Satellites reveal contrasting responses of regional climate to the widespread greening of Earth

Increasing terrestrial biomass has important impacts on the climate that affects it. The vegetation-climate loop Just as terrestrial plant biomass is growing in response to increasing atmospheric CO2, climate change, and other anthropogenic influences, so is climate affected by those variations in vegetation. Forzieri et al. used satellite observations to analyze how changes in leaf area index (LAI), a measure of vegetation density, have influenced the terrestrial energy balance and local climates over the past several decades. An increase in LAI has helped to warm boreal zones through a reduction of surface albedo and to cool arid regions of the southern hemisphere by increasing surface evaporation. Furthermore, more densely vegetated areas displayed a greater capacity to mitigate the impact of rapid climate fluctuations on the surface energy budget. Science, this issue p. 1180 Changes in vegetation cover associated with the observed greening may affect several biophysical processes, whose net effects on climate are unclear. We analyzed remotely sensed dynamics in leaf area index (LAI) and energy fluxes in order to explore the associated variation in local climate. We show that the increasing trend in LAI contributed to the warming of boreal zones through a reduction of surface albedo and to an evaporation-driven cooling in arid regions. The interplay between LAI and surface biophysics is amplified up to five times under extreme warm-dry and cold-wet years. Altogether, these signals reveal that the recent dynamics in global vegetation have had relevant biophysical impacts on the local climates and should be considered in the design of local mitigation and adaptation plans.