Scientists predict trees will grow faster as they gobble up carbon dioxide until the end of the century. But experts aren't sure they'll be able to take up carbon dioxide past 2100, they warn in a study highlighting the importance of preserving forests in the fight against global warming.
The team behind the study published in the journal Nature Climate Change wanted to forecast whether trees can continue soaking up the greenhouse gas in the future.
The team looked at 138 existing studies on grassland, land used for crops, shrubland, and forests where levels of carbon dioxide were elevated. These experiments included approaches like growing plants in special chambers and fumigating forests with carbon dioxide. They also looked at the symbiotic relationship between plants and fungi which helps both to thrive, and data on soil nutrients like nitrogen and phosphorus which trees need to turn carbon dioxide into food.
Rob Jackson, chair of the Earth System Science Department at Stanford and co-author of the paper published in Nature Climate Change explained to Newsweek: "Over the last three or four decades, forests and terrestrial systems in general have absorbed almost a quarter of all fossil fuel emissions released into the air."
"A large part of that gain has been because of carbon dioxide fertilization (carbon dioxide as plant food). Will this extra growth continue? Will we continue to get 'interest' on our forest principal to the tune of billions of tons of carbon dioxide each year?
"Our study suggests 'yes'. If 'no,' then carbon dioxide concentrations in the atmosphere will rise faster for the same level of emissions," he warned.
The figures revealed that the amount of carbon dioxide expected to be released by 2100 could cause the biomass of plants—or weight in layman's terms—to increase by 12 percent by feeding on the gas. At current rates of global anthropogenic emissions, this amounts to five to six years of carbon dioxide emissions.
The team also found interactions between nitrogen, phosphorus, and the relationship between fungi and plants largely drive how plants will use carbon dioxide in the coming decades.
"Our results highlight the key role of terrestrial ecosystems, in particular forests, in mitigating the increase in atmospheric carbon dioxide resulting from anthropogenic emissions," the authors wrote.
They went on to warn: "Thus, if deforestation and land use changes continue decreasing the extent of forests, or if warming and other global changes diminish or reverse the land carbon sink, we will lose an important contribution towards limiting global warming."
Jackson told Newsweek: "We were pleased to find that forests appear likely to grow even faster in the future as a result of CO2 fertilization." But Jackson stressed the amount of carbon dioxide used by trees isn't enough to halt climate change. "They aren't, and won't be, a substitute for the first order of business—cutting fossil fuel emissions," he said.
This is the latest project which has seen experts assess the role that plants play in climate change. Last week, the United Nations' Intergovernmental Panel on Climate Change released a report highlighting the importance of land, including forests, on controlling climate change. And a study published in Science in July showed restoring forests on a global scale could help ease the effects of climate change.
"Preserving and restoring our forests doesn't just fight climate change," explained Jackson. "Forests purify our water and air, reduce soil erosion, and harbor most of the world's biodiversity. We help much more than climate by taking care of them."
César Terrer, lead author of the study and postdoctoral scholar in Earth system science at Stanford University School of Earth, Energy and Environmental Sciences, commented in a statement: "Keeping fossil fuels in the ground is the best way to limit further warming. But stopping deforestation and preserving forests so they can grow more is our next-best solution."
Terrer commented: "We have already witnessed indiscriminate logging in pristine tropical forests, which are the largest reservoirs of biomass in the planet. We stand to lose a tremendously important tool to limit global warming."
Professor Patricia Thornley, director of the Energy and Bioproducts Research Institute at the U.K.'s Aston University, who did not work on the research, told Newsweek: "One of the issues raised in the report is that the key constraint on achieving this enhanced biomass growth is the availability of nitrogen (primarily) and phosphorus (secondary).
"That draws attention to the fact that we need to be really careful about management of nutrients globally, ensuring that nitrogen and other plant nutrients are appropriately applied and not wasted or allowed to accumulate and cause pollution."
However, she added: "There are large uncertainties acknowledged in the report and so we cannot be completely confident that this additional growth will materialize, but also it is not completely clear how the work has accounted for changes in water availability, which could also have strong impacts."
This article has been updated with comment from Professor Patricia Thornley.
