Can Climate Change Explain Odd Weather?

From a deep freeze in California to ice storms and frigid temperatures across much of the United States, winter is finally here. Kevin Trenberth, senior scientist at the National Center for Atmospheric Research, talks about extremes in recent weather.

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IRA FLATOW, host:

You're listening to TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow. We're slated to talk about the weather this hour for the rest of this segment. Winter has finally arrived in the East Coast. If you want to talk about the weather, our number is 1-800-989-8255, 1-800-989-8255, 1-800-989-TALK. Getting ready to talk about the weather, it is - we did, as I say, back east we got our first taste of snow this - last night. Just a little bit, but this has been a lot of snow for us this year because we've had weather - we've set records. We had a day in New York where a few weeks ago it was 71 degrees. We've had broken weather, heat records that go back over 100 years.

And we know out west you're having this same sort of weird stuff. You've got snow in the Midwest and Plains states where it's got snowfalls, blizzard after blizzard. In Colorado we've seen those pictures. We've got a freeze going out in California, where they're gong to be losing half their citrus crop. If you're out there, of course you're in the middle of it. You know, even in Europe there's been weird weather, if you saw that pictures in the paper today of the storms they've been having in Europe.

There was also a really interesting photo today of helicopters in Austria. The helicopters were going back and forth, ferrying snow from the high peaks in the Alps down to naked ski slopes so that the World Cup ski racers would have something to shush on besides bare rock. They're having ski - having ski tournaments or ski races without the snow. They had to bring them in by helicopter. So the season so far has seemed like anything but typical. But is it really - if you're a meteorologist and you look at this, is this really anything but yeah, maybe every once in a while we get this kind of stuff. You know, it happens. Is it? Other people might say, hey, you know, it's global warming. Certainly over there in the Alps where there are no - there's no snow in the low-lying parts of the Alps, it certainly is global warning.

Well, here to tell us about what he thinks is Kevin Trenberth. He's a senior scientist and the head of the Climate Analysis Section at the National Center for Atmospheric Research - that's NCAR - in Boulder, Colorado. And he joins us today from his office there. Welcome back to the program, Dr. Trenberth.

Dr. KEVIN TRENBERTH (National Center for Atmospheric Research): Oh, hello, and how are you?

FLATOW: Are you snowed in?

Dr. TRENBERTH: No, I just flew in about an hour ago, as it turns out, from San Antonio, where there's a threat of more freezing rain. And here in Boulder today it's bright and sunny but quite cool. It's pretty close to - or pretty close to freezing, I think.

FLATOW: You guys hardly ever get snow in Boulder anyhow. I mean Denver gets really dumped on, doesn't it?

Dr. TRENBERTH: Well, we get over a hundred inches a year, but it doesn't hang around much, and usually it peaks in November, and also in March and April are our really snowy times of year. And of course there's a saying: It's too cold to snow. And that's normally the case in December and January. But this time we have really been dumped on. At my place we got over 60 inches of snow in December. And one of the indications then is that in order to get that amount of snow, it's got to be warmer than normal so that the atmosphere can hold enough moisture.

FLATOW: Well is that - does that not speak for evidence of global warming then?

Dr. TRENBERTH: That's one of the - that's one of the ironical things that people don't understand, I find, about global warming, is that ironically you can get more snow as a consequence, in part, of global warming. And so that may be a little bit of a factor there. And of course at the same time, there was - there was record-breaking heat on the East Coast. And so that was a key part of - certainly a part of the winter that's been going on so far. And as you mentioned, it's - there's been a dearth of snow in Europe and relatively mild conditions.

FLATOW: And talk about California.

Dr. TRENBERTH: Well, you know, just recently we've had a very large cold outbreak and, you know, some of this might just be weather, but the other thing we need to consider - and certainly we talk about it a lot as scientists - is El Nino. And there is a modern El Nino going on, supposedly, out in the Pacific, and that can have a very large influence in the weather patterns, the storm tracks, the atmospheric waves across North America. But it has not been anything like a classical El Nino pattern up until now. We're thinking that the El Nino pattern is really about to kick in and will be with us for maybe the next two or three months.

But - and so that means, you know, potentially more rains for California and especially even Southern California. And maybe the very warm conditions in the East Coast will abate. But generally that does mean cooler conditions in the South but warmer conditions in the northern part of the country.

FLATOW: Now, El Nino - tell us again, that's the warming of the water?

Dr. TRENBERTH: That's the warming of the waters out in the tropical Pacific, east of where they normally occur. So it's out near the dateline and in the central Pacific, and that moves a lot of tropical storm activity, thunderstorm activity, away from where it normally is north of Australia in the Monsoon region and the Indonesian region. And so you're apt to have droughts in Australia, which they've been having, and they've had a lot of wildfires that they are continuing down in the southern parts of Australia now. And also droughts are more likely to occur in Indonesia.

But there's been - there's been some extracurricular activity, if you like, going on, especially in the Indian Ocean this year. And some of that has had an effect in the far West and Pacific. And that's interfered in some ways with the El Nino pattern up till now. You know, there was an outbreak of Rift Valley Fever and some rains in the Horn of Africa, and that's a symptom of more rainfall activity out over the Western Indian Ocean. And the Western Indian Ocean is a region which has warmed up steadily with global warming. And so it's becoming a bigger player, as it turns out, in the global scene.

FLATOW: Does that make - does that make an El Nino more or less important in what goes on with the weather?

Dr. TRENBERTH: It changes the way in which an El Nino gets manifested, and in some places - and certainly in the North Pacific - there's a little bit of a battle. They tend to maybe even cancel each other out a little bit as to some of the effects on where the storm track is going. And presumably that's - you know, what we've had is a result of the combination of these two things. But it looks like El Nino is about to pick up and will hold sway in the next couple of months at least.

FLATOW: That may bring back to normal - us more back to normal.

Dr. TRENBERTH: Normal for El Nino, but still not a normal winter by any means.

FLATOW: And so we might expect more moisture here in the East?

Dr. TRENBERTH: I think the forecast is certainly for more cooler conditions…

FLATOW: Yeah.

Dr. TRENBERTH: …and probably a bit more normal winter-like patterns, I would guess, in the next few weeks at least.

FLATOW: Now, as a meteorologist, you know, we have, oh, 150 years of records or whatever in the databanks. Do you go back - can you go back and say, you know, we've had identical conditions to this year, 1874 or something? And that means - and what happened that year, could that happen this year for the rest of the winter?

Dr. TRENBERTH: People have certainly tried to do that but, of course one of the things which definitely alters things and makes you suspect that there's just no good analog, which is what you're really talking about here, is global warming. You know, and this has really kicked in in the last 25 to 30 years. It's rearing its head more and more, and it just means that conditions nowadays can never be quite like what they used to be in the past. The oceans are warming up. The oceans have warmed up about a degree Fahrenheit as a whole. There's more water vapor over the oceans. That invigorates storms. It changes the character of hurricanes, makes them more intense typically, these heavier rainfall events that we're experiencing across North America.

And so the - you know, this is not - this is not your grandfather's weather anymore.

FLATOW: Let's go to Bruce in Salt Lake. Hi, Bruce.

BRUCE (Caller): Hi, how are you?

FLATOW: How are you?

BRUCE: I've just been experiencing some of this weirdness, maybe more than my share. I just actually flew out of Sweden on Sunday, just as that terrific storm there was starting, and two months ago - we usually do a fall canoe trip on the Green River, which is in the central desert of Utah, and we experienced two days of rain. This never happens in the fall. And this rain broke a 200-year record. And we were camped on a little sandbar, made a rain gauge, and the river was rising at the rate of one inch every 20 minutes, if you can believe that.

FLATOW: Wow.

BRUCE: And that kept on going for about 24 hours, and we had to leave just as dark was approaching because our sandbar was disappearing. But I think you have to take the long view. If you read some of the historical books, for example, about the West, these kinds of freaky patterns are recorded, you know, periodically. And on the other hand, some of the books about early settlers and ranchers, especially in the desert out here, do indicate that over the last 200 years there's been an increasingly dry climate change. And people now are less able to grow crops and run cattle than they were, say, a hundred years ago.

FLATOW: Let me get a reaction, Bruce. Dr. Trenberth?

Dr. TRENBERTH: Well, as we look around the world, there is a pattern of changes in the character of rainfall in particular. Or maybe we should say precipitation. Because one thing that's happening is that there's generally a bit more rain and a bit less snow in many places. And there's been an increase in rainfall at higher latitudes as a consequence because the atmosphere can hold more water if it's a little bit warmer.

Across North America, the statistics for the 20th century indicate that as a whole rainfall, you know, average rainfall, went up a bout 7 percent. But the heavy rainfall, which is actually, let's see, the top 5 percent of events, went up about 14 percent. And the very heavy rainfall, which is the top 1 percent of events, went up at a rate of 20 percent over the 20th century.

Now most of that increase occurred after 1970, and it's an indication that there's more water vapor in the atmosphere so that these storms get invigorated. And that contributes to the kind of event that you referred to, namely that you do get a real golly washer. And it makes water management much of a challenge.

You suddenly have too much of a good thing. And the there are periods in between when you're apt to have drought, and that's especially problem in the Southwest where Lake Powell, you know, went down about 100 feet and has recovered a little bit. But it's still well below what it was before the drought came on about 1999.

FLATOW: And all those people who moved out there, you know, moved out and the building started in a period of relative wetness. Now we've gone back to the drought and there's no water for them.

Dr. TRENBERTH: Well, one of the ironical things in the West in particular is that most of the water rights and the water allocations were set based upon a relatively wet period during something like the first 20 years of the 20th century. And it turns out that's the wettest 20 years we've seen. There's been no 20-year period quite as wet since then.

And so the water is over-allocated, and that's a big issue in the West.

FLATOW: 1-800-989-8255 is our number. Let's see we can get a phone call or two in before we have to go. Gwen in Cambridge, Mass. Hi, Gwen.

GWEN (Caller): Hi. I just wanted to express concern. I've heard, you know, a lot of shows and read newspaper articles and so forth in the past week or so about weather patterns. And the question the reporter always asks is, is this global warming or is this just regular weather?

And the responsible scientists who are asked the question will give a considered answer that's very subtle. And I think it's really important whether these particular patterns have subtleties and connections to El Nino, et cetera, that the scientists always say, yes, global warming is happening and we need to do something about it, and then give their more detailed subtle answer about the specific question they're being asked. Because I think there are still too many Americans who don't understand the urgency that somebody like a Jim Hansen, lead scientist from NASA, you know, on climate, is saying we must act now.

FLATOW: Kevin?

Dr. TRENBERTH: Yes. Well, global warming is happening and it has a pervasive influence on all aspects of weather. But it's more a background influence. All of the variability that we have, all of the storms, are sort of riding on the background of a different underlying conditions. And in particular, as I mentioned before, the sea temperatures are about a degree Fahrenheit warmer globally.

And from year-to-year they can be, you know, locally warmer associated with things like El Nino. And this has a profound effect on the weather patterns and on the rainfall events. You know, so weather is natural. It goes on regardless. Hurricanes are natural. But there is - the way to interpret this I think is that there is a discernible influence on all of these events, of global warming nowadays, and it's effecting drought, it's effecting extreme rainfall events in particular around the world.

FLATOW: Talking about global warming this hour at TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Ira Flatow talking with Kevin Trenberth at NCAR in Boulder.

So you think that this new Congress might have a little more sympathetic view about global warming?

Dr. TRENBERTH: Well, they're certainly scheduling a number of hearings. In fact, I just got an e-mail inviting me to a hearing possibly during the first week of February. Next week I'll be going to Paris on Thursday. And the Intergovernmental Panel on Climate Change, the IPCC, the Working Group I report, which deals with the science of climate change, that will be finalized in an intergovernmental meeting which will finish on the first of February.

And then there's a number of news conferences on the 2nd of February which will announce the findings to the world from the IPCC. And so this is an activity which has involved many scientists over the last two to three years. It's a very rigorous activity with an extensively reviewed report and a lot of negotiations over the exact wording of it.

And so there will be quite a lot of news coming out in just over a week's time about this, and some of that will feed into the hearings that are scheduled on Capitol Hill.

FLATOW: What would be the purpose of the hearings? I mean not to justify the science, would it be?

Dr. TRENBERTH: Well, you know, people say maybe the science has settled if you look at Al Gore's movie or something like that and, you know, we need to do something. But there's really three things that need to be done, I think. One of them is you certainly want to do what is called mitigation. That's related to the Kyoto Protocol. Slow down the increases in greenhouse gases, maybe.

And that's beneficial. But it mainly benefits things in the longer term. The second thing is you need to recognize that global warming is happening and therefore plan for it. And so that recognize the changes that are occurring. And this is referred to generally as adaptation.

And then the third thing I think we need to do is to develop a better information system that actually tracks what is happening with exactly the sorts the things we're talking about. You know, we need better information and the ability to run computer models in near real-time so that we can give you better answers to say exactly whey there is warm conditions on the East Coast at North America at the moment.

And so that's, from a scientific standpoint, an activity which I think needs to be enhanced as well.

FLATOW: All right. Well, we'll watch to see what happens on Capitol Hill, Dr. Trenberth. Thank you for joining with us.

Dr. TRENBERTH: You're most welcome.

FLATOW: Kevin Trenberth is senior scientist and head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colorado.

We're going to take a short break and come back and talk more about what is Congress up to in global warming. Nancy Pelosi has a few things to say, there has been a legislation that just passed yesterday that has to do with effecting climate change. We'll get an insider's view - someone on Capitol Hill who's been through the wars and is still fighting them.

So stay with us. We'll be right back after this short break.

(Soundbite of music)

I'm Ira Flatow. This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News.

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