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JACKI LYDEN, host: This week on NPR, we've been hearing about a possible rush for Arctic resources, as well as possible conflicts as the northern sea ice melts away. The latest science finds that the transition to open summertime waters is likely to be chaotic and the consequences will stretch far beyond the Arctic. NPR science correspondent Richard Harris has the final report in our series.

RICHARD HARRIS: The Arctic sea ice has always seen dramatic swings. In fact, every winter the ocean is completely covered with ice, and by September about half of that ice has melted away, exposing vast stretches of open water. And now, add to that annual gyration a more recent trend. Mark Serreze, who runs the National Snow and Ice Data Center at the University of Colorado, says the seasonal melt has been claiming more and more ice since at least 1979, when they started monitoring that trend from space.

MARK SERREZE: Within the satellite record, this is the lowest ice extent for July that we've ever seen.

HARRIS: In fact, we're not far from the 2007 record-low for seasonal ice loss.

SERREZE: The Arctic keeps surprising us. The point is we're losing the sea ice faster than we think we ought to be. And this is causing us to revise some of our estimates.

HARRIS: Just a few years ago, scientists forecast that global warming would clear summer ice from the Arctic Ocean by the year 2100. Now, many forecasts say that could happen in the middle of this century. And Serreze says a few peg that ice-free spell as early as 2030.

SERREZE: I think that's a reasonable estimate.

MARIKA HOLLAND: We very likely will live to see ice-free summers in the Arctic. Or if we don't live to see it, our children will.

HARRIS: Marika Holland at the National Center for Atmospheric Research says nobody can pinpoint a date because Arctic ice is hard to predict year-to-year. That unpredictability has implications for people who are thinking about exploiting Arctic resources and expanding Arctic sea routes.

HOLLAND: Some of these shipping routes will become open much more reliably. But we're not close to that yet and we can't predict exactly when that's going to happen.

HARRIS: The sea ice is at the mercy of currents, cloud patterns and a host of other variables that change naturally from year to year.

HOLLAND: We could have instances of very rapid sea ice loss. Those might be followed, for years or even a decade, by quite stable sea ice conditions. But it's difficult to predict exactly when these instances of very rapid sea-ice loss could occur.

HARRIS: The consequences of melting ice are going to be felt first in the Arctic region. For example, polar bears and walruses rely on sea ice as hunting platforms and places to rest, and as those ice edges move out into deeper water, farther from the shore, that makes it harder for those animals to make a living. Leonid Polyak, from the Byrd Polar Research Center at Ohio State, says wildlife had to face a temporary warm spell in the arctic about 8,000 years ago, when it was actually hotter than it is today. But this time is different.

LEONID POLYAK: Significant changes in the ice cover will affect the ecological system very profoundly. And it's not given that, you know, many of those species will survive if Arctic ice disappears completely in summer.

HARRIS: And the changes aren't just to wildlife. The ice serves as a giant reflector for energy, so as it melts away, the ocean water will absorb more heat and drive up the temperature on nearby land masses. In the coming decades, the frozen ground that makes it relatively easy to get around in the Arctic will start turning to mush. And Marika Holland says the effects of Arctic warming will gradually reach farther south.

HOLLAND: What happens in the Arctic affects, you know, heat waves in Chicago or elsewhere.

HARRIS: And let's not forget global sea-level rise, which isn't as obvious an effect as you might think.

HOLLAND: Sea ice melt directly doesn't affect sea level.

HARRIS: After all, your lemonade doesn't overflow when the ice that's floating in it melts. But the concern here is what will happen to the ice that's piled up on Greenland bedrock.

HOLLAND: If we see this enhanced warming due to sea-ice loss, we'll very likely start to melt more of the Greenland ice sheet. That water does lead to sea-level rise.

HARRIS: And those global impacts are going to be much more noticeable to us than the changes that will gradually reshape the Arctic. Richard Harris, NPR News.

(SOUNDBITE OF MUSIC)

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