Multiple feedbacks link changes in climate and ecosystems

Changes in climate are linked with changes in ecosystems through multiple feedbacks. Climatic change affects ecosystems primarily through changes in availability of soil resources and in disturbance regime, with multiple indirect effects that propagate through food webs and biogeochemical cycles. Changes in ecosystems, in turn, affect the climate system through changes in fluxes of trace gases, which are globally dispersed, and of water and energy, which affect climate more locally. The net effect of these multiple feedbacks often differs from effects expected from studies of a single process such as carbon exchange. For example, water-logged conditions that reduce CO2 emissions from soils enhance methane and nitrous oxide emissions; fire can increase CO2 release but alter vegetation structure in ways that reduce heat transfer to the atmosphere. When the long-term net effect of all climate feedbacks is considered, ecosystem changes that augment carbon storage do not necessarily reduce the warming potential of the atmosphere, and we cannot assume that ecosystems will “fix the problems” caused by fossil-fuel emissions. Ecosystems and the climate system are most tightly coupled through changes in water and energy exchange because of the local nature of this coupling. Frequently, changes in vegetation alter the climate system in ways that stabilize the altered vegetation, making these changes less reversible than might be expected from studies of competitive interactions. Consequently, large-scale changes in land-cover may be less amenable to reclamation than plot-scale studies would suggest. Attention to long-term net effects of multiple climate feedbacks provides a more informed basis for assessing both positive and negative consequences of large-scale changes in land cover and land use.