Date published: 2007/08/17
The BBC says:
Scientists have painted the first detailed picture of Atlantic ocean currents crucial to Europe's climate.
Using instruments strung out across the Atlantic, a UK-led team shows that its circulation varies significantly over the course of a year.
Writing in the journal Science, they say it may now be possible to detect changes related to global warming.
The Atlantic circulation brings warm water to Europe, keeping the continent 4-6C warmer than it would be otherwise.
As the water reaches the cold Arctic, it sinks, returning southwards deeper in the ocean.
Some computer models of climate change predict this Atlantic Meridional Overturning Circulation, of which the Gulf Stream is the best-known component, could weaken severely or even stop completely as global temperatures rise, a scenario taken to extremes in the Hollywood movie The Day After Tomorrow.
Last year the same UK-led team published evidence that the circulation may have weakened by about 30% over half a century.
But that was based on historical records from just five sampling expeditions, raising concerns that the data was not robust enough to provide a clear-cut conclusion.
The key for scientists, then, has been to measure and understand how the circulation varies naturally, making it much easier to pick out any changes related to man-made global warming.
This has been the goal of the Rapid/Mocha (Rapid Climate Change/Meridional Overturning Circulation and Heatflux Array) project; and its first results show that the circulation varies substantially, by a factor of eight, even during a single year.
"I think this is a major step forward for our understanding of ocean circulation," said Stuart Cunningham from the National Oceanography Centre (NOC) in Southampton, one of the project's senior scientists.
"The Atlantic Ocean carries a quarter of the global northwards heat flux, so having the information to plug into climate models will be a major adddition," he told the BBC News website.
But measuring long-term variation is, if anything, even more important. Man-made warming could drive the flow downwards, but so could natural climate cycles such as the Atlantic Multidecadal Oscillation.
All five of the historical flow values documented in last year's paper, for example, fit within the range of variability measured here, making it very hard to argue that these observations found a long-term trend.
It just goes to show how silly it is to jump to hysterical conclusions based on little evidence. The factor of eight variability in one year is amazing, and will make figuring out long-term trends extremely difficult.
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