The Arctic tundra now emits more carbon dioxide and other greenhouse gases than it absorbs. Rising temperatures due to climate change have shifted the ecosystem鈥檚 effect on the planet 鈥� it has moved from helping to cool Earth to having a warming effect.
鈥淚t鈥檚 a really serious change,鈥� says at the National Snow and Ice Data Center in Colorado. 鈥淗uman-caused warming is now causing warming from nature. It is irreversible on a thousands-of-years timescale.鈥�
For millennia, Arctic ecosystems have taken up more CO2 than they emit. The loss of this natural carbon sink has happened because of rising temperatures鈥� complex effects on the carbon cycle. In some cases, warmer temperatures and higher levels of CO2 boost plant growth, causing them to take up more of the greenhouse gas. Higher temperatures also raise emissions by exacerbating wildfires and increasing decomposition in melting permafrost.
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at the Woodwell Climate Research Centre in Massachusetts and his colleagues estimated the average flux of carbon on land between 2000 and 2020, in both the Arctic boreal forest and the unforested tundra further north.
Looking at the Arctic as a whole, they found it remains a net sink of carbon. However, the Arctic tundra, which is warming faster than the boreal forests to the south, became a net source, emitting an average of about 60 million tonnes more carbon than it stored each year. That is not a massive amount of carbon on a global scale, says Rogers. 鈥淚t鈥檚 the transition that we鈥檙e concerned about.鈥�
During the 20 years studied, the tundra fluctuated from carbon sink to source, but the trend is clear, says team member at Northern Arizona University: 鈥淣o matter what happens this year or next year, it will continue to be a source.鈥�
Emissions are expected to rise with further warming. Since 2020, Schuur says he and his colleagues have seen record CO2 and methane emissions from other research sites in the Arctic, especially during the winter. 鈥淚n places where we鈥檙e hardly paying attention, we see records being set,鈥� he says.
The on changing emissions were part of a wider on the Arctic produced by the National Oceanic and Atmospheric Administration and presented on 10 December at a meeting of the American Geophysical Union in Washington DC. The report catalogued a slew of rapid signs of a shift in the Arctic, including a long-term warming trend, a loss of sea ice and declines in caribou populations.
While many of these changes aren鈥檛 reversible in the near term, the magnitude of the change is still affected by 鈥渆very fractional degree of warming鈥�, says Moon. 鈥淭he future does still depend on human action.鈥�
