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“Yes, we can all plant trees… and if we still keep emitting carbon dioxide like crazy, we will not have solved anything – we just bought a little bit of time,” he said.

“If we want to control climate change, there is really only one answer… we have to cut emissions,” he added by phone.

Environmentalists say protecting existing forests and restoring damaged ones prevents flooding, stores planet-warming carbon, limits climate change and protects biodiversity.

But the tropics lost 12 million hectares of tree cover in 2018, the fourth-highest annual loss since records began in 2001, according to monitoring service Global Forest Watch.

Of greatest concern, it said, was the disappearance of 3.6 million hectares of old-growth rainforest, an area the size of Belgium, much due to fires, land-clearing for farms and mining.

Crowther Lab scientists this year published what they said was the first study of how many trees the world could support, where they could be grown, and how much carbon they could store.

The study analyzed the maximum amount of carbon that could be captured if all available degraded forest areas not used by humans were replanted and allowed to mature.

But researchers at the University of Bonn and World Agroforestry questioned its findings in their letter.

The Crowther Lab’s classification of many “high-potential” regions for tree planting was based on average temperatures and did not take into account the highest and lowest temperatures experienced in places like the tundra and Africa’s savannas, said Luedeling.