Climate Models May Overestimate Forest Carbon Storage by 30%, New Study Warns
Forests may absorb significantly less carbon dioxide in the future than previously expected, according to new research suggesting that climate change is slowing tree growth despite rising levels of atmospheric carbon dioxide. The findings raise fresh concerns over the accuracy of current climate models and the world’s ability to limit global warming.
The study, published on 18 June in Geophysical Research Letters, found that one of the world’s most widely used land surface climate models could overestimate the future carbon storage potential of forests by as much as 30%. Researchers say the discrepancy stems from a long-held assumption that tree growth and photosynthesis occur at the same rate, an idea increasingly challenged by ecological evidence.
Scientists found that while trees continue to photosynthesise, hotter and drier conditions caused by climate change can significantly slow their physical growth. This means forests may absorb carbon without converting as much of it into new wood and biomass, reducing their long-term capacity to lock away greenhouse gases.
The research team analysed data collected over eight years from broadleaf and conifer forests in Switzerland before comparing the findings with projections from a widely used open-source land surface model. Their analysis indicated that existing models may overestimate growth by up to twice for broadleaf trees and three times for conifer species, leading to inflated projections of future carbon storage.
The researchers believe the slowdown is linked to reduced turgor pressure, the water pressure inside tree cells that enables cell division and growth. Although photosynthesis can continue under these conditions, limited cell expansion means trees store less carbon than models currently predict.
Land ecosystems presently absorb around 27% of carbon dioxide emissions produced by fossil fuel combustion, while oceans absorb approximately 25%. The remainder accumulates in the atmosphere, driving global warming. If forests become less effective at storing carbon as temperatures rise, atmospheric CO2 concentrations could increase faster than many current climate projections suggest.
The study also highlights the growing need for closer collaboration between forest ecologists and climate modellers. Researchers argue that incorporating newly identified biological processes into land models will improve future climate projections and provide policymakers with more reliable estimates of the Earth’s remaining natural carbon sink.
The findings come as governments increasingly rely on forests and other natural ecosystems to meet climate targets and achieve net zero emissions. The authors say improving the representation of forest growth in climate models will be essential for accurately forecasting future warming and assessing the effectiveness of nature-based climate solutions.
