Terrestrial and marine ecosystems absorb approximately half of the carbon dioxide coalthat humanity emits into the atmosphere. This makes them our key natural allies in reducing global warming. Scientists have been warning for years, however, that over time their potential to store “excess” CO2 will increasingly weaken.
In a study published in the journal “Nature Geoscience” scientists looked at the situation in forest ecosystems. The most important conclusion?
Forest fires and the “carbon budget”
WITH reason growing number of fires, forests around the world are increasingly becoming a significant source of CO2 emissions. This accelerates the depletion of our remaining “carbon budget” and, as a result, makes it more difficult to slow global warming.
The 2015 Paris Agreement states that countries will strive to limit the temperature increase to 1.5°C, and in the worst case – well below 2°C (relative to the pre-industrial period). The mentioned “carbon budget” is the estimated amount of carbon dioxide that we can still release into the atmosphere in order not to exceed these thresholds. However, its calculation is usually based on emissions from direct human activities.
As the authors of the study write in Nature Geoscience, this puzzle “lacks the feedback between fire, vegetation and carbon” that are “essential for understanding the future resilience of ecosystems.”
When the researchers added this missing element to the models, their calculations showed that humanity's remaining “carbon budget” was reduced by about 5 percent. This applies to both the goal of limiting warming to 1.5°C and 2°C. In the first case, the “budget” is reduced by 25 billion tons of CO2, and in the second – by 64 billion tons.
Forests absorb less and less
But it doesn't end there. Every forest fire has a double impact on the climate. On the one hand, it leads to carbon dioxide emissions (mainly from burned trees), and on the other – it reduces the ability of forest ecosystems to absorb CO2.
Meanwhile, according to the study, the level of global warming at which fires forests have begun to have a significant impact on global carbon storage has already been exceeded. It was 1.07°C (with an uncertainty range from 0.8 to 1.34°C), and currently the Earth is already warmer by approximately 1.2°C (WMO, 2023).
What does this mean? “We conclude that forest fires already play a major role in reducing the effectiveness of land-based carbon sinks,” the researchers write in the study. “While limiting warming to 1.5°C is still necessary to avoid the worst impacts of climate change, in many cases we are already reaching the point of significant change in carbon- and biodiversity-rich ecosystems,” they add.
A grim reality
Otherwise thing To put it simply: forest fires are a “now” problem, not just a “then” problem.
“Our findings highlight a grim reality: wildfires are not just a future problem, they are affecting our planet now. As temperatures rise, wildfires are pushing natural carbon sinks further towards becoming sources of carbon dioxide emissions – comments Dr. Douglas Kelley, co-author of the study from the British Center for Ecology and Hydrology.
“This makes defending the 1.5°C threshold in the Paris Agreement even more critical to prevent escalating impacts,” adds Dr Chantelle Burton of the Met Office Hadley Centre, lead author of the study.
The researcher points out that in some parts of the world, losses caused by forest fires will not be significant until warming reaches 2.0°C. – So we can still limit the worst effects if we reduce emissions, says Dr. Burton.
What to do?
The authors of the study indicate that forest fire management policy should take into account not only technical aspects, but also social responsibility. On the one hand, this means that there should be consequences for fires that are deliberately set by humans. On the other – that people promoting and building local capacity to adapt, mitigate and respond to fires should be financially rewarded.
Another important recommendation is to take into account the impact of forest fires in climate strategies. This will allow for better assessment and management of global warming risks.
It is also extremely important, if not the most important, for world leaders to take decisive action to reduce greenhouse gas emissions. Because for years, instead of decreasing, they are constantly increasing (even slower, but still).
“The failure of the international community to reduce global emissions means that we now have to live with inevitable changes. Many people around the world will have to live with more fire in their daily lives, and ecosystems will inevitably change,” concludes Prof. Richard Betts, another of the study's authors.
Feedback
It is worth adding that forest fires are not the only feedback that worries scientists. A similar threat is, for example, the rapid melting of the ice cover. This reduces the planet's ability to reflect sunlight back into space and, as a result, accelerates global warming.
In this way, we are getting closer and closer to tipping points, beyond which the processes driving climate change will fuel themselves. That is, regardless of whether humanity continues to emit greenhouse gases or eventually stops doing so (see: “Stable” or “greenhouse” Earth?).
About the study
The study used advanced global climate models and models of phenomena occurring on the Earth's surface, including the impact of vegetation and fires. They simulate the way plants grow, compete for resources and respond to environmental changes. The models also took into account the nutrients plants need and how climate change affects forest fires.
By examining both historical data and future global warming scenarios, the research team identified critical temperature thresholds at which wildfires cause significant changes in tree cover and carbon storage.
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