As hill walkers and mountain climbers know so well, the higher you climb, the cooler the weather. The same happens to plants and animals that are migrating up mountains in search of cooler temperatures as climate change makes life too warm for them lower down the slopes. A recent study of forest plants in Western Europe shows that on average most of them have climbed nearly 30m (98ft) each decade for the past century as they seek out colder refuges. Eventually many plants will run out of slopes to climb, and then they will face extinction or somehow have to move further north.

Something remarkably similar is happening in the sea: fish are diving deeper to seek cooler temperatures. A new study has revealed that over the last quarter of a century North Sea fish have dived deeper by an average of 9m (30ft), and some species have sunk far deeper than that.

The problem they face is similar to the mountain plants. Sooner or later the fish will run out of deep sea, especially in the southern parts of the North Sea, which are quite shallow. The only alternative then is for them to seek out colder waters further north. But then they will run into problems of different habitats they may not be able to adjust to.