of changes to ecosystems that are occurring in response to changing climates around the world. But the rate at which changes are occurring in the high Arctic far outstrips that seen elsewhere in the Northern Hemisphere.

"We suddenly realized that the trends are dramatically stronger than elsewhere," says Toke Høye of the University of Aarhus, Denmark, who led the research. Previous worldwide studies of animals and plants have suggested that, globally, the beginning of spring is advancing by around five days per decade.

But in the frozen valleys of Zackenberg, northeastern Greenland, the rate of change is almost triple the world average, Høye's team has discovered. "This is the first study of its kind in the high Arctic," he says. It's quite a surprise to see such a huge difference."

Spring forwards

Høye and his colleagues monitored the timings of 66 separate biological indicators of spring-time, including the emergence of a wide range of insects, egg-laying in birds, and the appearance of flowers. Although the average advance is 14.5 days, some birds are now laying their eggs more than a month earlier than in 1996, the researchers report in Current Biology1.

We suddenly realized that the trends are dramatically stronger than elsewhere.

Toke Høye, University of Aarhus

During that decade, average June temperatures at Zackenberg have climbed by 1.1 ºC — more than double the global average. And that has an impact on the timing of the annual snowmelt, which in turn affects the wildlife. "There's a very conspicuous pattern in which spring is initiated by snowmelt — that's when biological activity starts," Høye explains. As warmer temperatures cause snow to melt earlier, plants and animals are flowering and reproducing earlier too.

Overall, the effect could potentially extend Greenland's short, cold summer by as much as 25%, Høye predicts. Currently, there are just three or four months between snowmelt and the onset of the winter freeze.

Initially, this may have a positive effect on extreme northerly ecosystems, as the longer summer allows greater productivity. But ultimately, warmer summers could lead to extinctions, as temperatures drive cold-loving species further north, Høye says. "There are still 500 kilometres from the study site to the northern tip of Greenland, but eventually there will be nowhere to go," he says. What's more, as temperatures rise, more southerly species could migrate north to colonize the area.

It is difficult to say whether the trend will continue as strongly as it has since 1996, Høye says. Although temperatures are set to keep rising, this may bring an increase in precipitation, which will largely come as snow. This could in turn help to delay the completion of spring melt and curtail the advance of spring-time in the snowiest areas, which have so far shown the greatest vulnerability to change.

"It's tricky to predict what this all means for these different areas," Høye admits. "It's really up in the air."