Forests and other land ecosystems today account for 30 per cent of human CO2 pollution, but global warming could transform these natural ‘sinks’ into ‘sources’. carbon within a few decades, opens up another daunting face in the fight against climate change, scary researchers have said.
Climate skeptics often describe CO2 as a “plant food”, suggesting that increased greenhouse gas emissions will be offset by a dramatic increase in plant growth.
But the new study shows that beyond a certain temperature level – which varies by region and species – the ability of plants to absorb CO2 is declining.
Under current greenhouse gas emission trends, plants across half of the world’s terrestrial ecosystem could release carbon into the atmosphere faster than they captured it by the end of the century, he said. researchers this week there Advances in science.
Ecosystems that store most of the CO2 – especially tropical and boreal forests – could lose more than 45 percent of their capacity as carbon sponges by mid-century, a team led by Katharyn Duffy has found from the University of Northern Arizona.
“Expected higher temperatures associated with elevated CO2 could reduce ground carbon uptake,” the study said, based not on modeling but on data collected over a 25-year period.
If you don’t take this into account, the potential role of Earth’s vegetation in reducing global warming becomes “too much of an overview”, the researchers warned.
“The temperature point of the earthworm is not at the end of the century or beyond, but within the next 20 to 30 years.”
A key way to understand how this can happen is the difference between photosynthesis and mitigation, two chemical processes necessary for plant life that respond differently to rising temperatures. .
Extracting energy from sunlight, plants absorb carbon dioxide through their leaves and water from the soil, making sugar to stimulate growth and oxygen, which is released into the air. .
This is a photo-synthesis, which can only occur in daylight.
In contrast, the transfer of energy to cells through emission – with CO2 inhibited as a result of waste – occurs around the clock.
Waste points
To determine if temperatures are higher than land-based ecosystems would start to absorb less CO2, Duffy and her team analyzed records from a global observation network, called FLUXNET, spanning 1991 to 2015.
FLUXNET largely monitors CO2 movement between ecosystems and the atmosphere.
They found that global photo-synthesis occurs at a given temperature, depending on the type of plant, and then decays thereafter.
Respiratory levels, however, rise across all types of ecosystems without appearing to reach a maximum.
“At higher temperatures, respiratory rates continue to rise relative to declining levels of photosynthesis,” the study found.
If carbon pollution continues unabated, this split will see CO2 fall by half as early as 2040.
“We are rapidly entering temperature regimes where biosphere productivity declines sharply, raising the question of the future viability of the land sink,” the researchers concluded.
The findings also raise questions about the integrity of many national commitments under the Paris Agreement – known as nationally proven grants, or NDCs – to reduce greenhouse gases.
“These are heavily dependent on carbon sequestration to meet commitments,” the authors point out.
The study notes that adjusting global warming below two degrees Celsius above pre-industrial levels, the cornerstone target of the Paris climate treaty in 2015, “allows rates near-current biosphere productivity, conserving most of the earth’s carbon buildup. “
The Earth has warmed at least 1.1C so far, and is currently on track to heat another two or three levels by the end of the century unless emissions are reduced quickly and significantly.
In 2019, a football field of primary, old-growth trees was destroyed in the tropics every six seconds – about 38,000 square kilometers (14,500 square miles) in total, according to satellite data.
© Agence France-Presse