Even plants cannot help cool earth if CO2 is in excess: Study

Scientists have found that plants will directly warm the land surface when there is excess CO2.

Last Updated: May 17, 2010, 13:10 PM IST

Mumbai: Contrary to the belief that plants could help cool earth, scientists have found that they will directly warm the land surface when there is excess carbon dioxide in the atmosphere.

A recent global scale model study points to an emerging consensus that the physiological effects of increasing atmospheric CO2 on plants on land will contribute to global warming beyond what is caused by the `radiative` effects of CO2, Prof Govindasamy Bala of Indian Institute of Science (IISc), Bangalore, one of the authors of the study, told a news agency.

Carbon dioxide warms the earth because it is a greenhouse gas. However, elevated CO2 in the atmosphere causes plants to transpire less and provide less `evaporative cooling`, he said.

"For scientists trying to predict global climate change in the coming century, the study underscores the importance of including plant biology in their climate models," Bala, who conducted the study jointly with Long Cao and Ken Caldeira of Carnegie Institution for Science at Stanford University, said.

Explaining plant physiology, Bala said, "The CO2-physiological effect arises from a change in plant transpiration rate under elevated atmospheric CO2".

"On a hot day, we sweat more, release more water through pores in our skin and cool ourselves. Similarly, while doing photosynthesis (food production process in plants using photons from sun), plants cool the environment by releasing water through the pores called stomata on the surface of leaves," Bala said.

"But stomata opens less widely and the canopy sweats
less when CO2 is increased which causes a decline in plant
transpiration and thus warming of the land surface," he said.