Posted on Friday, December 09, 2005 5:01 PM
Sometimes you read a science paper and it makes you want to curl up in a corner and suck your thumb for a while. This paper in
nature (December 1st 2005) by Bryden
et al. is a perfect example.
A large part of our climate is determined by heat transport by the ocean water, water warms up at the tropics, gets transported North. The warm water releases its heat gradually and, cools down and gets denser, sinks and gets transported back South in deep ocean currents. Think of it as our European central heating system, this warm current contributes significantly to the temperate climate in Western Europe.
This process is affected by temperature of course, but also the salinity of the water will influence its density and therefore its circulation. One effect of global warming will be that more fresh water is injected into the ocean in the North as a consequence of the melting of the ice caps or increased rain fall. This will result in a decreased density of the water in the North, and that may cause problems for the overturning circulation of water.
Bryden et al. have taken measurements at five intervals in five decades and their results show a worrying decrease in the overturning circulation of 30%! These findings match with the results of other studies and climate models, and most importantly provide direct observations of this trend that has been predicted.
So what does it mean? Possibly, when a certain threshold is reached the overturning circulation will stop altogether, causing an abrupt drop in air temperature in NW-Europe of 10 degrees C. I sure hope that the people at the UN climate conference in Montreal are reading this. Though I have a nagging feeling the USA delegation will not care too much. who knows! Their climate may actually improve…
In the mean time I am knitting sweaters.