Plants can't grab nitrogen from the air on their own. They need soil microorganisms to convert it into a usable form first—a process called nitrogen fixation that happens in forests, grasslands, and farm fields alike. For years, climate scientists thought this process was happening at a certain rate in natural ecosystems. They were wrong. It turns out they've been overestimating it significantly.
That matters because Earth System models—the computer simulations that predict how our climate will change and inform major reports like the World Climate Report—rely on accurate nitrogen fixation numbers to calculate how much carbon plants can absorb. When those numbers are wrong, everything downstream gets skewed.
A new study led by Sian Kou-Giesbrecht at Simon Fraser University in Canada, published in PNAS, found that current climate models overestimate nitrogen fixation rates on natural surfaces by about 50 percent. That sounds technical until you see the consequence: it inflates projections of the CO2 fertilization effect—the idea that extra atmospheric carbon dioxide helps plants grow—by roughly 11 percent overall.
We're a new kind of news feed.
Regular news is designed to drain you. We're a non-profit built to restore you. Every story we publish is scored for impact, progress, and hope.
Start Your News Detox"We compared different Earth System models with current nitrogen fixation values and found that they overestimate the nitrogen fixation rate on natural surfaces by about 50 percent," explains Bettina Weber, a biologist at the University of Graz who co-led the research. "Because plants depend on this process to access nitrogen, the overestimate has meaningful consequences."
This isn't a minor accounting error. Nitrogen fixation is tangled up with the entire nitrogen cycle, which produces gases like nitrous oxide that escape into the atmosphere and affect climate processes. Getting the numbers right is the only way to make reliable predictions about how ecosystems will actually respond to climate change—not how we think they will.
Interestingly, while natural nitrogen fixation has been overestimated, agricultural nitrogen fixation has surged. Over the past 20 years, it's increased by 75 percent, driven by farming practices and fertilizer use. That's a real change, not a measurement error—and it's reshaping how nitrogen moves through the planet.
The updated findings mean climate scientists will need to recalibrate their models. It's the kind of unglamorous but essential work that keeps climate projections honest. When the stakes are global policy decisions and billion-dollar investments in climate adaptation, getting the baseline numbers right isn't optional.
