Global warming: freezing Europe

One of the big worries of climate change is what the scientists call "large-scale, high-impact, non-linear and potentially abrupt changes in physical and biological systems" - things like, say, the Greenland ice-cap melting, the West Antarctic ice-sheet sliding into the sea, or a shutdown in ocean convection. And now it seems like some of this is actually happening. According to scientists at the UK's National Oceanography Centre, the Gulf Stream is slowing down. Measurements in Florida and from a series of sensors positioned across the Atlantic have detected a 30% decrease in cold, deep return currents - which means a consequent weakening of the warm surface currents flowing past and warming Europe. More data needs to be gathered (more data always needs to be gathered), but the change is out of phase with the usual long-term pattern of variability, and exactly what you would expect from the increased melting of Greenland's glaciers.

The Gulf Stream has a significant effect on Western Europe's climate, keeping it artificially warm compared to landmasses at the same latitude (such as Newfoundland). A total shutdown would cool Europe by between four and six degrees Celsius. While this wouldn't mean an instant ice age (as portrayed in The Day After Tomorrow), it would mean a gradual growth of snow-cover and a significant decline in agricultural production - not to mention a lot of cold people. The slowdown so far detected won't be as bad, and is only expected to cool Western Europe by about a degree over the next couple of decades - but even that is bad enough. By way of comparison, the "Little Ice Age", which caused increased glaciation and widespread famine and flooding (not to mention a population crash in Iceland and the extinction of Greenland's Vikings), is estimated to have resulted from a change of less than 1^o C, and probably only half that.

There's an inescapable irony in the prospect of Europe being frozen due to global warming - but that's how non-linear systems work. Meanwhile, other parts of the world will almost certainly enjoy an increase in temperature. The heat from the Gulf Stream has to go somewhere, and is likely to end up in the weather system - potentially disrupting the climates of the Caribbean, Central America, and West Africa. It is also likely to result in warmer ocean temperatures in the mid-Atlantic and Caribbean, the spawning grounds for Hurricanes. We've already seen a record hurricane season this year, and we may see worse in the future.