Fortune has a good article on the risk of rapid climate change. Many people think of climate change as a gradual process spanning over decades. In this article they discuss the risks of radical changes to the climate happening in the span of a few years.
Climate researchers began getting seriously concerned about it a decade ago, after studying temperature indicators embedded in ancient layers of Arctic ice. The data show that a number of dramatic shifts in average temperature took place in the past with shocking speed—in some cases, just a few years.
One looming concern is not warming, but actually having the ocean thermal conveyor that keeps Europe mild shutting down. This might help explain European's more proactive approach to climate change mitigation. But, I think that the structure of European economies (less CO2 intensive economy per capita) vis-a-vis the US and public attention to the issue are more the drivers.
The eastern U.S. and northern Europe, it seems, are warmed by a huge Atlantic Ocean current that flows north from the tropics—that's why Britain, at Labrador's latitude, is relatively temperate. Pumping out warm, moist air, this "great conveyor" current gets cooler and denser as it moves north. That causes the current to sink in the North Atlantic, where it heads south again in the ocean depths. The sinking process draws more water from the south, keeping the roughly circular current on the go.
But when the climate warms, according to the theory, fresh water from melting Arctic glaciers flows into the North Atlantic, lowering the current's salinity—and its density and tendency to sink. A warmer climate also increases rainfall and runoff into the current, further lowering its saltiness. As a result, the conveyor loses its main motive force and can rapidly collapse, turning off the huge heat pump and altering the climate over much of the Northern Hemisphere.
What I find interesting is that US Government strategic planners are now seriously contemplating the geo-political effects of rapid climate change. What would happen if much of Western Europe froze, and agricultural belts shifted worldwide?