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Welcome to the Great Green North

Space satellites show Arctic awash in grass and flowers

JANE GEORGE

It’s true: the Arctic is more green in summer — although this greening may be a sign that global warming will hit the world more quickly and harder than previously forecast.

Anyone looking around last summer in Iqaluit saw an amazing carpet of soft green grasses and thousands of colourful flowers.

This sight is even visible from space, where satellites circling the polar regions have picked up an increasing amount of vegetation in the higher latitudes during the summer.

A new study of these satellite images confirms the tundra is becoming, on average, greener from one year to the next. Analyses of a 22-year record of satellite observations show that for about 10 years the high latitudes have been greening in response to the warmer temperatures — that is, tundra vegetation is starting to grow earlier in the spring and continuing to grow more intensely during the summer

All land surfaces above 50° N, excluding the glaciers of Greenland, were included in a study in the current issue of Earth Interactions.

“Greening is, in fact, happening in the tundra areas — they are greener in the summer than they have ever been before,” said Andrew Bunn, a scientist at the Woods Hole Research Centre in Massachusetts, and one of the authors of this study.

But this same growth and greening isn’t happening over big chunks of boreal forest to the south.

Even after masking out the impact from forest fires, Bunn said he was surprised to see sub-Arctic boreal forests are not thriving.

During the first 10 years of warming temperatures, boreal forests grew vigorously, but, from 1994 to 2002, growth in many places slowed as temperatures climbed and the forest dried out.

“We can’t really decide why it’s happening,” Bunn said. “We find more greenness in the spring, but this seems to be canceling out in the late part of the summer when we find browning.”

This suggests vegetation is responding to climate change in unexpected ways and the ability of boreal forests to capture and store the greenhouse gas carbon dioxide in a warmer world will not live up to previous expectations.

“It’s suggesting that the simple idea that we just turn up the heat a little bit, and the boreal forests will be able to store more carbon into the ground doesn’t work,” Bunn said.

Carbon dioxide molecules now make up about 380 parts of every million parts of air. That’s well above other levels from the past 400,000 years, all of which topped out at less than 300 ppm, according to analysis of air bubbles in ancient ice cores.

If these forests aren’t storing more carbon dioxide in their soil and trunks and the greening tundra regions are releasing more carbon dioxide into the atmosphere from the warmer soil, global warming may speed up and intensify.

“In terms of managing the atmosphere we’d probably like the situation to be reversed,” Bunn said. “We’d like the tundra not to be releasing carbon [dioxide] and we’d like the forests to be storing carbon [dioxide].”

A little over 30 percent of the world’s forests are in the Far North, with boreal forests covering 17 per cent of the world’s land surface area, so northern forests are a big storage area for carbon dioxide.

But the sub-Arctic may simply be getting “too hot for trees,” he said, which means scientists will have to re-think how the world will handle increasing emissions of carbon dioxide.

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