CLIMATE MODELS will have to be changed after research into the uptake of carbon dioxide by plants was published. It shows the availability of water is more important to plant carbon uptake than temperature. The findings help to explain contradictions between model predictions and measurements on the ground.
It has to do with the Earth’s natural cycle of breathing in and out carbon dioxide, according to scientists at a press conference at the Euroscience Open Forum in Turin to announce the research.
The details are in two research papers published this morning by the journal Science in its online publication Sciencexpress. Teams at the Max Planck Institute in Germany led the research, which involved scientists from 10 other countries around the world.
The institute’s Christian Beer and colleagues used models and field data to measure the amount of carbon “inhaled” by the Earth’s global plant life. Plants take up carbon dioxide through photosynthesis and take a large volume of carbon out of the atmosphere. Carbon mainly as carbon dioxide is blamed for global warming.
Dr Beer and his colleagues looked at eight years of field measurements recording the amount of carbon plants take in. This was collected by Fluxnet, an international collaboration to study exchanges of carbon dioxide between the Earth and the atmosphere. This data, combined with model measurements, indicated that the world’s plant life inhales about 123 billion tonnes of carbon each year.
The phytoplankton in the oceans take up a similar amount, stated Dr Markus Riechstein of the institute. The Earth then “exhales” as soils and other natural sources return almost all this carbon back into the atmosphere – apart from about two billion tonnes.
This retained carbon means that carbon levels in the atmosphere should be falling, Dr Riechstein said. But this benefit is lost as the fossil fuels we burn discharge between eight and nine billion tonnes of carbon, leaving us with a net excess of carbon and rising greenhouse gas levels.
The second study, led by Dr Miguel Mahecha from the institute, helped to settle a scientific dispute about the effects of rising temperatures on plants and whether the amount of carbon they took up rose or fell as temperatures climbed. They also wanted to gauge the influence of other factors, especially water availability.
Dr Mahecha found temperature variations had less of an effect than the models suggested. The models predicted a doubling of carbon uptake with a 10 degree rise in temperature but in fact there was only a 1.4-times rise in uptake.
The team also found water was a key element in how plants responded. When water is available, plants take up carbon dioxide readily even as the temperature rises. But if water becomes scarce the plants shut down, conserving water and slowing photosynthesis.