind shear and produce damaging winds at the ground.

I know how hard it is to make a climate model so I didn't think it was really a new model. Indeed the article said that Dr. Genio et al. had simply altered one small part, the convection parameterization, of the NASA GISS Model E which is probably 3-4 years old. Its more accurate to say that Dr. Genio et al. have developed a new model of convection and placed this in the larger model of the global atmosphere. Those two uses of the word "model" are very different. I would expect this distinction to be lost somewhere but not in the NASA press release.

The press release, or slightly re-written versions of it, have shown up in a couple of places so far: ScienceDaily and even Fox News.


Kit Stolz said...

Interesting...I see that Stanley Changnon has a paper out in Climate Change on catastrophic winter losses. Not the same thing, but maybe a related phenomenon?

Unfortunately, I'm just not willing to pay $32 to read a single article, so it's difficult for me to get a sense for it. But I'd be curious to hear if you think it's worth reporting on.

Rob said...

Hello Kit,

I tracked down the article and agree that its related. Mr. Changnon looks at historical data instead of doing a model run like the NASA folks. His classification shows that storm number has decreased over 1949-2003, but intensity, and thus damage, has increased. His last paragraph says "These findings agree with expectations of winter storm conditions under global warming" and cites the 2001 National Assessment.

Now we need someone to finish the story: look at winter storms in 21st century predictions and summer storms in 20th century data.

Kit Stolz said...

Thanks for looking that up, and for thinking it through. Very helpful.