The Atlantic Ocean's flow between the tropics and cold, northern waters appears to be weakening, which could drastically alter the weather in Europe, a newly released study shows.
The findings, published in the journal Nature, found that the Atlantic Conveyor flow slowed by about 30 percent between 1957 and 2004.
The cycle of flow, technically known as the "Atlantic meridional overturning current," plays a key role in warming northern Europe.
The key is the Gulf Stream. After it emerges from the Caribbean, it splits in two, with one part heading north-east to Europe and the other circulating back through the tropical Atlantic.
As the north-eastern branch flows, it gives off heat to the atmosphere, which in turn warms European land.
Computer models of climate have regularly predicted that the North Atlantic conveyor may well reduce in intensity or even turn off altogether, a concept that was pushed beyond credence in the Hollywood blockbuster The Day After Tomorrow.
The North Atlantic is dominated by the Gulf Stream – currents that bring warm water north from the tropics. At around 40° north – the latitude of Portugal and New York – the current divides. Some water heads southwards in a surface current known as the subtropical gyre, while the rest continues north, leading to warming winds that raise European temperatures by 5°C to 10°C.
The slow-down, which has long been predicted as a possible consequence of global warming, will give renewed urgency to intergovernmental talks in Montreal, Canada, this week on a successor to the Kyoto Protocol.
In sum, Europe is kept at a higher temperature than eastern North America by the waters from the Gulf Stream. The flow northwards however, appears to be shutting down, which means Europe will likely soon experience local reduction in temperature.
Doesn't that contradict global warming?
No. Global warming refers to a WORLDWIDE increase in AVERAGE temperature. Even if Europe is cooling, the rest of the world appears to be warming faster, and more than makes up for one small region of the world cooling instead. Keep in mind the following three key terms:
Weather - local changes in temperature, humidity, etc. that vary from day to day (e.g., sunny, rainy, windy, snowing). This is what little kids learn about in kindergarten.
Climate - average weather for a large area (portions of continents) over longer time scales (decades to centuries). Daily changes (sunny one day, cold the next) don't make a difference in climate; even if one year is colder or warmer than the last doesn't change the climate. Climate may be different in different parts of a continent (e.g., Africa contains both desert and rain forest), but two neighboring towns will not have different climates.
Global climate - averaging the weather/climate information for the entire planet over long time scales. Historically the global climate typically took centuries to change, except when in catastrophic circumstances, such as huge volcanos or asteroid/cometary impacts. The whole of the Earth has the same global climate, so the only way to spatially change the climate is to go to a neighboring planet. Venus and Mars actually have remarkably similar climates to ours, and the three planets are often referred to as the Goldilocks Problem by astronomers - "This planet (Venus) is too hot! This planet (Mars) is too cold! This planet (Earth) is just right!"
However, there are two additional complicating factors. There always are.
Shut-off of the Gulf Stream flow may be the result of global warming.
Nobody is clear on what has gone wrong. Suggestions for blame include the melting of sea ice or increased flow from Siberian rivers into the Arctic. Both would load fresh water into the surface ocean, making it less dense and so preventing it from sinking, which in turn would slow the flow of tropical water from the south. And either could be triggered by man-made climate change. Some climate models predict that global warming could lead to such a shutdown later this century.
The last shutdown, which prompted a temperature drop of 5°C to 10°C in western Europe, was probably at the end of the last ice age, 12,000 years ago. There may also have been a slowing of Atlantic circulation during the Little Ice Age, which lasted sporadically from 1300 to about 1850 and created temperatures low enough to freeze the River Thames in London.
Anyways, the data is still fresh and hasn't yet been confirmed by other groups (peer reviewed).
But Richard Wood, chief oceanographer at the UK Met Office’s Hadley Centre for climate research in Exeter, says the Southampton team's findings leave a lot unexplained. The changes are so big they should have cut oceanic heating of Europe by about one-fifth – enough to cool the British Isles by 1°C and Scandinavia by 2°C. "We haven’t seen it yet," he points out.
Though unseasonably cold weather last month briefly blanketed parts of the UK in snow, average European temperatures have been rising, Wood says.
So don't get your knickers in a twist yet and say global cooling is happening, you can reserve your judgement. Don't breathe a sigh of relief yet either, claiming that the world is safe either way - it sounds to me like most of the world will fry, but Europe will freeze. Me, I'm gonna play it safe and move to Europa, at least the temperature's a pretty consistent 103K (-170ºC). You always know what to wear for the weather there: a space suit!