Tropical Rainforests Could Get Too Hot For Photosynthesis, Scientists Warn – Slashdot

Using data collected from the International Space Station (ISS), scientists found that a small yet growing percentage of tree leaves in tropical forests are approaching the maximum temperature threshold for leaves to photosynthesize,” reports Live Science. If this trend continues, it could spell disaster for Earth’s climate systems and biodiversity. The findings have been published in the journal Nature. From the report: The average critical temperature beyond which photosynthetic machinery in tropical trees begins to fail is 116 degrees Fahrenheit (46.7 degrees Celsius). Currently, only 0.01 % of all leaves surpass this critical temperature every year. But scientists warn that air temperature rises of 7.2 F (4 C) could push trees in tropical forests beyond a tipping point and into mass death. “It’s concerning from our perspective that you see nonlinear trends. So you heat the air by, let’s say, 2, 3 degrees Celsius [3.6 to 5.4 F], and the actual upper temperature of these leaves goes up by 8 degrees [Celsius; 14.4 F],” Christopher Doughty, an associate professor of ecoinformatics at Northern Arizona University, said during a press conference on Monday (Aug. 21). “Even though a small percentage of leaves are currently doing this, our best guess is that a 4 degrees Celsius increase in temperature could cause some serious issues for certain tropical forests.” […]

Plugging these peak temperatures into a mathematical model, the scientists found that an average 7 F (3.9 C) increase in the air temperature surrounding the leaves caused those most exposed to the heat to have their water-carrying stomata closed off by the tree, leading to their deaths. This triggered a cascade effect, increasing the temperature around the remaining leaves and potentially killing them, their branches and the trees in turn. “If you have 10% of the leaves dying, the whole branch is going to be warmer because a critical part of that branch can no longer cool the broader branch. Likewise you can make that assumption across the whole forest when a tree dies,” Doughty said.