As the Arctic warms, vast expanses of tundra have transformed into new forest growth. New research shows that forests are spreading across the Arctic tree line, where it is usually too cold and icy for trees to grow. By absorbing carbon, emitting water vapor that helps clouds form, and offsetting massive deforestation in the tropics, this forest expansion could help prevent further warming. In 2021, tree cover loss in northern polar regions was the highest on record. Boreal forest loss in Alaska, Russia, and Canada was up 30% largely due to wildfires.

Still, it’s unclear whether or not the benefits of the new growth will outweigh the costs of ice melt. Ice reflects sunlight, keeping the earth cool, whereas forested areas absorb it, which contributes to global warming and could potentially override their cooling effects.

Why This Matters

There’s no doubt that forests play an important role in reducing global warming. Forests across the world absorb about a third of the carbon emitted from burning fossil fuels and keep the earth about a half-degree Celsius cooler on average. That said, with carbon offsets becoming an increasingly popular way for corporations to reach their net-zero goals, more and more forests are being viewed as a cure-all for climate change rather than the complex ecosystems they are. Many carbon offset projects fail to consider how droughts or wildfires keep forests from acting as carbon sinks. A 2019 report from ProPublica exposed how offsets have not actually reduced greenhouse gas emissions as intended.

The study of these new Arctic forests emphasizes the complexity of forests’ relationship to climate change. "Forests are not just carbon sponges,” environmental scientist Deborah Lawrence of the University of Virginia told Science, even though their other effects are "not adequately captured by current carbon-centric metrics.”

Missing the Forest for the Trees

The world’s forests are in danger. Since 2000, its lost 11% of its tree cover. In the last two decades, climate change and deforestation have reduced the stability and resilience of the Amazon rainforest by 75%, causing it to release more carbon than it is absorbing. According to a study in Nature Sustainability, tropical forest carbon loss doubled over the past 20 years and is continuing on that trend.

But polar ice caps are also important in mitigating climate change, providing benefits that forests cannot. Moreover, the ability of a forest to act as a carbon sink depends on latitude, altitude, how fast the trees grow, and the age of the forest. In colder climates, where trees grow more slowly, they exhibit a reduced ability to capture carbon.

Chris Williams, a geographer at Clark University, told Science: I really worry that we could be placing too much emphasis on forests as a climate solution, when what we really need is deep decarbonization of society.”