Forests not as thirsty because of increasing carbon dioxide

Hunter College

Global warming is primarily driven by increasing emissions of greenhouse gases from human activities. Chief among these gases is carbon dioxide (CO2), which warms the planet by trapping heat that would otherwise radiate into space.

But carbon dioxide has effects on things other than the climate. In the journal Nature, Trevor Keenan of Macquarie University and his colleagues report that trees in some forests are using less water to maintain growth than they did only 20 years ago. This puzzling finding has been attributed to the increased levels of CO2, which trees use as their carbon source.

Instruments placed in various US forests have been measuring CO2 and water concentrations in the air for many years. These measurements have been correlated with the amount of CO2 locked up by trees over the same period to show that forests have become more efficient at storing carbon. More importantly, the measurements suggest that the increase in efficiency of storing carbon is six times greater than would be expected if it was just proportional to the increase in atmospheric CO2 concentration during the same period.