Signs of Climate 'Doomsday' Clearly Visible in Leaves

The signs of Earth’s damage from climate change are becoming increasingly apparent. One ‘doomsday’ indicator of climate change due to global warming is now visible in the condition of leaves in the forest. Global warming is beginning to threaten the function of forests as the lungs of the planet. Trees play a crucial role in absorbing carbon dioxide through photosynthesis and producing oxygen for the atmosphere. If forest conditions continue to deteriorate, the impact will not only harm the environment but could also make it difficult for humans to breathe. Trees in forests are typically exposed to sunlight and absorb water through their roots. However, excessively high temperatures can become so extreme that they halt the photosynthesis process entirely. Research led by Gregory Goldsmith from Chapman University in California, along with his team, discovered that some parts of tropical forests are approaching a temperature threshold that disrupts photosynthesis. ‘The study shows that the leaves in tropical forests, at certain places and times, have already breached the critical temperature limit,’ Goldsmith said. Trees in tropical forests can carry out photosynthesis at temperatures up to 46.7 degrees Celsius. However, the researchers explained that the ability varies between species depending on the forest population, the number of leaves on a tree, and the canopy. To investigate this, a team from Northern Arizona University used data from NASA’s ECOSTRESS sensor, which measures the Earth’s surface temperature, to identify tropical forest leaves that were overheating to the point of being unable to photosynthesise. The data collected from satellite monitoring between 2018 and 2020 was then validated with surface sensors placed on the treetops of five forests in Brazil, Puerto Rico, Panama, and Australia. The analysis found that canopy temperatures in the forests peaked at 34 degrees Celsius during the dry season, although some leaves reached 40 degrees Celsius. A tiny fraction of leaves, 0.01 percent of the sample, exceeded the critical temperature of 46.7 degrees Celsius at least once during the dry season. ‘Although still rare, extreme temperatures can have a catastrophic impact on leaf physiology. It can be classified as a low-probability, high-impact event,’ the research report stated. According to a ScienceAlert report, trees close the pores on their leaves, called stomata, to conserve water when temperatures become too hot. This closure can potentially damage the leaf because it cannot ‘cool itself’ through the process of transpiration. During dry periods, when the soil hardens, the impact of extreme heat can be even more severe. ‘Believe it or not, we do not know much about why trees die,’ Goldsmith said. Scientific understanding of the effects of heat and drought, water and temperature, on plants remains very limited. The research team then used their data to run simulations to understand how tropical forests might respond to rising temperatures and increasingly frequent droughts. The simulation indicated that 1.4 percent of the upper forest canopy could stop photosynthesising in the near future as a result of global warming. If global warming exceeds 3.9 degrees Celsius, entire forests could become unable to cope. Leaves would dry out and trees across the forest would die one by one. However, the researchers stressed that these calculations are only probabilities. Severe impacts could occur at different temperatures. Therefore, it is crucial to reduce emissions and prevent deforestation to protect tropical forests.