Earth’s plants may not be the climate saviours scientists once hoped for. New research has revealed that vegetation across the planet is absorbing significantly less carbon dioxide than climate models have predicted for years, raising fresh concerns about the world’s ability to slow global warming naturally.
For a long time, scientists believed that rising carbon dioxide levels in the atmosphere could stimulate faster plant growth, allowing forests and other ecosystems to absorb more carbon and partially offset climate change. However, this benefit depends heavily on the availability of nitrogen, a critical nutrient that plants need to grow. The latest findings show that the natural supply of nitrogen has been seriously overestimated.
The study, involving researchers from the University of Graz and an international team of scientists, found that natural biological nitrogen fixation has been overstated by around 50 percent in major Earth system models. Nitrogen fixation is a process carried out by microorganisms in soil that converts nitrogen into a form plants can use. If this process is weaker than assumed, plants simply cannot take in as much carbon dioxide as expected.
According to the researchers, this overestimation has led to an exaggerated view of the so-called “carbon dioxide fertilisation effect.” When corrected, the models show an overall reduction of about 11 percent in the amount of carbon plants are expected to absorb from the atmosphere. This means nature’s buffering capacity against climate change is smaller than previously believed.
Bettina Weber, a biologist at the University of Graz and a co-author of the study, explained that while nitrogen fixation has increased sharply due to modern agriculture, it has been significantly overestimated in natural ecosystems. This imbalance affects how scientists predict future climate conditions, especially as nitrogen-related gases released into the atmosphere can further influence warming.
The research team compared real-world nitrogen fixation data with values used in widely applied climate models, including those that inform major global climate assessments. Their updated analysis was published in the journal *Proceedings of the National Academy of Sciences* and is expected to prompt revisions to existing climate projections.
Scientists say these findings add another layer of uncertainty to future climate forecasts and highlight the need for more accurate modelling of natural processes. As global carbon emissions continue to rise, relying on plants to absorb excess carbon may no longer offer the level of protection once assumed, underscoring the urgency of reducing emissions at their source.