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Warmer Does Not Mean Drier

CO2 are pumped into a plot that is also warmed by infrared heaters.

Controlled concentrations of CO2 are pumped into a 3-metre diameter plot that is also warmed by infrared heaters overhead.

By Feike Dijkstra

A warmer climate causes grasslands to dry out faster, but a new study has found that more efficient water use by plants in response to rising CO2 concentrations in the atmosphere could completely offset the drying effect caused by warming.

Feike Dijkstra is a Senior Lecturer in Biogeochemistry in the Faculty of Agriculture, Food and Natural Resources at the University of Sydney. He is a research collaborator of the Prairie Heating and CO2 Enrichment experiment in Wyoming, USA.

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Global temperatures are on the rise as a result of increased greenhouse gas emissions into the atmosphere. To cope with the warmer temperatures, plants transpire more water to help them cool off. As a result, terrestrial eco­systems use more water and dry out faster.

In arid and semi-arid ecosystems, where rainfall is limited and irregular, a warmer and drier environment may have irreversible effects on plant communities. Existing plants may be displaced by plant species that are better adapted to drier conditions. This could significantly alter the arid and semi-arid woodlands and grasslands that dominate the Australian landscape and that provide an important source of forage to livestock.

Not only are global temperatures rising, but so too is the global atmospheric CO2 concentration. But unlike rising temperatures, a rise in atmospheric CO2 has a water-saving effect on plants. In a recent field experiment my colleagues and I found that the water savings caused by an increase in atmospheric CO2 could completely offset the drying effect caused by warming.

The human population emits roughly 5.5 Gt of carbon as CO2 into the atmosphere each year. If CO2 emissions are not curtailed soon, atmospheric CO2 concentrations will more than double by the end of this century. As a consequence, the Earth will be 3.5–6°C warmer in the latter half of this century...

The full text of this article can be purchased from Informit.