Trees, natural carbon sponges, help keep heat-trapping carbon dioxide out of the atmosphere. But insect and human threats are taking a heavy toll on them.
Experts are scrambling to understand the situation, and to predict how serious it may become.
Scientists say the future habitability of the Earth might well depend on the answer. For, while a majority of the world’s people now live in cities, they depend more than ever on forests, in a way that few of them understand.
Scientists have figured out — with the precise numbers deduced only recently — that forests have been absorbing more than a quarter of the carbon dioxide that people are putting into the air by burning fossil fuels and other activities. It is an amount so large that trees are effectively absorbing the emissions from all the world’s cars and trucks.