Study sees climate upside in greening arid regions

Wendy Koch | USA TODAY

An upside to climate change? The issue has been blamed for many problems, including more acidic oceans and rising pollen counts, but a study released Friday suggests a benefit: Arid regions are getting greener.

Satellite data since the early 1980s have shown a flourishing of foliage worldwide, and scientists have suspected this change may be due partly to the increase in atmospheric carbon dioxide, a heat-trapping greenhouse gas emitted by the burning of fossil fuels..

Turns out, they were right because of CO2's "fertilization effect," according to a team of scientists led by Randall Donohue of the Commonwealth Scientific and Industrial Research Organization in Canberra, Australia.

Their mathematical model predicted a foliage increase of 5% to 10%, based on the 14% hike in atmospheric CO2 from 1982 to 2010, for the regions they studied: the southwestern corner of North America, Australia's outback, the Middle East and some parts of Africa.

What actually happened? Satellites showed an 11% increase in foliage after adjusting data for precipitation.

Donohue said prior research linked the rise in global vegetation to "fairly obvious climatic variables" such as rising temperatures in normally cold places or rising rainfall in typically dry areas. He said his team is the first to show a CO2 link.

"If elevated CO2 causes the water use of individual leaves to drop, plants will respond by increasing their total numbers of leaves," Donohue said in announcing the findings. The study has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

Donohue said the "fertilization effect" could also alter the types of vegetation in dry areas. "Trees are re-invading grass lands, and this could quite possibly be related to the CO2 effect," he said.. "Long lived woody plants are deep rooted and are likely to benefit more than grasses from an increase in CO2."