Monday, April 02, 2012

Selection Bias Goes Both Ways

For the same reason I am skeptical about people who look at heat waves and find evidence of climate change, I am skeptical about people (especially meteorologists) who look at them and find evidence of just weather. Selection bias goes both ways.

The Washington Post reports on an nonpeer-reviewed NOAA study that found that 'freak chance' was the major reason for last month's US heat wave:
...The National Oceanic and Atmospheric Administration analyzed the causes and chances of what it nicknamed “meteorological March madness.” Meteorologist Martin Hoerling said the main cause was a persistent warm wind sending toasty air north from the Gulf of Mexico. The study is not peer-reviewed and some outside scientists say it is short-sighted.

“Climate change was certainly a factor, but it was certainly a minor factor,” Hoerling said.

He said the bigger issue was wind patterns. Low pressure in the Pacific Northwest and high pressure in New England created a perfect funnel, like the gutter lane in a bowling alley, for warm air in the Gulf of Mexico to head north. That air is about 15 to 20 degrees warmer than the air in the Midwest. From time to time that air heads north, but what is unusual is that the wind pattern stayed that way for about two weeks.
Look, in addition to climate there is always still weather. How else would an extreme weather event manifest itself except if it was driven to wherever it took place by meteorological pressure forces?

So meteorologists, who are educated in the tools of meteorology, are (it seems to me) going to look at events and see all their contours and arrows and find an explanation in the language their tools provide them.

It was the same with the Russian heat wave, where some saw "blocking." Blocking isn't really an explanation, it's just a description in a certain language. Surely that wasn't the first time such blocking had ever occurred. So why did the temperature rise so high with this blocking and not previous blockings?

The meteorologist above says, of the US heat wave (as paraphrased by the reporter), 'from time to time that air heads north, but what is unusual is that the wind pattern stayed that way for about two weeks.'

Well, how unusual was it? Had it ever happened before? If so, had the temperature risen that high before? If not, why not? Because there is more energy in the atmosphere, because the Earth has an energy imbalance.


Roger Pielke, Jr. said...

Sometimes words get in the way. Marty is a "climatologist" though he has a PhD from a meteorology department and a job title of "meteorologist."

In fact, I can't identify a single paper of his that would fall under "meteorology":

The full NOAA report is better than the WP summary anyway:

Anonymous said...


Blocking may be attributable to Arctic Amplification (and sea ice loss), according to a few new studies. Masters has a post on this. Notice the links within.

-- grypo

Anonymous said...

Also consider that there is nothing biased (not in a political sense anyway) about Hoerling's analysis. It merely asks different questions than what fractional attribution studies (eg Ramsdorf) do. One is using a model to estimate how much of the temperature increase can be attributed to GHG (Hoerling).

Others (Ramsdorf, Stott, Trenberth) look at how often that this type of event can be expected in a warming world.

Otto 2012 says these types of analysis are not contradictory.

It follows logically that a model designed to look at temp differences would not include reasons for meteorological events like blocking, as described in the link I gave in my last comment.