MICHELE NORRIS, Host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.
ROBERT SIEGEL, Host:
And I'm Robert Siegel.
According to weather forecasts, by Friday, it will be over 50 in Boston, and nearly 60 in Washington. So from one end of the Bos-Wash megalopolis to the other, people will be shaking their heads this weekend - hatless in the warm winter sun, of course - they'll be shaking their heads about global warming.
The Web site real climate.org sums up the current dialogue in America about global warming. This way. We now commonly attribute warm weather in the winter to global warming. And then, we are commonly told by the meteorological authorities that we're wrong. It's really El NiÃ±o.
All that Realclimate.org, Penn State meteorologist Michael Mann sets out to reconcile those explanations. And he joins us now from State College. Welcome to the program professor Mann.
MICHAEL MANN: Hi, Robert. Good to be with you today.
SIEGEL: And first point, for those who say, well, it's a mild winter in the east, but look at all the snow out in Denver. Actually, that doesn't cut against the grain of it being a very warm winter?
MANN: No. It doesn't. There's a misconception that the sort of weather that's been experienced out there this winter that it contradicts the observation that we've seen of anomalous warmth in most parts of the country. And in fact, that's not quite the case. If you look at Colorado, the past month, for most Colorado, it was also above average. And in fact, as long as it's cold enough to snow, warmer temperatures can actually favor increased snowfall, because warmer air that has been equal, contains more moisture within it.
SIEGEL: Well, you are a meteorologist, so we would expect you to be one of those telling us this is really about El NiÃ±o, not about global warming or manmade global warming. But you don't say that. You don't say it's all El NiÃ±o. Why not?
MANN: Well, we have to realize that the weather, just sort of like a pair of dice, involves both random and deterministic components with the state of the atmosphere that we have, but the random element - that's the weather, and we have the deterministic factors: El NiÃ±o, climate change, factors that can sort of bias the weather that push it in one direction or another on the average.
SIEGEL: But what is it about the temperatures that say, we've experienced on the East Coast of the United States that stand out to you and say, that's not just El NiÃ±o at work?
MANN: If you look at a typical El NiÃ±o pattern, you see a warmer than average temperatures over most of the northern half of the U.S. But you actually see colder temperatures, typically, in other parts of the U.S. It's a different pattern from what we've actually observed both so far this winter. And certainly, what we saw last winter, which was not an El NiÃ±o year anyway, where the entirely U.S., essentially, it was warmer than average for the duration of the winter.
So there's something more. El NiÃ±o usually leads to an elevation of one or two degrees Fahrenheit in the average temperatures over large parts of the U.S. So far this winter, we're seeing temperatures that are more like five to 10 degrees Fahrenheit warmer than average.
SIEGEL: But those increases in temperature are also higher than any of the increases you hear people talking about when they describe global warming. So what do they reflect, if they reflect neither global warming nor El NiÃ±o?
MANN: Part of the unusual warmth that we've seen this winter is almost certainly just due to the vagaries of weather, the randomness. But that weather is being pushed in certain directions systematically towards warmer temperatures over part of the U.S. by EL NiÃ±o and warmer temperatures over the entire U.S., something that's favored by climate change. So I think it will be last two winters, and the dice-rolling analogy is we just came up snake eyes - two ones. The chance of that happening randomly is about one in 36. But if you raise all the numbers from two to five on those dice, you'll find that you roll snake eyes 70 percent of the time. So we could simply be seeing the loading of the dice.
SIEGEL: Is climate change, when you use it here in this discussion, synonymous with climate change in someway induced or created by human activity, or is there simply climate change that takes place without any clearly, human cause.
MANN: We're talking about a change in the statistics of the climate, and that change in the statistics could be due to anthropogenic, that is human factors, in particular, the increase of greenhouse gas concentrations in the atmosphere, to the fossil fuel burning, or it could be due to slow changes in deterministic elements, changes in the output of the sun. The coming and going to explosive volcanic eruptions. Changes in these factors can also give this climate change.
But one thing we know is that there is no way to explain the trends that we've seen over the past one to two decades in terms of any of these natural factors. So in that context, when we talk about recent climate change, we're really talking about anthropogenic climate change, humans.
SIEGEL: Professor Mann, thank you very much for talking with us.
MANN: Thank you Robert it was great talking with you. That's meteorologist, geoscientist Michael Mann, who is the director the Penn State Earth System Science Center. He spoke to us from State College, Pennsylvania.
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