Two Cold Winters Don't Make A Climate Trend

The polar vortex, a jet stream swirling around the north pole, has weakened the past two winters, allowing plumes of cold air to slip south. But to most climatologists, two years don't make a trend. Atmospheric scientist John Wallace talks about why he is cautious about linking weird weather to global warming.

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IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR. I'm Ira Flatow. A bit later in the hour, how Egyptian protestors are using Facebook and other social media to document their political activities.

But first, here in New York, we got almost two feet of snow dumped on us this week, accompanied by something really unusual, a thunderstorm. It was a record-breaking January.

And earlier in the week, low temperatures had plummeted almost down to zero, but at the same time, there was a warm spell up north over Greenland and the Arctic.

Was this all just a coincidence or not? And could there be any connection to climate change? Joining us to sort through all of this is my guest, John Wallace. He's a professor in the Department of Atmospheric Sciences at the University of Washington in Seattle. Welcome to SCIENCE FRIDAY, Dr. Wallace.

Dr. JOHN WALLACE (Professor of Atmospheric Sciences, University of Washington): Nice to be able to join you.

FLATOW: Was this unusual for you, too, as a meteorologist?

Dr. WALLACE: Well, it reminds me of some other winters I remember in the past, but perhaps in terms of New York City, this must be about as bad as it gets, from what I've heard.

(Soundbite of laughter)

FLATOW: Well, you know, I've lived here my whole life, and I'm looking at the weather charts for today, and I'm noticing that it's gone a little wacky again, the map. It's much warmer in other places and colder in some places.

Are we talking about global warming here, or is it too nebulous to say that?

Dr. WALLACE: Yes, well, I would never associate an event in as short a period of time as a single winter, or even a single couple of years, with global warming, which is a very slow process that's really evolving on the timescale of decades and longer.

FLATOW: So why is it much warmer in the Arctic at this point?

Dr. WALLACE: Right, well, we've had a particular circulation pattern this winter that was really most evident from about mid-December to mid-January, where we had the jet stream that normally comes more or less straight across North America and goes out into the Atlantic, just about over New York, towards England.

And it's usually strong and forms a strong barrier that keeps the cold air to the north and the warm air to the south, but it got distorted in such a way that the cold air was coming down into the eastern United States. And then we had some of the warm air deflected up into Greenland and eastern Canada, and this set up the conditions that are favorable for that cold and snowstorms in the East Coast.

FLATOW: Now, didn't that sort of thing happen last year, also?

Dr. WALLACE: It did, yes, and we recognize it as a recurrent pattern that we can identify in past years, going back even a century. And we can keep track of how often it happens from one decade to another, as well.

FLATOW: So at what point does two years become a trend, something more climatic then?

Dr. WALLACE: Right, well, maybe to give you - illustrate my feeling on that, I maybe I could perhaps mention my own experience in having found what I thought was a trend in this, back with the work of one of my graduate students in the late '90s.

And we had seen a trend towards, in fact, in the opposite sense, toward, in the sense that would give you warmer weather over the eastern United States and northern Europe. We'd seen a trend in that direction for a decade or longer, and we were quite excited about it.

And we actually published a paper mentioning it sort of cautiously, and a number of other people picked up on it, and there were quite a few papers about that back about 10 years ago.

And it turned out no sooner had we pointed this out that nature kind of decided to do something else, and within - by 2005 or so, we could see that this was, in retrospect, it was just a couple of unusual years. It wasn't anything that much.

So I guess I'm inclined to think that history is going to repeat itself here, and that five years from now, we'll look back on these couple of winters and think, well, that was interesting but nothing in way of a trend.

FLATOW: But you do believe that global warming is real, a reality?

Dr. WALLACE: Oh, that's quite a different thing unfolding on a much longer timescale. And there we have - we can employ conventional, statistical methods to separate what's a real trend from just the year-to-year, up-and-down noise.

And of course we have all this corroborative evidence with the changes in melting and freezing dates and independent verification of the temperatures rising both over the oceans, from the ship data, and over land, from the land data, and the upper air temperatures.

So there's a tremendous case there that we have had substantial warming over the - on the period of the 20th century, the last 110 years or so.

FLATOW: And what would account for this incredible flooding that we've seen in Australia? Is there a change in weather patterns there, too?

Dr. WALLACE: Well, this flooding this year was a classic example of what can happen during a strong El Nino year. This is their rainy season. And there is -these very strong events have happened before. There are - there's always records set in certain places when you have some of these strong events.

But I'm not of the impression that this flooding in Australia is unprecedented, and certainly past experience would lead us to believe that the risk of this kind of event would be much greater in a winter like this one, when we have the cold temperatures over the equatorial Pacific and just setting up the weather systems so that there's very heavy rain over that whole part of the world there, not just northeast Australia but parts of Indonesia, Malaysia.

FLATOW: There was speculation going back to the tremendous snowstorms we've been hearing about in Siberia and Europe that there might be the loss of sea ice in the Arctic over this summer might be contributing to not having the ice there, the water evaporates and then dumps its - gets dumped back over there in Europe. What's your thinking about that?

Dr. WALLACE: Well, the time when the ice is actually absent, in the fall, in that part of the Arctic, was pretty limited to mainly the month of October, perhaps in a few places getting into early November. That's before the main snow season.

And even in a mild year in the Arctic, with the exception of Hudson Bay and a few places further south, but the Arctic Ocean as a whole freezes up pretty quickly when you get into mid to late October.

So I don't think that could be a factor that came into play extending into winter to account for, say, the winter - the December snowstorms that we saw in Europe.

FLATOW: Yeah. Let's go to the phones, get a call in or two before we have to leave. Let's go to Jean Paul(ph) in Tucson. Hi, Jean.

JEAN PAUL (Caller): Hi there. This is just an anecdote. I grew up in New York in the '50s, and we lived across from a place called Fort Totten, an old Army base on the north side of Long Island, just at Flushing Bay side.

Anyway, that bay used to freeze over and get so cold, the ice would be so thick that people would drive their cars on it. Plus, I recall that the snowstorms that we would get, we would get a lot of snow.

And I remember the city of New York had huge snow blowers mounted on the fronts of dump trucks, which they would, you know, get rid of the snow. And those snow blowers were, for years, under the highway in mothballs.

So I think - you know, it just points to the cyclical aspect of this, so...

FLATOW: I remember I once interviewed the engineers who designed the George Washington Bridge, and that was built in the '30s, and, you know, it's such a useful - and it's used today as a main artery. So I was wondering: What did they do before the bridge was there? And the engineers said: Well, in the wintertime, we used to walk.

JEAN PAUL: Really? Wow, that's amazing.

FLATOW: Well, there is ice in the Hudson, but then, you know, like you're saying, 60, 70 years ago, it felt like there was a lot more snow and ice. Thanks for calling, Jean Paul.

JEAN PAUL: OK, thanks.

FLATOW: John, do you agree that...

Dr. WALLACE: Yes, and I think we all tend to have short memories, myself included, in somehow thinking of the current events or the events that happened in the past winter or two as being extraordinary compared to anything we've ever seen.

But I think the caller really brought out a good point, that there - and I can remember some experiences of my own, like the winter of January, 1961, hitchhiking up the New Jersey Turnpike and getting stranded actually a couple of successive weeks by snowstorms.

FLATOW: Yeah, so for people who weren't around then, these two winters are sort of a throwback to all those stories we old-timers say: Boy, when I was a kid, we had snow. You know, now we know what that felt like. Would you agree?

Dr. WALLACE: That's absolutely right.

(Soundbite of laughter)

FLATOW: So everybody alive today, who's in their 20s, can say to their grandchildren: Well, you don't know what snow was. You know, these last two -do you expect this trend, would you be surprised or not surprised if this trend continues for another couple of seasons?

Dr. WALLACE: I would be very surprised, and I suspect it'll die a quiet death, and that there won't be any - that you won't be having a program to talk about why it's gone because something new will have happened at that point that's much more interesting to talk about.

FLATOW: OK. I'm going to circle the calendar for next year and put you in on that date.

Dr. WALLACE: Very good, and I'll have to eat - maybe I'll have to eat crow, but I don't think so.

FLATOW: Well, good, we'll talk about the difference. Thanks for taking time to be with us today.

Dr. WALLACE: Thank you.

FLATOW: Good winter to you. John Wallace is a professor in the Department of Atmospheric Sciences at the University of Washington in Seattle, and he was joining us by phone, talking about the old days.

We're going to take a break, and when we come back, we're going to talk about who's tracking your online habits, what links you click on, what you recommend, what's not. We're going to talk a lot about the Internet, social media for the rest of the hour, talk about what's going on in Tunisia and Egypt with the uses of Twitter and Facebook there, how has technology changed the way we communicate, what do we know about you as you communicate.

So stay with us, our number, 1-800-989-8255. You can also tweet us @scifri, @-S-C-I-F-R-I, talk about digital media. So stay with us. We'll be right back after this break.

(Soundbite of music)

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

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