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"Browning that raises the eyebrows. Credit: Rachael Treharne, Author Provided
In recent years, Arctic scientists have made a startling discovery: vast areas of the Arctic are turning brown. This is partly due to extreme events related to winter conditions, such as brief and short periods of heat. These events occur when the climate warms up, which occurs twice as fast in the Arctic than in the rest of the planet. Extreme events therefore occur more and more often, with more and more serious effects, including extensive damage and the death of Arctic plants.
This "browning" of plant communities has occurred over thousands of square kilometers or more. However, until recently, we knew very little what this could mean for the balance between carbon uptake and release in Arctic ecosystems. Since the Arctic stores twice as much carbon as the atmosphere, it is an urgent concern.
Our study has now shown that extreme weather events can significantly reduce the ability of Arctic ecosystems to absorb carbon, which has implications for whether the Arctic will contribute to the fight against climate change or climate change. to his acceleration.
The cost of carbon from extreme weather
To understand the impact of extreme events on arctic moors, we visited the Lofoten Islands in northern Norway, where subarctic coastal plant communities act as an indicator of future climate change in the far north. showing the effects of warming in the region.
We have seen the effects of two extreme weather events in winter. Firstly, the "frost drought" caused a significant dieback of the plants. Frost dryness occurs when the layer of insulating snow that usually protects plants from the harsh Arctic winter is melted, usually because of unusually high winter temperatures. If the plants remain exposed long enough to cold and wind, they continually lose water and are unable to replace it with frozen soil. Finally, they succumb to drought.
Dead and brown vegetation on a heath in Norway. Credit: Rachael Treharne, Author Provided
The second event was "extreme winter warming" – a sudden explosion of high temperatures in the winter melting snow and causing evergreens to get ready for spring by losing their cold tolerance. When the warm period is over, the return of cold temperatures usually kills the plant. In this case, however, we found something unexpected. The heathland plants had survived this extreme warming event in winter, but showed signs of severe stress, visible in the form of a deep dark red color and persistent in the shoots and leaves.
We measured the amount of carbon dioxide absorbed and released by plants in three types of vegetation: damaged heathland (where the dominant evergreen species had been killed by frost drought), stressed moors and healthy moors, and which had escaped the effects of vegetation. an extreme event. This was done in three measurement periods throughout the growing season.
We found that these extreme winter conditions reduced the amount of carbon absorbed by heathland ecosystems by up to 50% throughout the growing season. There is a considerable reduction in the ability of an extensive Arctic ecosystem to remove carbon from the atmosphere.
Surprisingly, this was the case both in the damaged moors, where much of the vegetation had been destroyed, and in the stressed moors. Although the processes behind this change have been different in each type of heath, this clearly shows that we must take into account the role of plant stress in limiting carbon uptake by plants in order to fully appreciate the consequences of extreme weather events.
A dark red pigmentation indicates that this plant is stressed by the unpredictable climate. Credit: Rachael Treharne, Author Provided
The big north brown
What does this mean for the Arctic? We now know that extreme weather events could significantly reduce the ability of Arctic ecosystems to absorb carbon and combat climate change.
This is all the more worrying as the effects of browning strongly contrast with those of a better understanding of Arctic ecosystems to climate change: "greening in the Arctic" or the tendency of plants to become higher and more productive as the Arctic summers heat up.
At the present time, many climate models assume arbitrary levels of greening in the Arctic and therefore Arctic ecosystems will use more carbon in the future, which will slow down climate change. The magnitude of browning observed in recent years, combined with the negative effects on carbon absorption reported here, suggests that the reality could be more complex, challenging our understanding of the role of the Arctic in the climate of the Earth.
What does this mean for us? The impact of extreme weather in the Arctic has global consequences. It is clear that our current efforts to combat climate change are dangerously inadequate, but ambitious measures could now reduce the temperature predicted for global warming by 7 ° C. This is essential to minimize the impacts of climate change in Arctic ecosystems and around the world.
Instruments for measuring the absorption and release of carbon at the test site. Credit: Rachael Treharne, Author Provided
Explore further:
More persistent weather conditions in the United States related to Arctic warming
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