ROBERT SIEGEL, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.
Scientists who keep an eye on the earth's rising temperature are looking to see what that's doing to the oceans. They've seen plenty of action in and around the arctic, melting ice, more rain and disappearing glaciers. And all that melting means that there is a lot of water on the move.
NPR's Christopher Joyce talked to some scientists about this arctic deluge and what it might mean for the world's climate.
CHRISTOPHER JOYCE reporting:
The Artic Ocean sits on top of the world. It's covered in sea ice a lot of the time and very few people live nearby, so it doesn't get too much attention except from hearty types like climate scientist Max Holmes. Holmes spends a lot of time in Siberia measuring freshwater rolling into the Arctic Ocean from rivers like the Ob, the Yenisei and the Lena, rivers most Americans have never heard of.
Mr. MAX HOLMES (Climate Scientist): Essentially, the Ob, Yenisei and Lena are all comparable in size to the Mississippi. They're basically right next to each other, pouring in incredible amounts of freshwater.
JOYCE: In fact, for close to half a century the flow from arctic rivers and from rainfall has increased dramatically, an extra 20,000 cubic kilometers worth of new freshwater. That's equivalent to about 40 years worth of the water that flows out of the Mississippi. There's also more freshwater coming from sea ice in the Arctic Ocean that's been rapidly melting, and there's yet more freshwater coming from melting glaciers. What Holmes has tracked is where all that water has gone.
Down into the North Atlantic.
Mr. HOLMES: I think the amazing thing is that over about this 40- or 50- or 60-year timeframe, we can look north from the North Atlantic, we can look up into the arctic and find where most of this freshwater's come from.
JOYCE: Holmes works at the Woods Hole Research Center in Massachusetts and is part of a team that reports these findings in the journal Science. The researchers note that other scientists have already documented this trend. What the new study does is measure it and confirm where the water is going.
What they still don't know is how that freshwater will affect the circulation in the Atlantic, especially what's called the meridional overturning circulation. It's easier to call this the conveyor belt of the Atlantic. Essentially warm water from the South Atlantic moves north and warms big parts of northern Europe. The conveyor belt has a big influence over European weather, and Holmes says the new slug of freshwater from the arctic could bollocks that up.
Mr. HOLMES: My concern is if you add enough extra freshwater to the north Atlantic, you could slow down or even shut down the circulation which would potentially have dramatic impacts on climate, such as a cooling in the North Atlantic region in Western Europe. So a kind of surprising response to global warming, where you can actually get regional cooling in parts of the globe.
JOYCE: The Atlantic Ocean conveyor belt has slowed or stopped before, tens or hundreds of thousands of years ago. Climate scientist Jonathan Overpeck at the University of Arizona says those events were due to much bigger melting episodes.
Mr. JONATHAN OVERPECK (University of Arizona): We have good estimates of when this occurred, you know, when big slugs of freshwater got into the North Atlantic and affected the circulation, shut it down. These were very large compared to what is happening now, but nonetheless some scientists, myself included, are worried that the North Atlantic could be quite sensitive to the smaller amounts of freshening that are occurring now.
JOYCE: What Overpeck and other scientists have not measured yet is how much freshwater is now coming from Greenland. Vast ice sheets there are the King Kong of the Atlantic, says Overpeck, tied up in ice for now but starting to melt and come apart.
Mr. OVERPECK: Add in the melting disintegration of Greenland and you are talking about quite a bit more fresh water than we have now. And I don't think anyone can say with confidence that we're safe from a large scale abrupt change in the North Atlantic.
JOYCE: Nothing imminent, he says, but worth watching out for.
Christopher Joyce, NPR News.
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