Washington: In a world with twice as much carbon dioxide in the atmosphere, plants could grow larger and create a cooling effect on a warming globe, but could not halt
or reverse climate change, NASA has said.
One of the main mysteries scientists face with climate change is how to project it over time, particularly how to account for Earth`s reaction to warmer temperatures, a
phenomenon known as "feedback."
It has long been known that plants -- which use carbon dioxide, sun and water to grow through the process of photosynthesis -- are able to adapt to higher carbon dioxide
levels by using nutrients more efficiently and growing bigger leaves.
"The process is called `down-regulation.` This more efficient use of water and nutrients has been observed in experimental studies and can ultimately lead to increased leaf
growth," NASA said in a statement yesterday.
But just what effect that increased plant growth would have on global warming has been difficult to predict.NASA`s new computer modelling effort, described in the
December 7 issue of the journal Geophysical Research Letters, calculated the plants` cooling effect to be -0.3 degrees Celsius (-0.5 Fahrenheit) globally.
However that number falls well short of the temperature increase of two to 4.5 degrees Celsius (3.5 to 8.0 Fahrenheit) that is the standard basis for many global warming modelling simulations.
`This feedback slows but does not alleviate the projected warming," said Lahouari Bounoua, lead author of the paper and expert at the Goddard Space Flight Center outside Washington. Bounoua`s model found that warming was on the lower scale of the widely accepted range when carbon dioxide was doubled, projecting warming of 1.94 degrees C globally, not including the 0.3 C drop for feedback.
Previous climate models have not included the larger leaf growth that would come from "down-regulation," and have projected little to no cooling from vegetation growth, the US space agency said.
This is what is completely new," said Bounoua, referring to how the model was adapted to include changed leaf growth. "What we did is improve plants` physiological response in the model by including down-regulation. The end result is a stronger feedback than previously thought."
The latest research shows "how, over time, scientists will create more sophisticated models that will chip away at the uncertainty range of climate change and allow more
accurate projections of future climate," NASA said.