Global warming is bringing leafy tropical canopies close to temperatures where they can no longer convert sunlight and CO ₂ for energy, which, according to a study released Thursday, threatens complete collapse if the thermometer continues to rise. Study published in Nature reported that a small percentage of upper canopy leaves had already crossed this threshold, reaching temperatures high enough – above 47 degrees Celsius – to prevent photosynthesis. Currently, some leaves exceed such critical temperatures only 0.01 percent of the time, but the surges could quickly increase because leaves heat up faster than the air, the researchers said. "You warm the air by two to three degrees and the actual upper temperature "These leaves will rise by eight degrees," lead author Christopher Doughty of Northern Arizona told reporters. If the average surface temperature of the tropical forest warms by 4°C above current levels, which is generally considered worst case scenario , "we predict possible complete leaf death," he said. (Linnea Pedersen, Marlowe HOOD)