Greening Tundra Shows Arctic Heat

Posted on Mar 13, 2013

madpai (CC BY 2.0)

By Tim Radford, Climate News Network

This piece first appeared at Climate News Network.

LONDON—The Arctic is on the move. The North Pole is in the same place, but Arctic conditions have begun to shift. A study of 30 years of satellite data confirms that the difference in temperatures between the seasons has diminished.

Conditions now have shifted the equivalent of four or five degrees of latitude southward. At the same time, vegetation has moved north, colonizing the thawing permafrost.

A team of 21 scientists from 17 institutions in seven nations reports in Nature Climate Change that as the cover of snow and ice has diminished and retreated in the Arctic Circle, the temperatures have begun to increase – at differing rates – during the four seasons. Although conditions differ from region to region, overall the growing season is beginning earlier, and the autumn freeze is starting later.

Conditions in northern latitudes now increasingly resemble those found several hundred miles further south 30 years ago. One of the authors, Bruce Forbes of the University of Lapland in Finland, told the Climate News Network that in his own research region of north-west Siberia “we are seeing more frequent and longer-lasting high pressure systems. In winter, the snow cover comes later, is deeper on average than in the 1960s, but is melting out earlier in spring.”

Climate is a complicated business, and there is always legitimate room for argument about the validity of one selected set of measurements, a potential bias in the observations, or the reliability of comparison data collected two generations earlier.

But vegetables can’t be fooled. Plants grow where they can. If deciduous shrubs are growing taller, and colonizing sites ever further north, then conditions must be getting warmer, and staying warmer.

Winners – and losers

Professor Forbes says that indigenous reindeer herders report that alder and willow, normally stunted by the polar winter, are growing taller: his own research team has confirmed this with dendrochronology, the science of tree ring measurement.

“In a few decades, if the current trends continue, much more of the existing low shrub tundra will start to resemble woodlands as the shrubs become tree-sized”, he says.

This enhanced warming over a longer ground-thaw season has changed the landscape: it has, says Compton Tucker of the Goddard Space Flight Center in the US, “created during the past 30 years large patches of vigorously productive vegetation, totaling more than a third of the northern landscape – over nine million km2, which is roughly about the area of the USA -  resembling the vegetation that occurs further to the south.”

This warming of the high latitudes is not necessarily good news for all plants. As the tundra turns green at an accelerating rate, the growth of the boreal forests – those mighty stands of conifer species that cover northern Canada and northern Eurasia and enclose the Arctic Circle – may even be decelerating.

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