Terrestrial ecosystems at a carbon tipping point?

Date: 19 September 2017

Introduction: In a new study in Nature Ecology and Evolution, an international science team, including Ivan Janssens (UAntwerpen), shows that ecosystems are on the verge of capturing lower amounts of carbon.

This carbon tipping is crucial, since reduced CO2 uptake could fasten climate change. In the past, plants have mostly profited from the positive effects of increasing CO2-concentrations and atmospheric nitrogen deposition, in combination with a longer growing season. As a result, they captured extra CO2, de facto helping us in our battle against climate change.

However, the negative effects of climate change (more frequent heat waves, long droughts,…) now threaten to take over, as shown by an international scientist consortium, including Ivan Janssens (Global Change Ecology Centre, research group Plants and Ecosystems). “Earth is at a tipping point, where we are moving from a period where fertilisation effects were dominant and ecosystems became more green and productive, to a period dominated by climate warming, where the opposite happens and terrestrial ecosystems become less and less productive.”

This is not only relevant for the production of e.g. food and wood, but also for the climate warming itself. Forest and grasslands capture about 1/3 of the human CO2-emissions. If ecosystems become less active sinks in the carbon cycle, this a bad news for the Paris Climate agreement, where it was agreed to reduce human carbon emissions to a level below the natural carbon uptake.

“Increasing drought and heat waves are not the only problem”, Ivan explains. “Faster plant growth not only requires increased carbon uptake. Plants also need other nutrients including phosphorus and potassium. But in contrast to nitrogen – that enters the atmosphere through e.g. exhaust gases and livestock farming – other nutrients are not atmospherically supplied. Most soils do contain substantial amounts of phosphorus, but this is bound strongly to minerals and less available to plants.”

The scientists indicate that we have to be cautious for a cascading effect, where reduced contribution of vegetation to carbon uptake fastens climate warming. The study, published in Nature Ecology and Evolution, shows that climate change could quickly fasten as we approach previously unknown tipping points. A quick and purposeful implementation of the climate agreements is therefore quintessential.

Terrestrial ecosystems are on the verge of capturing lower amounts of CO2. (Photo: WWF)