Even modest global warming threatens Northern Hemisphere forests

(Paris) Even a moderate change in temperature and precipitation could harm the forests of the northern hemisphere, the rich biodiversity they shelter and their capacity to store carbon, according to a study published in Nature.

The boreal forests, which cover large swathes of Russia, Alaska and Canada, are important carbon sinks, but they are threatened by increasingly frequent fires and invasive species favored by global warming .

To find out how higher temperatures and less rain can affect the most common species in these forests, researchers conducted a five-year experiment, the results of which were published on Wednesday in the scientific journal Nature.

From 2012 to 2016, they grew 4,600 specimens of nine tree species, including spruce, fir and pine, in northeast Minnesota. Using underground cables and infrared lamps, these young shoots were heated to two different temperatures, 1.6°C above room temperature and 3.1°C above.

Tarps were positioned at half of the sites to retain rainwater and mimic the changes in rainfall that climate change is expected to cause.

Even at 1.6°C, tree growth was impaired by increased mortality and reduced development. Warming, alone or combined with less rain, increased the mortality of young trees among the nine varieties studied.

The Paris Agreement of 2015 aims to limit global warming to well below 2°C compared to the pre-industrial period, even 1.5°C, but the current commitments of governments lead instead to a warming of 2, 7°C over the century.

Previous studies have shown that climate change could have both positive and negative effects on boreal forests, such as a longer growing season in the far north.

The growth of maples and oaks, rare today in boreal forests, was thus accelerated at 1.6°C, while conifers fared less well.

Rising CO levels₂ in the atmosphere could have “modest positive effects” on some species, the study’s lead author, Peter Reich, told AFP, but plants could be saturated with CO₂ and more fires are leading to it being released back into the atmosphere, he warned.