The Guardian

Warmer winters may seem good for Arctic animals. In fact they can be deadly

 A Sami woman observes the movement of reindeer during selection and calf labelling near the village of Dikanaess in northern SwedenA Sami woman observes the movement of reindeer during selection and calf labelling near the village of Dikanaess in northern Sweden. Photograph: Jonathan Nackstrand/AFP/Getty Images

Not even donkeys get a worse deal in popular culture than the reindeer. Rabbits, mice, cats and even bears all have their distorted images in cartoons, but all of them show some sympathetic qualities of intelligence or kindness. Only the reindeer is forced in songs and cartoons to live down to the mangy and dispirited creatures chained up and sweating in rainy British theme parks. Even rats make cartoon heroes. Only reindeer are always caricatured as drunken, stupid and quarrelsome beasts of burden.

In real life the partnership of the reindeer with the Sami peoples of northern Scandinavia is one of the great triumphs of domestication, enabling humans to build a culture in a landscape so cold, bare and hostile that without the reindeer it would have been impossible to live there at all. The Sami and their reindeer live far to the north of the Inuit of North America, and have for hundreds of years been pushed further into the wilderness by settled farmers encroaching from the south. Until recent times the reindeer supplied almost all the technology their herders needed: bone needles, and thread made of sinew to sew together warm clothes from skin.

Together the herds and their herders travel hundreds of miles every year, in search of food, minimal warmth, and escape from mosquitoes. But it is important that the warmth not be too great. One of the greatest catastrophes that can befall a herd of reindeer is a warm spell in spring, where warmth is defined as anything above freezing. If in the daytime rain falls instead of snow, it will freeze into ice when the weather returns to normal and, while reindeer can dig through deep dry snow to reach the lichen on which they live, they cannot break through a crust of ice. The food remains as inaccessible as if it were behind glass. This is a natural disaster that can wipe out an entire population – about 60,000 reindeer died in one Siberian incident in 2013 – and even those animals that survive will be greatly weakened.

Now there is evidence that this effect is attacking the wild reindeer population of the Svalbard archipelago as a result of climate change. That has progressed at an astonishing rate. The mean temperature in January has risen by nearly 10C in the last 26 years. In July, over the same period, it has only risen by a 1.5C, but both changes have had profound effects. The slightly warmer summers have crossed an important threshold for plant life, so that there is now a great deal more nourishment available in the fat times. But this seems to be outweighed by the loss of food caused by wintertime warming.

It might seem that a warmer world would be unambiguous good news for the plant and animal life of the arctic. Indeed, there are now more reindeer in the population studied than there were 20 years ago. But the problem of rain refreezing over plants turns out to be more important than all the gains from plants growing larger in a longer summer. The average weight of reindeer on the island has shrunk by 12% over the last 16 years as the island has grown steadily less cold.

Warm summers mean more adults, but the warm, or less cold, winters mean malnourished mothers that have fewer successful pregnancies and weaker babies if they are carried to term. The disruptions caused by climate change will be greater than we can easily imagine, and much less predictable.