Warmer and wetter

One of the arguments put forward by global warming sceptics has just been dealt another blow.

Some of those who question the claim that human activity is contributing to climate change have pointed out that the data show only an increase in global temperature. This, they argue, is not enough to prove that the change is anthropogenic. Scientists need to show that winds and moisture levels are also changing as a result of greenhouse gas emissions.

This is an entirely legitimate criticism, and it has now been answered.

Scientists at the Lawrence Livermore National Laboratory in California have shown that atmospheric water content over the oceans has increased since satellite measurements began in 1998. They have also searched through a database of of 22 different climate models, and correlated the model output with their satellite data. Some of the models include greenhouse gas emissions, some incorporate natural effects such as volcanic eruptions and variations in solar radiation, and others all, some or none of these.

The Lawrence Livermore study shows that model simulations which include greenhouse gas emissions most closely match the water vapour data, and the increase in moisture level is very close to that predicted from increased evaporation due to the temperature increase observed so far.

It will be interesting to see whether the sceptics can find any holes in this study.