The junior senator from Illinois recently gave a long speech on global warming, which included the following:
And while the situation on the land may look ugly, what's going on in the oceans is even worse. Hurricanes and typhoons thrive in warm water, and as the temperature has risen, so has the intensity of these storms. In the last thirty-five years, the percentage of Category 4 and 5 hurricanes has doubled, and the wind speed and duration of these storms has jumped 50%. A hurricane showed up in the South Atlantic recently when scientists said it could never happen. Last year, Japan set a new record when it suffered its tenth typhoon and the United States set a record for the most tornadoes we've ever had. And at one point, Hurricane Wilma was the most powerful storm ever measured.
On the one hand, I have to praise Obama and his staff--this passage suggests they conducted some individual research. However, two errors: 1) Hurricane Wilma was the most powerful storm ever measured in the Atlantic, not anywhere on the globe. And more importantly 2): I know of no basis for talking about tornadoes in the context of global warming. I'm not aware of any theory on why they should increase in strength, much less any data backing that theory up. So unfortunately, I have to conclude that Obama has gone too far in this instance.
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And it's posts like this that distinguish members of the reality-based community from the nutjobs ranged against them. Kudos.
I was curious about your statement that there's no link between GW and tornadoes - I thought I'd heard that there may be some sort of link (though not as clear as that between GW and hurricanes). So I scanned Google Scholar and found a couple references - sounds like the jury's still out on this one:
Epstein, P.R. 2000. Is Global Warming Harmful to Health? Scientific American (volume #?):50-57.
- argues that warming of land areas leads to increased parching, which increases pressure gradients and leads to stronger storms, including tornadoes (p. 52)
Dale et al. 2001. Climate change and forest disturbance. BioScience 51:723-734.
- "Small-scale wind events are products of mesoscale climatic circumstances and thus may be affected by climate changes, although the type and amount of alteration in windstorm characteristics cannot be predicted because these smaller-scale events are below the resolution of today's GCMs"
- Also cites a number of other references (Berz 1993, Karl et al. 1955a & b), and Etkin 1995 supporting an increasing trend in extreme thunderstorm & tornado events, a link between tornadoes and mean temperature, and a hypothesis by Berz that "increased intensity of all atmospheric convective processes will accelerate the frequency and intensity of tornadoes and hailstorms".
Houghton, J. 2005. Global Warming. Rep. Prog. Phys. 68:1343-1403.
- argues that there's currently insufficient information to globally model small-scale events e.g., tornadoes (p. 1380)
What's your take on this work? I haven't followed it too closely, so I don't know what support exists for these studies.
Good luck with your revisions - and keep up the great work, I'm glad somebody's following these issues and keeping them in the headlines!
N
nolagal--
Wow, okay, guess I have to backtrack a bit--there clearly is some literature out there, though it does seem largely speculative as to what GW might do....I should also have noted that hurricanes often spin off tornadoes, and thus if GW changes hurricanes in some way, there is a potential effect on tornadoes as well (though I can't imagine what)....
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Climate change is a difficult issue. Public speech about it is bound to contain errata (like the one you point out about Hurricane Wilma). It's good to correct them, but it's something else entirely to say the speech shouldn't have been made. I would praise Obama and his staff for not only doing the research, but tackling the issue in the first place.
The tornado connection is incredibly tenuous at best. The report databases are insufficiently accurate or consistently recorded to detect anything, even in the US where the database is the best in the world. There's no evidence of an increasing number of tornado events in the US over the years. Reports have increased, but the reporting databases have changed enough that they're unusable. There's no reason to believe the western Canadian data are good enough to make any connection.
The relationship between temperature and tornado occurrence is pretty weak and nonlinear. Yes, there are more tornadoes in the warm season than in winter, but in most of North America, there are more tornadoes in the spring/fall than in the dead of summer.
Stronger convection, if that occurs, will not necessarily lead to more tornadoes. Our best hope in detecting changes will be in looking at changes in frequency of the environmental conditions in which tornadoes form, not the storms themselves. I've outlined some preliminary work on it at http://www.nssl.noaa.gov/users/brooks/public_html/papers/AMS2K6.pdf. The balance between the various ingredients is such that we can have little confidence in forecasts of change at this time. Since writing that, I believe I've detected a slight increase in the favorable environments for severe thunderstorms since the mid-1970s in the NCAR/NCEP reanalysis data for the US, but only back up to the levels since in the late 1950s. In South America, the numbers have decreased ~30% since the 1950s. For tornadoes, trends are in the noise, not even taking into account the lower quality of the relationship between the environments and the events, compared to non-tornadic severe thunderstorms.
I hadn't heard the "land parching" theory before. That makes little physical sense to me.
Hurricane-spawned tornadoes are a fairly small component of the tornado events in the US and confined to a relatively small class of hurricanes (typically making landfall moving to the north). They make up a few % of the US events. There's no obvious connection to intensity of the tropical storm. I doubt if we'd be able to detect any changes.
I could argue for increases or decreased in tornado events based on fairly basic principles. Attempting to adjust for report changes over the years, in the last 5 years, we've seen one of the biggest tornado years on record (2004) and one of the smallest (2002).
Thanks Harold. I'd say that about covers it. So, to Barak Obama: You're great, but you gotta fact check....
My personal WAG is that he simply misspoke and meant to say the US had the most hurricanes ever.
I do believe Coby is right. Even if the tornado reference was correct, it doesn't really belong in that sentence or that paragraph. Also, bear in mind that this is the time of year when tornados are high in the consciousness of people in Tornado Alley (as Chicago is), so it may just have been an unconscious slip. Also, given how these kinds of speeches actually get produced, my suspicion is that the the Wilma Atlantic reference was there in an earlier draft but got excised by a speech writer who wasn't personally familiar with the material.
Reading over the whole speech, what I was most troubled by was the emphasis on solving the problem by way of large subsidies to the fossil fuel and auto industries. It's telling that Obama didn't see the contradiction between this and the immediately preceding commitment to market solutions (which was weak enough because the only approach he mentioned was the abuse-prone cap-and-trade scheme). So while on the one hand it's clear that we will get some kind of action on GW from the Democrats once they get back in power, that action is very likely to be both expensive and of questionable effectiveness.
The weather may be getting worse, but the viewing is getting better.
http://www.spc.noaa.gov/coolimg/