As climate warms, scientists in Greenland warn the small Arctic shrubs could stop absorbing carbon and start emitting it
The Arctic tundra could become a source of CO2 as the planet warms and the permafrost melts, say scientists from northeast Greenland.
The small mosses and shrubs, the only plants capable of growing on the Arcticâ€™s permanently frozen soil and which cover vast areas of the Northern Hemisphere, could flip from being a carbon sink to a carbon source as temperatures rise.
The scientists from Aarhus University, who undertook research at the Zackenberg Research Centre, compared the amount of CO2 released by the plants as they respire to the amount that they store due to photosynthesis.
“We can see that the annual release of CO2 from living organisms increases linearly as the temperature increases,â€ť explains researcher Marcus Lund.
â€śHowever, it seems that the ability of the photosynthesis to assimilate carbon stops increasing when the temperature in July rises above approximately 7C, which has occurred several times in past years.
â€śThis means that the tundra may become a CO2 source if the current strong climate warming continues as expected.”
The recent IPCC fifth assessment report confirms with high confidence that, over the last 20 years, the ice in the Arctic has suffered a severe decline.
It says: â€śthe Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extentâ€ť.
Lund emphasises that methane, a gas whose warming effect is 20-25 times stronger than CO2, will remain the Arcticâ€™s primary contributor to the Earthâ€™s greenhouse gas budget.
In 2007, scientists at the same research station found that, in autumn, when the surface of the tundra freezes and ice is formed, large quantities of methane are released.
The researchers are still trying to find out exactly how and when this methane is formed, but Lund says that it is difficult to collect adequate measurements in the remote Arctic region.
“It’s a problem in the Arctic that we don’t perform measurements at enough locations,â€ť he says.
â€śThe variation between locations is substantial both for CO2 and not least for methane. In Greenland, we measure near Nuuk and in Zackenberg, where we collect measurements from a relatively dry heath and from a moist fen area.â€ť