Plants likely to absorb more CO2 than we thought in a changing climate
The world’s vegetation has a remarkable ability to absorb carbon dioxide (CO2) from the air and store it as biomass. In doing so, plants slow climate change because the CO2 they capture does not contribute to global warming. But what would happen if more severe climate change occurs? How will vegetation respond to projected changes in atmospheric CO2, temperature and precipitation? Our study, published today in Science Advances, shows that plants can capture more CO2 than previously thought. We found the climate modeling that best fits the processes that sustain plant life consistently predicts the strongest CO2 absorption.
The most complex model had predictions 20% higher than the simplest version. Our findings highlight the resilience of plants and the importance of planting trees and preserving existing vegetation to slow climate change. While this is good news, it does not allow us to relax in the fight against climate change. The rapid increase in atmospheric CO2 means we still have to cut emissions. What happens to the CO2 absorbed by plants? Plants absorb CO2 through photosynthesis. This process uses the sun’s energy to convert or ”fix” CO2 from the air into sugars that plants use for growth and metabolic activity.
Plants release about half of that CO2 back into the atmosphere relatively quickly through respiration. The other half is used for growth and remains in the plant biomass for long periods of time – months to centuries. That biomass eventually dies and decomposes. Some of the carbon is released back into the atmosphere, but other parts enter the soil, where it can remain for hundreds of years. Therefore, if plants take up more CO2, it is likely that more carbon will be stored in vegetation and soil. The annual global carbon budget assessment shows that this “land sink” of carbon has actually increased over the past few decades.
Furthermore, increasing land carbon sinks have been largely attributed to the beneficial effects of increasing atmospheric CO2 on plant photosynthesis. This is important because carbon stored in plants and soils slows the increase in atmospheric CO2 and therefore global warming. A gap in current climate models But how do we know how much carbon has been captured and stored on land? Even more challenging is how can we predict what will happen in the future? One attempt to answer these questions is to use so-called terrestrial biosphere models. These models tell us how plants function and how they respond to changes in climate.
For example, we know from experiments that plants photosynthesize more in high CO2 concentrations but photosynthesize less when they do not have enough water. Models convey all this knowledge through mathematical equations and allow them to communicate with each other. All this knowledge? Well, not really, and that was the inspiration for our research. Although today’s terrestrial biosphere models include many processes, they do not necessarily account for all of the mechanisms and processes that we know to exist. There may not be enough data or information available to confidently represent a process throughout the world, or it may be difficult – conceptually or technically – to incorporate it into the model.
What was seen in the study? We incorporated three of those neglected processes into the well-established Australian terrestrial biosphere model. We calculated: How efficiently CO2 can move inside a leaf How plants adjust to changes in the temperature around them How they distribute nutrients in the most economical way. We used the latest data and research publications to incorporate the processes as realistically as possible. Then we were faced with a model with a strong climate change scenario and we looked at how much CO2 plants would absorb by the end of the century. We repeated this experiment with eight different versions of the model. The simplest version did not mention any of the three physical mechanisms. The most complex version accounts for all three. The results were surprisingly clear: the more complex the model, the greater the predicted CO2 uptake by plants.
Model versions that accounted for at least two mechanisms (those with greater ecological realism) consistently predicted the strongest CO2 uptake – up to 20% more than the simplest version. What does this mean for climate action? This is important news for modellers. This tells us our current models, which are generally at the low end of this complexity range, underestimate the potential for future CO2 uptake by plants. These results show that plants can be quite resilient even to severe climate change. However, we looked at it only from the physiological point of view of the plant. Other processes in the models are still overly simplified, such as the impacts of and recovery from fires and droughts.
We clearly need to understand these processes better to get a full picture of how effectively plants will absorb CO2 in the future. And last but not least, because plants help fight climate change, it is essential to preserve existing plant biomass and restore lost vegetation. But while plants may be more hard-working helpers than previously thought, they will never do the heavy lifting for us. It’s still up to us humans to fight climate change by drastically cutting fossil fuel emissions. There is no shortcut.
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