Ocean currents transfer warm and cold water across the globe, significantly influencing temperatures of nearby land. Host Steve Curwood speaks with Scottish oceanographer William Turrell on a recent discovery that one segment of this ocean circulation in the Atlantic may actually be slowing down - which could lead to a colder northern Europe.
CURWOOD: Deep ocean currents in the Atlantic keep Northern Europe warmer than what might be expected. For years, climate scientists have predicted that climate change could disrupt this circulation and actually make parts of Europe colder. Now, new research from a team based in Scotland shows that this circulation is indeed slowing. But scientists say it's too soon to conclude if this is the result of human-induced climate change. William Turrell is an oceanographer with the Fisheries Research Service's Marine Laboratory in Aberdeen, Scotland. He explains the research took place in a narrow passageway between Scotland and the Faroe Islands to the north.
TURRELL: It's part of the thing called the global conveyor belt, but it's the sort of northern limb of that conveyor belt. It starts, say, in the Gulf Stream, where warm surface water flows up the coast of the States. Then some of it crosses over to Europe in the North Atlantic current, and then some of that flows into the Arctic Ocean, past the north of Scotland, between Scotland and Faroe. It then goes into the Arctic ocean, where it's cooled every winter and sinks, and then in comes back out as cold water near the bottom of the sea. And again, that cold outflow flows, again, back out through a gap between Scotland and Faroe. So, we sit either side of this key area in the circulation of the North Atlantic and Arctic.
CURWOOD: How does this North Atlantic circulation affect the European climate?
TURRELL: It's very important, particularly for the Northern European and Scandinavian climate, because that warm surface inflow brings with it a lot of heat. And each winter, as the water is cooled and sinks, of course, when it cools, what it means is it's giving its heat to the air. And then the air blows over Northern Europe and Scandinavia, keeping us moderately warm compared to places as far north as us, such as Alaska and Siberia.
CURWOOD: What did you find in your research?
TURRELL: Well, we've been monitoring since 1994, the cold bottom, or the outflow. And since about '94 we saw about a 5 percent decrease in that outflow. We then went up to Ocean Weather Station Mike, which is a station in the Norwegian Sea. There they have data from the 1950s. So by combining the modern measurements with the older measurements, we've been able to extrapolate the results back in time, and over the last 50 years we've found that the overflow from the Arctic has decreased by about 20 percent.
CURWOOD: What does this mean, a decrease in flow by 20 percent?
TURRELL: Well, the obvious implication is that if the outflow has decreased by 20 percent, so has the inflow, the inflow of warm water at the surface. So the delivery of heat to Northern Europe will have decreased by 20 percent.
CURWOOD: Your research organization has data going back for more than a hundred years covering this gap. What do you know from that ancient research?
TURRELL: All we can really say is that the changes we're seeing that commenced in the '50s really didn't occur in the previous part of the century. A hundred years is really nothing in terms of climate. There are other records, like the Greenland ice core record, where you can go back a lot further in history, go back hundreds of thousands of years. And over that period we know that these sort of changes in the Northern Europe climate have occurred many, many times before, before man ever came on the scene. So this could be just part of a natural-- not cycle, because that implies it happens regularly, but a natural episode that has happened before.
CURWOOD: What does your research tell us about the rate of this change?
TURRELL: Only that over 50 years it's decreased 20 percent. We can't extrapolate into the future. We know that these systems can recover so that the outflow may again strengthen again. We know that it may keep reducing at the same rate. So really, the only thing we can do is monitor, keep our measurements going, and see what happens. The next decade will be fairly crucial. We'll know whether it's going to continue or whether it's going to recover.
CURWOOD: What links between this drop in flow in the ocean circulation and temperature change, climate regime change in Europe have been observed to this point?
TURRELL: The one direct link we think at the moment is that the air temperature in Faroe and possibly in Northern Norway, is, if not cooling at the moment, it is not showing the warming that everywhere else is showing. So already we think that there may be evidence of a reduced supply of heat to the air around Faroe and to the climate of Faroe. So that's, at the moment, the only direct link between the change in the outflow and atmospheric climate we've seen.
CURWOOD: Warming elsewhere? Could you explain, please?
TURRELL: Well, throughout the Northern Hemisphere, in fact, throughout the globe, the norm at the moment is for air temperatures to be warming. One of the few exceptions is in Northern Scandinavia and Faroe where it looks like air temperatures aren't following that global trend.
CURWOOD: Now, how could human-induced climate change, if it happens as the models predict, be affecting this circulation of water that you're seeing?
TURRELL: The only way, really, that anthropomorphic climate change could affect it would be by the supply of fresh water to the Greenland Sea area. We think that the sinking has stopped because there's more fresh water in that area. And that might be associated with, say, melting ice in the arctic. But that is beyond our own research; we can't really say anything about what's causing the outflow to slow down.
CURWOOD: William Turrell is an oceanographer with the Fisheries Research Services Marine Lab in Scotland. He spoke to us from Akureyri, Northern Iceland. Thank you sir.
TURRELL: Okay, thanks.
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