Grasslands could lose four times more carbon uptake under future drought conditions

Grasslands around the world face a significant threat to their capacity to absorb carbon dioxide in the future, according to a groundbreaking study published in *Science Advances*. Researchers from the University of Innsbruck have found that under projected future climate conditions—including rising CO₂ levels, increased temperatures, and prolonged drought—the carbon absorption capabilities of grasslands could decline by up to four times compared to current levels. This revelation challenges long-held assumptions in climate science about how ecosystems respond to multiple environmental stressors simultaneously.

The study was conducted over two years using specially designed ecosystem chambers that simulate future climate scenarios. These chambers allowed scientists to control and measure the flow of carbon dioxide and water within a grassland environment. By combining three major climate variables—increased atmospheric CO₂, warming, and drought—the researchers aimed to understand how these factors interact and affect critical ecological processes such as photosynthesis, respiration, and water balance.

Traditionally, climate models have treated the impacts of individual climate factors separately, assuming their combined effects are roughly additive. However, the results of this study suggest otherwise. When elevated CO₂ levels and warming are combined, their effects on plant physiology and ecosystem function appear to reinforce each other rather than simply adding up. When drought is introduced into this mix, the negative impacts on carbon uptake become disproportionately severe.

Michael Bahn, a professor of ecology and lead researcher on the project, explained that while higher CO₂ levels typically encourage plants to retain water, the increased temperatures caused by climate change significantly raise the water demands of plants. As a result, the benefits of enhanced water retention under high CO₂ conditions are outweighed by the heightened water stress induced by warming. This dynamic leads to a situation where drought's impact on carbon absorption is far worse than previously estimated.

The implications of these findings extend beyond theoretical understanding—they directly challenge existing climate models used to predict future carbon cycles and climate feedback loops. If ecosystems' responses to climate change are more complex and less predictable than previously thought, then current projections regarding the role of terrestrial ecosystems in mitigating greenhouse gas emissions might be overly optimistic.

This study was conducted in Styria, Austria, where the research team utilized a unique experimental setup that allows them to manipulate and monitor multiple climate variables simultaneously. Such comprehensive, multi-variable studies are rare globally due to the complexity and resource intensity required to conduct them. The insights gained from this research provide a clearer picture of how grasslands—a vital component of Earth’s biosphere—will respond to the multifaceted pressures of a changing climate.

Meanwhile, across Europe, extreme heat waves and droughts are becoming increasingly common and severe. Italy, for example, is experiencing a deepening ecological and agricultural crisis as the River Po rapidly dries up, threatening crops and food supplies. The river’s flow has dropped dramatically, with some sections seeing a reduction in volume from an average of 1,500 cubic meters per second in June to below 300 cubic meters per second. Saline seawater has intruded inland along the Po Delta, posing a serious threat to agriculture in the region. Farmers are struggling to protect their crops from saltwater intrusion, and the production of Parmesan cheese, a renowned product of the area, faces potential disruption.

Germany has also been severely affected by record-breaking heatwaves. Temperatures reached a staggering 41.5 degrees Celsius in parts of the country, breaking historical records. Infrastructure has suffered, with asphalt melting on roads and tram tracks being damaged in Leipzig. Authorities had to deploy water cannons to cool down citizens in cities like Berlin, highlighting the immediate human toll of extreme heat. The heatwave has claimed over 1,300 lives since early June, with the World Health Organization referring to it as a "silent killer."

Across Europe, millions of people are living under extreme heat warnings, with temperatures frequently exceeding 35 degrees Celsius. Scientists emphasize that such extreme weather patterns would have been nearly impossible just 50 years ago, underscoring the accelerating pace of climate change. The European Central Bank warns that the economic repercussions of these climatic extremes could be profound, with agriculture in heavily impacted regions potentially losing up to 7.6 percentage points of annual growth.

As the frequency and intensity of heatwaves continue to rise, the need for updated climate models becomes ever more urgent. The findings from the Austrian study highlight the necessity of incorporating complex, interacting climate factors into predictive models. Without doing so, there is a risk of underestimating the severity of future climate impacts on both natural systems and human societies.