What is the maximum temperature before the rainforest dies? According to scientists

Heat kills any living organism. What varies is the maximum temperature and time an organism can tolerate before dying. Since the chemical reactions that keep an organism alive depend on molecules that lose their structure and stop working at high temperatures, this number varies slightly.

Even thermophilic organisms that live near underwater volcanoes find it difficult to withstand temperatures above 70 degrees Celsius. On the surface of the planet, few organisms can survive at 50 degrees. Mammals can tolerate high temperatures because they have a cooling system, sweating, which keeps their internal body temperature close to 37 degrees. If it exceeds 42.3 degrees, our lives are at risk.

In 1864, a scientist named Sachs demonstrated that plant leaves die when exposed to temperatures close to 50 degrees Celsius. Today we know that it only takes a few seconds at 46.3°C for the machinery responsible for photosynthesis in plants to be irreversibly damaged.

Despite rapid global warming, atmospheric temperatures of 46.3°C rarely occur outside desert regions. But as temperature fluctuations increase (for example, the maximum El Niño temperature in 2015 was 1.5°C higher than in 1997), it is not impossible to imagine that these temperatures could be reached for a few hours a day. In the tropics, this is enough to kill a forest.

With this question in mind, scientists decided to once again check the maximum air temperature in the tropical forest canopy throughout the year. But now with a new way. The International Space Station has a camera capable of measuring the temperature on the planet’s surface. The system is called Ecostress.

In a first experiment, measurements obtained by this system were calibrated using equipment placed in the forest canopy. This was done by comparing direct measurements made with thermometers with those made by Ecostress. Once this was done, the scientists were able to accurately measure the temperature in the forest canopy in different regions of the planet throughout the year.

The results showed that in tropical forests, only 0.01% of the time (about 50 minutes per year) the tree canopy temperature reaches 46.3°C. This is not enough to affect the photosynthesis system in forests.

But in experimental fields in Brazil, Costa Rica and Australia, where the temperature in the tree canopy is artificially increased by 2 to 4 degrees Celsius to study the effect of global warming, the temperature in the leaves reached a limit of 46.3. °C for 1.3% of the time, which is already affecting forests. In the coming years, when this experiment is over, we will know whether trees exposed to these temperatures will survive.

The question then is how much the planet can warm before a significant portion of tropical forests die from rising temperatures from time to time. Calculations indicate that tropical forests could withstand a global warming of more than 3.9 degrees Celsius before collapsing. We are still far from this value, but it is good to remember that the Earth’s temperature is currently warming at 0.5 degrees Celsius per decade.

In the most pessimistic CO2 emission scenarios (so-called RCP 6 and 8.5 models) a temperature increase of 4°C could occur by 2080. If we do not control CO2 emissions, children born today They may suffer forests disappearing before they reach 60 years of age. Not because of deforestation, but because of the heat.

more information: Tropical forests are approaching critical temperature thresholds. Nature 2023