Climate Change Projections Simulated to Understand Impact of Higher CO2 Levels

Study finds that CO2 does more to counterbalance warming-induced water loss than previously expected.

Published on: Aug 5, 2011

USDA's Agricultural Research Service is simulating the global warming conditions predicted for the end of the century using CO2 pipelines and thermal infrared heaters to study the impact of rising carbon dioxide levels on semi-arid rangelands. The new study finds that CO2 does more to counterbalance warming-induced water loss than previously expected. In fact, the simulations demonstrated no net change in soil water, and actually increased levels of plant growth for warm-season grasses. Based on the findings, warmer temperatures would likely play a role in changing the relative success of various grass types.

ARS Plant Physiologist Jack Morgan says only the warm-season grasses had their growth boosted by CO2 and warmer temperatures. If that leads to a competitive advantage for warm-season grasses he says it could increase the challenges faced by those ranchers who desire cool-season grasses for early season forage. Morgan says more research is needed to determine how the water-savings effect applies over the long-run and in other types of semi-arid rangelands and croplands in semi-arid areas. He adds that it's important to understand the CO2 only offset the direct effects of warming on soil water - and is unlikely to offset more severe drought due to combined warming and reduced precipitation.

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

"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," said Edward B. Knipling, administrator of the Agricultural Research Service, USDA's principal intramural scientific research agency.

Morgan said more research is needed to determine how the water-savings effect applies over the long run and in other types of semi-arid rangelands as well as to croplands in semi-arid areas. The study, which in addition to ARS is supported by grants from the National Science Foundation, the U.S. Department of Energy, and USDA's National Institute of Food and Agriculture, is expected to be completed in 2013.