Rising carbon dioxide (CO₂) levels can reverse the drying effects of predicted higher temperatures on semi-arid rangelands, according to a study published today in the scientific journal Nature by a team of USDA and university scientists.

Warmer temperatures increase water loss to the atmosphere, leading to drier soils. In contrast, higher CO₂ levels cause leaf stomatal pores to partly close, lessening the amount of water vapor that escapes and the amount of water plants draw from soil. This new study finds that CO₂ does more to counterbalance warming-induced water loss than previously expected. In fact, simulations of levels of warming and CO₂ predicted for later this century demonstrated no net change in soil water, and actually increased levels of plant growth for warm-season grasses.

"By combining higher temperatures with elevated CO₂ levels in an experiment on actual rangeland, these researchers are developing the scientific knowledge base to help prepare managers of the world's rangelands for what is likely to happen as climate changes in the future," says Edward B. Knipling, administrator of the Agricultural Research Service (ARS).

The results cover the first four years of the eight-year Prairie Heating and CO₂ Enrichment (PHACE) experiment on native northern mixed grass rangeland. The study is being conducted by the ARS Rangeland Resources Research Unit (RRRU) at the High Plains Grasslands Research Station near Cheyenne, WY.

ARS plant physiologist Jack Morgan leads the study, which uses both CO₂ pipelines and thermal infrared heaters to simulate global warming conditions predicted for the end of the century.

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