Saturday, April 14, 2012

I don't know and neither does anyone else!

Today, with a "High Risk" of a major tornado outbreak in the forecast, some recent experiences prompt me to discuss a tornado-related topic that seems to be springing up everywhere, sort of like playing a game of Whac a mole.  The question is ... wait for it ... Will global climate change cause an increase in the frequency and/or intensity of tornadoes?

I recently had an extended email discussion  on this topic with a famous climate scientist after I posted a blog on the subject.  That scientist, not a specialist in severe convective weather, seems reluctant to accept the arguments of a fellow scientist who has spent 40 years studying tornadoes and tornado climatology, or to do anything to correct "misstatements of his position" on the subject in the popular media.  Whatever - I have no means to control the words/actions of others, nor do I wish to have such control.

The more time I've spent looking at our data regarding the occurrence of tornadoes, the more concerned I've become about the relationship between those data and the unknown true time-space distribution of tornadoes in the USA.  I've said on many occasions that the USA has the best data regarding tornado occurrence in the world, but our data still pretty much suck!  They're dominated by the heavy hand of non-meteorological influences:  population density, challenges to rating tornado intensity, reporting practices, politics of various sorts, and so on.  The effects of these "secular" factors only become evident as one works with the data.

It's indeed logically possible that some of the changes we see over time in the space-time distribution of tornado reports are the result of global climate change.  I certainly have no basis for ruling that out.  Unfortunately, I can't rule out the possibility that global climate change has, as yet, had no effect, either!  Given the very strong signal of a increasing tornado frequency, it seems inevitable that people examining the data for the first time would be impressed most by that very obvious trend in the data. Even a relatively sophisticated newcomer capable of using tools like statistical analysis on the data couldn't avoid being dominated by that trend.   The problem is that deeper examination of the data eventually reveals large biases that clearly have nothing to do with meteorology.

Our tornado data simply do not permit the drawing of conclusions with high confidence about possible changes in the space-time distributions of tornadoes.  No simple adjustments of the data - say, accounting for population bias - can remove the multitude of secular changes that resist being characterized easily in time and space.  Population bias is only one amongst the multitude and it's relatively easy to accommodate, whereas many of the other factors are much more difficult to account for, or even to characterize.  Given the potential significance of the effects arising from anthropogenic global warming, it's easy to understand why someone would jump on a superficial analysis of the tornado occurrence data to make unjustifiable, speculative statements about the future for tornadoes.  But the simple fact is I don't know what's going to happen and neither does anyone else!  Anyone who asserts that they do know what's going to happen with respect to future tornado occurrences has no scientific foundation upon which to stand. 

I'm not happy about this situation, but scientific integrity demands that I acknowledge it and behave accordingly.  I see little or no potential for the development of an extensive data base about tornadoes free of these secular influences any time in the next several decades.  I know of no way to obtain highly accurate data that would reveal the true space-time distribution of tornadoes.  Even if some such solution did exist, we would have to use it for many decades to develop a sufficient sample of events to justify making confident statements about temporal changes in the space-time tornado distribution.

Therefore, this problem isn't going away any time soon, barring some sort of unforeseen new developments in the climatological analysis of tornado occurrence data.  Absent highly reliable information about that true distribution, any hypothesis based on the historical record of tornadoes regarding the future of tornado occurrences as the global climate changes is going to remain speculative - which is to say, outside of the domain of good science.


Roger Edwards said...

Thanks for posting that, Chuck. May I guess your discussion with Kevin Trenberth wasn't very productive, at least in this sense?

I've examined historic tornado data not as much as you, but a lot nonetheless, over the past 25 years. I agree fully with your statements here.

I've reviewed multiple papers claiming, in effect, that "global warming" is boosting their chosen measure of tornadoes (i.e., all-CONUS, all in the Southeast, TC tornadoes in Florida, CONS strong/violent).

Every one of them was profusely riddled with speculative, hand-waving rubbish. Each one reeked with the classic causation/correlation fallacy. One manufactured an F3-F5 tornado trend out of thin air that doesn't exist (essentially, those have flatlined for decades, to the extent we can tell). None were authored by scientists we know to be familiar with the problems of the tornado data, nor did they reference key papers you and others have authored that discussed such.

One particularly egregious formal submission did little more than the following:

1. See Mann's "hockey stick";
2. See the increase in Atlantic TCs over the past several years, including category 4-5 storms (paper was circa 2007, right after the big 2004-5 AMO-associated spikes in TC occurrence...naturally!);
3. See all these major hurricanes over and near Florida in the last few years;
4. See the increase in TC tornadoes over FL;
5. Global warming is causing TC tornadoes to increase in number and intensity over FL.

Fortunately, this paper was rejected unanimously. Disturbingly, it was lead-authored by a major university professor of atmospheric-science(co-authored by a student), who most certainly should have known better than to submit that garbage.

As you know, some folks in climate science are going straight to the media with absolutely unsubstantiated claims on AGW and tornadoes. Clearly there's a voracious desire in some quarters to hitch tornadoes to the AGW wagon. Do you have any ideas why?

I also don't see why is is so stinking difficult for not only the media, but *fellow scientists*, to accept the notion that there isn't enough evidence to say. What's the problem with admitting the simple truth--that we just don't know?

Chuck Doswell said...

My email interaction with Kevin indeed proved to be unsatisfying. I'm not sure why some climate scientists choose to use the media the way they do, but I presume their intention is to inform the public of the situation - as they see it. This isn't inherently a bad thing, but my experiences with the media suggest that it's almost always a waste of time. Even in the odd case where what you say isn't distorted, misquoted, or taken out of context - it will be drowned in a tsunami of nonsense from the media. Your one shining instance of meaningful reportage will be buried in an avalanche of crap. This is why I no longer do media interviews.

Mario Lopez said...

Linking a couple highly active tornado seasons to climate change is indeed a disturbing suggestion by a few climate scientists, although I may add that no climate scientist I know would do that. Almost all climate scientists should be aware that tornado formation is much more closely linked to the highly detailed dynamics of individual storms than to global average surface temperatures.

The most dangerous thing is that the next time we experience a relatively inactive tornado season (which is sure to happen at some point in the future) the general public will see it as an indication that global warming isn't real. I feel that the public lost interest (or lost "belief") in global climate change after the 2005 hurricane season ended, which many people tried to use as evidence of global warming.