Forests may be becoming more efficient in their use of water as atmospheric carbon dioxide levels rise, reports a new study in Nature. The findings are based on data from 300 canopy towers that measure carbon dioxide and water flux above forests at sites around the world, including temperate, tropical, and boreal regions. The researchers found that plants are becoming more water efficient as CO2 levels rise. While the findings are consistent with forecasts using models, the rate of efficiency gain is higher than expected.