MARGARET WARNER: Now, rapid warming leads to record melting in the Arctic.
Ray Suarez has the story.
RAY SUAREZ: The seasonal shrinkage in Arctic ice is more extensive than ever before, as seen in this animation. The rate of melting increases in the spring and summer months and reaches its peak in September.
According to the National Snow and Ice Data Center, the low point came on Sunday, when ice covered just 24 percent of the Arctic Ocean. the previous low of 29 percent was set in 2007.
Walt Meier is a research scientist at the National Ice and Snow Data Center. His work specializes in sea ice and its impact on climate.
And, Walt Meier, as we mentioned, there's always a freeze-and-thaw cycle during the year. What was different about 2012?
WALT MEIER, National Snow and Ice Data Center: This year was different, in that it was the lowest we have ever seen in our satellite record, which dates back to 1979.
And it kind of -- it puts an exclamation point on a long-term trend that we have been seeing over those years since 1979 of less and less sea ice at the end of each summer. And this year was much less than anything we had seen before.
RAY SUAREZ: When you talk about a long-term trend, how far back do the records go of close observation of the amount of cover?
WALT MEIER: The close observation we have, the complete satellite record that we have starts in 1979. And that's where we have very high confidence, very complete data.
Before that, the data is not quite as complete as we have after that, but we do have some records that go back to the 1930s.
RAY SUAREZ: Are there other kinds of evidence that you can look at to infer the ice cover, other kinds of physical evidence that go back further than '79?
WALT MEIER: Yes, we do have what are called paleo records, which are based on things like ice cores or, in the case of sea ice in particular, sediment cores that we can take from the Arctic Ocean, the bottom of the Arctic Ocean.
And the sediment is different under ice vs. under open ocean, particularly because of the organisms. There's different organisms that live in the open ocean vs. that live in the ice, and when they die they fall on to the ocean bottom.
And those records go back several thousand years and tell us not a complete picture, but a pretty good idea of what the conditions were like in general going back to that time period.
RAY SUAREZ: Now, Walt Meier, this is a part of the world where I would guess 99 percent of humanity will never venture. Is there anything that goes on up there as far as ice melt and refreezing that has an effect on what happens in the skies over the United States?
WALT MEIER: Indeed, there is.
The Arctic sea ice, essentially, it is a big reflector of solar energy during the summer, and that keeps the Arctic cooler than it normally would be. It acts like an air conditioner in a sense for the Earth's climate system. And that helps not only keep the Arctic cooler, but also the globe as well.
And it's basically a sink for heat that comes in at the equator, gets transported to the north.
And then you lose the heat in the Arctic. And those -- that transfer of heat from the equator to the poles, that essentially helps set up things like the jet stream, our prevailing winds, our weather tracks.
And so as we start to lose the ice cover and we warm up the Arctic, essentially, that's changing the balance between the equator and the poles. And that will shift things like storm tracks and the jet stream, and that will change weather patterns.
And we have seen some evidence of that already, and we expect to see more in the future, although we're still in the early stages of understanding that completely.
RAY SUAREZ: You know, it's commonplace in stories that are written about what's happening in Greenland, what's happening in the Arctic Sea that it's happening faster than climate scientists had predicted in their models. What's the significance of that?
WALT MEIER: Well, I think there's a couple things that it may -- that it means.
One is that the models may not be fully capturing all the processes and the speed of the processes that are occurring in the Earth's climate system.
There's also probably some role in terms of the natural variation of the climate, that you could have times where things speed up a little bit more and other times where they slow down, and the models don't necessarily catch all those kind of speed-up and slow-down periods.
They're just looking at kind of the long-term trends. But we are seeing things go much faster than what the models had projected. The models had suggested that we may see a summer without -- with very little ice by the end of this century.
That's something that, you know, our grandchildren or even great-grandchildren might have to deal with. But now we're looking at perhaps within 20 years. And that's something that many of us alive today will be having to adapt to and those changes that will be a result of that.
RAY SUAREZ: Should we assume it's going to be even worse next summer, next September?
WALT MEIER: We can't do that, because there's a lot of variation from year to year in the Arctic sea ice and in climate in general.
And, typically, we do see kind of ups and downs along this kind of overall declining trend and actually accelerating trend in recent years.
But, oftentimes, after we hit a record low, we will see things bounce back. And it may be even kind of stable for several years. We don't foresee going back to the levels we were back in the 1980s, but we may see things level out for a while before dropping again.
RAY SUAREZ: Walt Meier of the National Ice and Snow Data Center, thanks for joining us.
WALT MEIER: All right. Thank you.