CLIMATE change could be responsible for reindeer deaths. In a lethal chain of events, warming causes more rain to fall onto snow-laden pastures, forming ice crusts over the soil surface that leave the animals with nothing to eat.
Researchers had already noticed that winter rainfall seems to be followed by a lot of reindeer deaths. They thought this had to do with ice forming at the soil surface, but no one knew what weather conditions make rainfall likely, or why the ice forms.
To find out, Jaakko Putkonen and Gerard Roe from the University of Washington in Seattle analysed soil temperatures and meteorological data from the Arctic island of Spitsbergen. From this they worked out that the rainwater seeps through the snow to the ground, where it freezes as heat is lost to the colder permafrost beneath. Reindeer and other ungulates such as caribou and elk can鈥檛 break through the ice to feed, says Putkonen, and in extreme cases they starve. Calves are particularly vulnerable.
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The researchers will report in Geophysical Research Letters that the likelihood of rain falling on snow (ROS) depends on the atmospheric circulation pattern known as the North Atlantic Oscillation. When the NAO is in its 鈥渉igh phase鈥�, strong winds bring storms and warm air from the south, causing rain to fall instead of snow. 鈥淚n a normal year there are not more than two days of ROS in Spitsbergen,鈥� says Roe. 鈥淏ut during a high-phase year there may be as many as nine days.鈥� Just a few days of ROS are enough to cause icing that lasts the whole winter, he adds.
As well as Spitsbergen, animals in other permafrost areas such as Scandinavia, Siberia and Alaska are affected by the ice, which can last for long periods. And the researchers found that things are likely to get worse over the next century as global temperatures rise. 鈥淏y 2080 ROS is likely to affect 40 per cent more land than it does at present, squeezing the reindeer into an ever smaller area,鈥� says Roe.
