Satellite sensing reveals tropical forests are much closer to a major tipping point than previously thought, but are only likely to pass it in worst-case warming scenarios
International Space Station from 2018 to 2020, Doughty and his colleagues found that around 0.01 per cent of leaves in the canopies of rainforests around the world are already reaching this threshold.
To confirm this, the researchers did a number of ground-based studies around the world, including placing temperature sensors on individual leaves in the upper canopy of rainforests. “This is incredibly challenging,” says Slot. “You come back, and a storm has ripped the sensors off or ants have eaten the tape.”
They then created a simple model based on these findings and on experiments involving warming plants. They concluded that the proportion of leaves affected will increase as local temperatures increase, rising more rapidly after reaching a tipping point between 2 and 8°C of local warming, mostly likely at 4°C .
There are a number of reasons why the rise might accelerate, says Doughty. For instance, the pores of leaves, called stomata, will closeto prevent water loss. Without the cooling effect of evaporation through the stomata, the leaves warm rapidly. In addition, once the most heat-exposed leaves start dying, others that were previously sheltered become exposed and die as well.Continuing deforestation will make it more likely that local temperatures could increase to levels where lots of leaves start exceeding the limit, says Doughty. “Where you have fragmentation of forests, the existing forests get quite a bit warmer,” he says.
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