In Scandinavia, a heatwave that currently occurs every twenty years might become so common that it occurs every five years. In southern Europe, heatwaves might become even more frequent. The change is thus different in different parts of the world.
Nor is the change in heatwaves proportional to the change in average temperatures. On a global scale, heatwaves are expected to double in frequency if the global average temperature rises by half a degree. Seemingly small limitations on the global temperature have a large effect on the frequency of heatwaves.
Heatwaves in a changed climate
It is hard to link individual weather events to climate change. Heatwaves occur when high pressure blocks – part of the weather’s random variations – build up.
However, the likelihood of heatwaves is increasing and the same weather conditions result in higher temperatures today than they did fifty years ago. These methods make it possible to demonstrate that some of the heatwaves in recent years probably would not have happened or would have been less extreme had it not been for global warming.