Overestimated nitrogen availability has led climate models to exaggerate how much plant growth can offset rising CO2 levels.
Rising levels of carbon dioxide in the atmosphere are a major driver of climate change. At the same time, higher CO2 concentrations can encourage plants to grow faster, which in turn can help slow warming by drawing more carbon out of the air.
This benefit depends on whether plants have access to enough nitrogen. New research suggests that scientists have only recently gained a clearer picture of how much nitrogen is actually available.
As a result, the so-called “fertilizing effect” of CO2 on plant growth has been significantly overstated, according to a new study involving the University of Graz.
Natural nitrogen fixation was overstated
Plants can only use nitrogen after it has been converted into a usable form in the soil by microorganisms. This process, known as biological nitrogen fixation, takes place in both natural environments and agricultural systems.
“While this process has been significantly overestimated in nature, it has increased by 75 percent over the past 20 years due to agriculture,” explains Bettina Weber, a biologist at the University of Graz, summarizing findings published earlier this year.
Building on those results, a new study shows that calculations used in some Earth System models have now been revised. These models are widely used to assess climate trends, including in the World Climate Report. The updated analysis, published in the scientific journal PNAS, concludes that earlier estimates of nitrogen fixation were too high.
