Global shift in plant water use efficiency

A modeling study suggests that the decrease in the carbon isotopic ratio (13C/12C) of atmospheric carbon dioxide (CO2) over the past few decades has been slower than that predicted based on fossil-fuel derived CO2 emissions, suggesting a shift in plant leaf traits in response to increased atmospheric CO2 that reflects increased efficiency of water use by plants relative to the past.

Article #16-19240: "Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis," by Ralph F. Keeling et al.