Air Date: Week of March 6, 1998

The weather pattern El Niño has killed hundreds of people and inflicted millions of dollars in damage this winter. From floods in California and Peru, to high winds in Florida and Mexico, and the freak ice storm that devastated eastern Canada and northern New England, the drought in South east Asia may also be linked. While El Niño is a natural phenomena, some scientists suspect that recent shifts in its pattern is a response to human-induced global warming. Steve Curwood speaks with Kevin Trenberth heads the Climate Analysis Section of the National Center for Atmospheric Research in Boulder, Colorado.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood.

El Niño. The weather pattern has killed hundreds of people, and inflicted millions of dollars in damage this winter from floods in Peru and California to high winds in Mexico and Florida. A freak ice storm that devastated eastern Canada and northern New England may also be linked to El Niño. In the meantime, New Yorkers note that this is the first year since records have been kept that there has been no snow in Central Park during February. And at the same time, halfway around the world drought has racked southeast Asia. While El Niño is a natural phenomenon, some scientists suspect that recent shifts in its pattern are responses to human-induced global warming. Kevin Trenberth heads the Climate Analysis Section of the National Center for Atmospheric Research in Boulder, Colorado.

TRENBERTH: El Niño has been behaving unusually in, say, the last 20 years compared with the previous hundred years. And so that gives us pause. That makes us really ask that question as to whether what we are seeing might be a part of the global warming signature.

CURWOOD: What's new about El Niño's behavior?

TRENBERTH: Well, traditionally, we have an El Niño event, which is a warming of the tropical Pacific, interspersed with its sister, the La Niña, which is a cold event in the tropical Pacific. And in historical times these have occurred about every 3 to 7 years, alternating from one to the other. In the last 20 years we have seen a lot more El Niño events, and we've also seen bigger and longer El Niño events than we have historically. And so, this is the reason why we ask that question.

CURWOOD: So you're saying that if you look back over the record of 100 years, the most recent 20 are quite a bit different.

TRENBERTH: That's right. Since about 1976.

CURWOOD: Have you done any statistical analyses of this? I mean, what are the odds that the present El Niño pattern is just, you know, a random walk?

TRENBERTH: This requires firstly getting good information on what has happened in the past, and that is not an easy thing in itself. And so, using the best information we have, we have done some sophisticated statistical analysis, which indicates that given the previous hundred years, what's been happening is about a 1 in 2000 event. And so, it is sufficiently rare that it looks like global warming must be playing a role or some other form of climate change must be playing a role, and then the next question is, what is that role?

CURWOOD: Could you please explain to us briefly how global warming could affect the El Niño?

TRENBERTH: Well, one of the things global warming does is, at high latitudes it mainly affects temperature. And a lot of people think global warming just refers to increases in temperature. It's really much more than that. In the middle and low latitudes, in the tropics in particular, most of the heating, the additional heating that goes on, goes into evaporating moisture. And that means that in places where it's dry, where a drought is occurring, say, for natural reasons or associated with El Niño, things dry out more quickly, and so the drought is more severe, longer lasting, more intense. Secondly, because there's more moisture in the atmosphere, that moisture gets sucked up into whatever weather systems there are, whether they are thunderstorms, whether they are rain storms, mid-latitude cold fronts, and there's more moisture available to all of those systems. And so we get heavier rains, and we've seen a lot of evidence that indeed, it is raining harder, especially across the United States, when it rains, than it has historically. And so because El Niño causes floods and droughts and redistributes those around the world, the intersection with one of the main manifestations of global warming may be simply that the droughts and the floods become more severe.

CURWOOD: From your work, Dr. Trenberth, do you think that we're in trouble? That the human-induced climate change is putting us on a course that we're going to find even worse weather than we've seen in the El Niño problems this year?

TRENBERTH: I think the biggest changes that we really need to watch out for, and which we have probably not paid enough attention to, are the changes in extremes. Those are the main ways in which we will actually notice global warming. We won't notice a one-degree change in temperature. What we will notice are when it gets extremely hot in summer and there are heat waves, or there are extremely dry conditions and we have droughts, as we have had in Indonesia, record-breaking conditions over there. And floods, such as we've seen in California and even Florida, very recently. And it's impossible to say, point your finger at any one event and say yes, this is caused by global warming. But global warming's probably contributing a little bit to all of these things. And if El Niño becomes the norm, and it may be that there are shifts in population that result from this kind of thing.

CURWOOD: Well, I want to thank you for taking this time today.

TRENBERTH: Thank you.

CURWOOD: Kevin Trenberth heads the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colorado. He spoke to us from member station KGNU.