Climate-regulation services of natural and agricultural ecoregions of the Americas

Terrestrial ecosystems regulate climate through both biogeochemical (greenhouse-gas regulation) and biophysical (regulation of water and energy) mechanisms1,2. However, policies aimed at climate protection through land management, including REDD+ (where REDD is Reducing Emissions from Deforestation and Forest Degradation)3 and bioenergy sustainability standards4, account only for biogeochemical mechanisms. By ignoring biophysical processes, which sometimes offset biogeochemical effects5,6, policies risk promoting suboptimal solutions1,2,4,7–10. Here, we quantify how biogeochemical11 and biophysical processes combine to shape the climate regulation values of 18 natural and agricultural ecoregions across the Americas. Natural ecosystems generally had higher climate regulation values than agroecosystems, largely driven by differences in biogeochemical services. Biophysical contributions ranged from minimal to dominant. They were highly variable in space, and their relative importance varied with the spatio-temporal scale of analysis. Our findings reinforce the importance of protecting tropical forests7,10,12,13, show that northern forests have a relatively small net effect on climate5,10,13, and indicate that climatic effects of bioenergy production may be more positive when biophysical processes are considered14,15. Ensuring effective climate protection through land management requires consideration of combined biogeochemical and biophysical processes7,8. Our climate regulation value index serves as one potential approach to quantify the full climate services of terrestrial ecosystems. Anthropogenic land use has been, and will continue to be, a major driver of the climate system6,16–18. In terms of biogeochemical drivers, land-use change and agriculture together account for over 25% of global greenhouse-gas (GHG) emissions19. From 1990 to 2007, gross CO2 emissions from tropical deforestationwere equal to ∼40% of global fossil fuel emissions18. In recent years, agriculture has contributed∼14%of total global GHG emissions19,20. Terrestrial ecosystems also strongly affect climate through their control over albedo and evapotransipiration5,6,8,16,21,22. Vegetated surfaces—especially forests—typically have lower albedos than bare ground and therefore absorb more incoming solar radiation. The reduction in net radiation (Rn) associated with deforestation has a cooling effect on the climate5,22,23— sometimes even outweighing GHG-induced warming5,18. Counteracting this, clearing vegetation reduces evapotranspiration and associated latent heat flux (LE). Without the vegetation, energy normally used to evaporate water instead heats the land