Can terrestrial ecosystems move from being carbon sinks to carbon sources in the future?
That’s one of the questions a team of scientists led by Katharyn Duffy intended to answer in their recent study. They aimed to find out if climate change-induced temperature changes would bring carbon uptake and release from terrestrial ecosystems to a tipping point.
Forests and other terrestrial ecosystems play an important role in climate change. They absorb about 30 percent of man-made CO2 emissions and thus represent an important carbon sink. Vegetation is central to this, as it is responsible for the exchange of CO2 between the land and the atmosphere. Via photosynthesis, CO2 is absorbed, converted and stored as carbon in biomass. During respiration or decay, plants release the greenhouse gas back to the atmosphere. Both processes are dependent on temperature. If the temperature rises, plant respiration and thus CO2 emissions increase. In contrast, photosynthetic performance will reach a tipping point at which it starts to decrease, so that above a certain temperature, CO2 emission will be higher than CO2 uptake.
The study uses global data from the largest continuous carbon flux monitoring network (FLUXNET) to derive temperature response curves for global land carbon uptake. The results show that complex ecosystems in particular, such as rainforests and boreal coniferous forests, could lose close to half of their carbon storage potential as early as 2040. By 2100, even half of the terrestrial ecosystems could reach the tipping point at which CO2 release outweighs CO2 uptake.
Some experts were critical of the results of the study, which can be read in detail here (only in German): https://www.sciencemediacenter.de/alle-angebote/research-in-context/details/news/land-oekosysteme-schon-bald-kohlenstoff-quellen-statt-senken/
Regardless of the study’s results and the justified criticism in the scientific community or contrary results in other studies, it is of great importance to minimize man-made greenhouse gas emissions and to recognize the importance of terrestrial ecosystems – not only in terms of carbon storage. Measures relating to LULUCF (Land Use, Land-Use Change, and Forestry), as agreed upon in major international conventions such as the Kyoto Protocol and the Paris Agreement, must be taken seriously and implemented to achieve the climate targets anchored therein. The protection of forests and ecosystems is a priority; any use must be ecologically based and sustainable. This is the only way to maintain the functionality of ecosystems so that we do not lose them as supporters in the climate crisis.
K.A. Duffy, C. R. Schwalm, V. L. Arcus, G. W. Koch, L. L. Liang, L. A. Schipper (2021).
How close are we to the temperature tipping point of the terrestrial biosphere?