Climate Change Ups Odds Of Heat Waves, Drought

Reporting in the Bulletin of the American Meteorological Society, researchers write that extreme heat waves, such as the one last year in Texas, are 20 times more likely today than they were in the 1960s. NOAA climatologist Tom Peterson discusses what future climate change may bring.

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This is SCIENCE FRIDAY; I'm Ira Flatow. It seems like every time there's freak weather - a giant snowstorm, a heat wave, Hurricane Irene - everyone wonders: Did this happen because of climate change? And the answer from experts is usually, well, we can't say climate change caused this particular event.

But this week, scientists published a series of studies that makes the connection between climate change and extreme weather a bit clearer, connecting the dots so precisely in some cases that they could put a number on it.

Take last summer's heat wave in Texas. Looking at that data, scientists concluded that heat waves like that one are 20 times more likely to happen today compared to in the 1960s. And what's changed between then and now? The climate. So they say our warming world may be increasing the odds of more severe weather.

Is it too soon to connect the weather with the climate? Think you've seen the effects of climate change where you live? Give us a call. Our number, 1-800-989-8255. You could also tweet us @scifri, @-S-C-I-F-R-I, or go to our website at Tom Peterson is principal scientist at NOAA's National Climatic Data Center in Asheville, North Carolina. He joins us. Welcome to SCIENCE FRIDAY, Dr. Peterson.

TOM PETERSON: Thank you.

FLATOW: Tell us about this packet of studies. A few of them do connect climate change to some odd weather. Give us, for example, the one about Texas, the heat wave.

PETERSON: Well, thank you. So yes, our paper is trying to bring together a lot of quick analyses of the previous year and try to help foster the growth of the science. So the analysis of Texas was done by a group from both Oregon University or rather Oregon State University and some colleagues in the U.K.

And their analysis, in order to look at the tails of the distribution, when you try to do analyzings with climate models, in order to look at the tails of the distribution, you know, far out, the rare events, you need a lot of iterations of the models. And this was really kind of an interesting task because in order to run the climate models enough, it was sort of - it became a citizen science project, where people donated their home PCs to run the climate model at night when they weren't using them.

And so with that result, they had lots of iteration using the existing sea surface temperature and atmospheric composition during the 1960s and then again later during the 2000s. And they were able to compare the El Nino years in the 1960s with the 2008 El Nino as a surrogate for the 2011 El Nino. And from looking at that, what they've discovered is that the probability of this magnitude of a heat wave and a drought associated with La Nina has become 20 times more likely under current climate conditions than they were back in the 1960s.

FLATOW: Are there cases where the dots could not be connected in the study?

PETERSON: Yes, one of the more interesting studies is on the flooding in Thailand. As you may remember from last year, it was a devastating flood that lasted a very long time in Bangkok, and the analysis of the precipitation in the basin that feeds the river down through Bangkok found out that the rainfall was about a 140-year return period. So it was something that would happen about once every 140 years.

Yet the flooding was really massive, and part of the conclusion that they had when looking at climate models and being able to see how the climate models were projecting precipitation, that it was just a rare event, a moderately rare event, a 140-year return period, natural event, because the climate models were not predicting increases in precipitation due to climate change in there.

So the devastating floods were probably more related - the devastation was more related to how people are changing buildings and building, you know, in a flood plain and how the catchment basin has changed from forest to agricultural land and having more runoff, things like that.

So it was interesting that they could not find any discernible link to climate change.

FLATOW: And have you gotten flak from other climatologists about you actually making links now?

PETERSON: There's been a couple criticisms about some of the individual studies that are somewhat valid in that, you know, more in-depth analysis could have been done by running climate models that perhaps more accurately reflected the conditions of that region, and then doing this careful analysis and maybe in two or three years, presenting some material.

And two or three years, you know, people will not really remember these events, and so part of it is that, and another part of it is communicating precisely. And it's a difficult thing to do because the exact nature of the question that's being asked governs the results.

You know, are you asking about the temperature, how warm it got, or are you asking about the probability of warm temperatures reoccurring? And those can wind up having different answers, so you have to be very cautious about the communication.

And that's really some of the questions that have been raised by other scientists is exactly, you know, are we communicating this as precisely, accurately as we should be? And if you get really precisely accurate, sometimes people can't really understand you with all the different caveats.

For example, the drought and heat wave in Texas, you know, to be precisely accurate, it is - when it's associated with a La Nina event are now 20 times more likely, though they didn't look at all events or conditions during other times, other years.

FLATOW: One thing, now that we're into the hurricane season, people wonder - you hear a lot about hurricanes in relation to climate change, especially in the Gulf - hurricanes in the Gulf. Do the studies you're talking about say anything about those hurricanes?

PETERSON: Our studies did not look at those in particular, but that is a subject of a lot of ongoing research, and I'm really not an expert enough to talk about that in detail.

FLATOW: OK. Do you think that we're going to be seeing more scientists who might come out making...?

PETERSON: Yes, indeed, you know, we used to say you can't - you know, as you said in your introduction, you can't attribute any single event, but this is really where the science is moving is trying to understand how these events are occurring. And it makes a lot of sense for somebody - like if you're considering building a factory just out of the 100-year flood plain, and then you see that the land there gets flooded, you wonder is this a really rare event, is this a 200-year event?

And it helps to understand whether this was a very rare event or that these major flooding conditions are now more likely. You know, it may affect how you build - where you build your factory and things like that. So people are interested in this, and, you know, people's interest often drives the science, that scientists want to answer the questions that people are concerned with.

So one of the goals of our paper is to foster the growth of the science, that these paper, these analyses were done by many different teams around the world, and we're hoping next year to have an additional suite of analyses to present.

FLATOW: Going back to the heat wave in Texas and in that region, does the heat wave lead to the drought? Is that the progression that it goes to? Or is it vice-versa?

PETERSON: I think the short answer is yes. If - as when you have drought, you have less water able to be evaporated or evapotranspirated from plants, and so more of the energy goes into sensible heat of warming the soil. So droughts can cause heat waves. At the same time, a really intense heat wave can cause a drought, because it fosters so much more evapotranspiration and evaporation of the water off the soil.

FLATOW: So it's sort of counterintuitive sometimes.

PETERSON: Well, it - they're both factors that are involved. I mean, we have seen in the Midwest where this recent heat wave, you know, a lot of the farmers are seeing the detrimental effects right away. And it came not because precipitation was lacking for a couple weeks so much as that it was just really, really warm, and it was evaporating a lot of water.

FLATOW: Let me get a quick phone call in here, from Troy(ph) in Iowa City. Hi, Troy.

TROY: Yes, I have read recently that some scientists believe that tree rings that were grown and such and such prove that it's - the Earth is actually cooling. And the next question is: If your computer models is right, they should be able to predict the temperature of, we'll just say, Iowa City, Iowa, July 4th and July 25th for the next three years. And what if your computer model or their computer model is right? What is the rainfall in Iowa?

And doesn't that - and didn't Michael Mann refuse to give out his raw data to prove that he was right that global warming is happening?

FLATOW: Let me get some answers. Thanks, Troy. Tom?

PETERSON: My goodness, several different questions. So one was about the tree rings indicating cooling in recent years. There's been actually a major study about a year or two years ago where they looked at all the different biological indicators that people were tracking, you know, where the fish are being caught and where the fish are being located, the timing of bird migrations, the timing of plant flowering and stuff.

And they found that, if I recall correctly, 85 percent of them were indicating warming. So there are some places that are cooling, and there are some places that are reacting and some species of birds and mammals that are reacting differently.

But overall, we're seeing that it's not just an artifact of our data, that, you know, the birds are migrating earlier, fish species are moving farther - moving poleward, and it's really clear.

And the second question he had was about predicting the weather. Can we predict the weather two years from now, three years from now, accurately? And there's a limit of predictability in the weather because the question is you may be able to see that a storm is coming, but exactly when the storm is coming, you know, you may not be able to predict well, and that diminishes the farther out you're predicting it.

But when you're dealing with climate, what we know is that we can easily predict that this summer is going to be warmer than next winter. Winter is going to be colder. And the factors that make winter cold and summer warm are the same factors that govern the climate and the long-term evolution of the climate, the amount of sunshine that we get, the angle of the Earth, the atmospheric gases that we have and that can absorb radiation.

So the climate prediction is much more akin to understanding the change of seasonal cycles and the forces that are affecting that, because now we're seeing - for example, we're seeing spring coming earlier.

FLATOW: And your data used 2011 as a year for your predictions?

PETERSON: What our analysis presented was we looked at 2011, just extreme events of 2011. There's a companion piece on the state of the climate that was also produced by over 300 scientists from around the world, and they looked at just trying to analyze all the different components of the atmosphere that we can understand and the sea surface temperature and land temperature and everything.

And a major report was just put out of 2011, kind of keeping track, sort of like a scorekeeper, of how the climate is changing and how the factors that change climate are changing.

FLATOW: All right, Dr. Peterson, thank you for taking time to be with us today. Tom Peterson is principal scientist at NOAA's National Climatic Data Center in Asheville, North Carolina. And he joined us from North Carolina. We're going to take a quick break and switch gears and talk about - well, we're going to come back and talk about alien life here on Earth. So stay with us. We'll be right back after this break.


FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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