For many years, scientists believed rising CO₂ levels would help Earth’s plants significantly slow climate change. As carbon dioxide increased in the atmosphere, plants were expected to grow faster and absorb more CO₂, acting as a natural brake on global warming.
However, new findings show this assumption was too optimistic. Plants absorb far less carbon dioxide than climate models once predicted, mainly due to a hidden but essential factor: nitrogen.
This discovery is important because climate models shape predictions of future warming and influence global climate policies. When models overestimate how much CO₂ plants can absorb, they also underestimate how fast and severe climate change may become. The issue does not lie with plants themselves. Instead, it lies in the limited nutrients plants need to grow and pull carbon from the atmosphere.
The hidden role of nitrogen in plant growth
Plants need more than sunlight, water, and carbon dioxide to grow. One of the most important nutrients for plants is nitrogen. Without enough nitrogen, plants cannot build proteins, grow new leaves, or store extra carbon.
Although nitrogen is everywhere in the air, plants cannot use it directly. Nitrogen must first be converted into a usable form. This process is called nitrogen fixation. It happens mostly in soil and depends on tiny microorganisms.
For a long time, climate models assumed that natural ecosystems had plenty of nitrogen available. Because of this assumption, models suggested that plants could respond strongly to rising CO₂ levels. This response is known as the CO₂ fertilization effect.
In simple terms, higher CO₂ was expected to mean faster plant growth and more carbon stored in trees, grasses, and soils. However, scientists recently took a closer look at how much nitrogen fixation actually happens in nature. The results were surprising. Natural ecosystems produce far less usable nitrogen than earlier estimates suggested. This means plants often lack the nutrients they need to fully take advantage of extra CO₂ in the air.
At the same time, nitrogen fixation has increased sharply in agriculture. Farming activities, including fertilizer use and crop cultivation, have boosted nitrogen availability on farmland. Over the past two decades, nitrogen fixation linked to agriculture has grown by about three-quarters.
Still, this increase does not help natural forests, grasslands, and wild ecosystems absorb more carbon. These natural areas are the ones climate models rely on most when estimating how much CO₂ the planet can store.
Why climate models overestimated plant CO₂ uptake
Earth system models are complex computer programs. Scientists use them to simulate interactions between the atmosphere, land, oceans, and living organisms. These models help estimate future climate conditions.
Many of these models included nitrogen cycles. However, they relied on outdated or overly generous estimates of natural nitrogen fixation. When researchers compared real-world nitrogen data with model assumptions, they found a large gap. Natural nitrogen fixation on land surfaces was overstated by about half.
This overestimate has serious consequences. Because plants depend on nitrogen to grow, inflated nitrogen levels led models to assume stronger plant growth than is realistic. As a result, the overall CO₂ fertilization effect was also exaggerated. New analysis shows that this effect may be reduced by around 11 percent compared to earlier projections.
This may sound like a small number. In climate science, however, even small percentage changes can make a big difference. Over decades, reduced carbon absorption by plants can mean much higher levels of CO₂ remaining in the atmosphere.
This also affects how scientists understand carbon budgets. A carbon budget estimates how much CO₂ humans can emit while staying within certain temperature limits. If plants absorb less carbon, that budget becomes smaller.
In addition, nitrogen processes produce other gases. During nitrogen conversion, gases like nitrous oxide can be released into the air. These gases are powerful contributors to climate change. If models do not correctly represent nitrogen behavior, they may also misjudge the impact of these gases on global warming.
Why correcting nitrogen data matters for climate science
Accurate climate models depend on realistic inputs. Nitrogen is one of the most important, yet complex, elements in Earth’s life-support systems. When nitrogen fixation is miscalculated, the entire picture of how ecosystems respond to climate change becomes distorted. Plants appear more resilient than they truly are. Forests seem more capable of offsetting emissions than they actually can.
Updating nitrogen data helps scientists better understand how land ecosystems interact with the atmosphere. It also improves estimates of greenhouse gas emissions linked to soil processes.
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This correction is especially important because climate models influence major global reports. Governments, researchers, and institutions rely on these assessments to plan climate strategies. Better nitrogen measurements help ensure that projections are based on real-world limits rather than optimistic assumptions.
It also highlights an important truth: nature has boundaries. Plants cannot endlessly compensate for rising emissions. Their ability to absorb carbon depends on nutrients, soil health, and biological processes that cannot simply scale up on demand. Understanding these limits does not change the science of climate change. Instead, it makes the science more precise.
By adjusting nitrogen calculations, climate models can more accurately reflect how Earth’s ecosystems behave today. This leads to clearer insights into how much carbon remains in the atmosphere and how natural systems respond under pressure.
These findings reinforce the importance of careful measurement and continuous model improvement. Climate science evolves as new data emerges. Each update helps sharpen our understanding of how the planet truly works.
As researchers refine these models, the role of plants in absorbing CO₂ is becoming clearer. They are vital allies in regulating Earth’s climate, but their capacity is not unlimited.
