June 5, 2012
Warming Arctic Climate Turns Shrubs To Forests
Plants and shrubs in the Arctic tundra have turned into small trees in recent decades due to the warming Arctic climate. If the trend continues on a wider scale, it would significantly accelerate global warming, said scientists from Finland and Oxford University in a new study published in the journal Nature Climate Change.
The researchers investigated an area of 100,000 square kilometers from western Siberia to Finland known as the northwestern Eurasian tundra. Surveys of the area´s vegetation, using data from satellite imaging, fieldwork, and expert observations from indigenous reindeer herders, revealed that willow (Salix) and alder (Alnus) plants have grown into trees over 6 feet tall in 8 to 15 percent of the area during the last 30-40 years, the researchers said.
"It's a big surprise that these plants are reacting in this way," said Marc Macias-Fauria of Oxford University, lead author of the research.
Experts had previously believed such colonization would take centuries, he added. Indeed, previous studies suggested that advancement of the forest into the Arctic tundra could raise Arctic temperatures by an extra 1.8 to 3.6 degrees Fahrenheit (1-2 degrees Celsius) by the end of the 21st Century.
"But what we've found is that the shrubs that are already there are transforming into trees in just a few decades,” Macias-Fauria said.
Temperatures in the Arctic are warming at nearly twice the rate as temperatures in the rest of the world, the scientists said.
As reflective snow and ice recede, soil or water is exposed, presenting darker colors that absorb more of the sun's heat.
The same phenomenon occurs when trees are tall enough to rise above the snowfall, exhibiting dark surfaces that absorb sunlight.
This growth from shrubs to forest is significant as it changes the albedo effect — the amount of sunlight reflected by the surface of the Earth, said Professor Bruce Forbes of the Arctic Centre, University of Lapland, co-author of the study.
The increased absorption of the Sun's radiation, combined with microclimates created by forested areas, accelerates global warming, making an already-warming climate even more so, he said.
"The speed and magnitude of the observed change is far greater than we expected.”
While additional Arctic warming may generate new oil and gas development in the area, and will likely attract herds of reindeer that feed on willow shrubs, a warming planet will also cause severe droughts and flooding in other places throughout the world, scientists say.
Macias-Fauria acknowledged that the area researched in the study is only a small part of the massive Arctic tundra, and an area that is already warmer than the most of the Arctic, likely due to the impact of warm air from the Gulf Stream.
"However, this area does seem to be a bellwether for the rest of the region, it can show us what is likely to happen to the rest of the Arctic in the near future if these warming trends continue."
The research was published online June 3 in the journal Nature Climate Change. The full report can be viewed here.