Context:

• Permafrost in the coldest northern Arctic will thaw enough to become a permanent source of carbon to the atmosphere this century, with the peak transition occurring in 40 to 60 years, a NASA study warns. The region was formerly thought to be at least temporarily shielded from global warming by its extreme environment.

Permafrost:

• Permafrost is soil that has remained frozen for years or centuries under topsoil.
• It contains carbon-rich organic material, such as leaves, that froze without decaying.
• The study published in PNAS found that warmer, more southerly permafrost regions will not become a carbon source until the end of the 22nd century, even though they are thawing now. That is because other changing Arctic processes will counter the effect of thawing soil in these regions, researchers said.
• The finding that the colder region would transition sooner than the warmer one came as a surprise, according to Parazoo. “Permafrost in southern Alaska and southern Siberia is already thawing, so it is obviously more vulnerable,” he said.
• “Some of the very cold, stable permafrost in the highest latitudes in Alaska and Siberia appeared to be sheltered from extreme climate change, and we did not expect much impact over the next couple hundred years.”

Simulation studies

• As rising Arctic air temperatures cause permafrost to thaw, the organic material decomposes and releases its carbon to the atmosphere in the form of the greenhouse gases carbon dioxide and methane.
• Plants remove carbon dioxide from the air during photosynthesis, so increased plant growth means less carbon in the atmosphere. According to the model, as the southern Arctic grows warmer, increased photosynthesis will balance increased permafrost emissions until the late 2100s.

Source:TH