Abstract
The surface air temperature response to vegetation changes
has been studied for the extreme case of land-cover change1–5
;
yet, it has never been quantified for the slow but persistent
increase in leaf area index (LAI) observed over the past
30 years (Earth greening)6,7
. Here we isolate the fingerprint of
increasing LAI on surface air temperature using a coupled land–
atmosphere global climate model prescribed with satellite LAI
observations. We find that the global greening has slowed
down the rise in global land-surface air temperature by
0.09 ± 0.02 ◦C since 1982. This net cooling eect is the sum
of cooling from increased evapotranspiration (70%), changed
atmospheric circulation (44%), decreased shortwave transmissivity
(21%), and warming from increased longwave air
emissivity (−29%) and decreased albedo (−6%). The global
cooling originated from the regions where LAI has increased,
including boreal Eurasia, Europe, India, northwest Amazonia,
and the Sahel. Increasing LAI did not, however, significantly
change surface air temperature in eastern North America
and East Asia, where the eects of large-scale atmospheric
circulation changes mask local vegetation feedbacks. Overall,
the sum of biophysical feedbacks related to the greening of
the Earth mitigated 12% of global land-surface warming for the
past 30 years
