The Earth’s ability to absorb nearly a third of man-made carbon emissions from plants could be halved over the next two decades at current warming rates, according to a new study in Science Advances by researchers from the University of Northern Arizona, the Udwell Center for Climate Research and the University of Waikato, New Zealand. Using data from more than two decades of measuring towers in every major biome around the world, the team identified a critical point above temperature above which plants’ ability to capture and store atmospheric carbon – a cumulative effect called “onshore carbon sink” “It’s declining as temperatures continue to rise.”
The terrestrial biosphere – the activity of terrestrial plants and soil microbes ̵
But as record temperatures continue to spread around the world, this may not continue; Researchers at NAU, Woodwell Climate and Waikato have found a temperature threshold above which carbon uptake in plants slows down and carbon release accelerates.
Lead author Catherine Duffy, a doctoral researcher at NAU, notes a sharp drop in photosynthesis above this temperature threshold in almost every biome in the world, even after eliminating other effects such as water and sunlight.
“The earth has a constantly growing fever, and like the human body, we know that every biological process has a number of temperatures at which it performs optimally and above which the function deteriorates,” Duffy said. “We wanted to ask how long can the plants last?”
This study is the first to detect a temperature threshold for photosynthesis from observations globally. While the temperature thresholds for photosynthesis and respiration have been studied in the laboratory, Fluxnet data provides a window into what the Earth’s ecosystems actually experience and how they react.
“We know that the temperature optimum for humans is about 37 degrees Celsius (98 degrees Fahrenheit), but we in the scientific community didn’t know what those optimums were for the Earth’s biosphere,” Duffy said.
She teamed up with researchers from Woodwell Climate and the University of Waikato, who recently developed a new approach to answering this question: Theory of Macromolecular Rate (MMRT). With its foundation in the principles of thermodynamics, MMRT allowed researchers to generate temperature curves for each major biome and globe.
The results were alarming.
The researchers found that the temperature “peaks” for carbon sequestration – 18 degrees C for the more common C3 plants and 28 degrees C for C4 plants – were already exceeded in nature, but they did not see a test of respiration temperature. This means that in many biomes, prolonged warming will reduce photosynthesis, while respiration increases exponentially, reversing the balance of ecosystems from the carbon sink to the carbon source and accelerating climate change.
“Different plant species differ in the details of their temperature reactions, but they all show a decrease in photosynthesis when it gets too hot,” said the NAU co-author. George Koch.
Currently, less than 10 percent of the Earth’s biosphere experiences temperatures above this photosynthetic maximum. But at current emission rates, up to half of the Earth’s biosphere could experience temperatures above that productivity threshold by the middle of the century – and some of the world’s most carbon-rich biomes, including tropical forests in the Amazon and Southeast Asia and the Taiga in Russia and Canada. will be among the first to reach this turning point.
“The most striking thing our analysis showed was that the temperature optimums for photosynthesis in all ecosystems were so low,” said Vic Arcus, a biologist at the University of Waikato and co-author of the study. “Combined with the increased respiration rate of the ecosystem through the temperatures we observe, our findings show that any increase in temperature above 18 degrees C is potentially harmful to the earth’s carbon sink. Without limiting warming to stay at or below the levels set out in the Paris Climate Agreement, the underground carbon sink will not continue to offset our emissions and save us time. “
Graphics by Victor O. Leshik, Center for Ecosystem Science and Society
Kate Petersen Center for Ecosystem Science and Society