Risk of severe climate change impact on the terrestrial biosphere

Abstract

The functioning of many ecosystems and their associated resilience could become severely compromised by climate change over the 21st century. We present a global risk analysis of terrestrial ecosystem changes based on an aggregate metric of
\njoint changes in macroscopic ecosystem features including vegetation structure
\nas well as carbon and water fluxes and stores. We apply this metric to global
\necosystem simulations with a dynamic global vegetation model (LPJmL) under
\n58 WCRP CMIP3 climate change projections. Given the current knowledge of
\necosystem processes and projected climate change patterns, we find that severe
\necosystem changes cannot be excluded on any continent. They are likely to occur (in > 90% 
\nof the climate projections) in the boreal–temperate ecotone where heat and drought stress might
\nlead to large-scale forest die-back, along boreal and mountainous tree lines where the temperature
\nlimitation will be alleviated, and in water-limited ecosystems where elevated atmospheric
\nCO2 
\nconcentration will lead to increased water use efficiency of photosynthesis. Considerable
\necosystem changes can be expected above 3 K local temperature change in cold and tropical
\nclimates and above 4 K in the temperate zone. Sensitivity to temperature change increases
\nwith decreasing precipitation in tropical and temperate ecosystems. In summary, there is a
\nrisk of substantial restructuring of the global land biosphere on current trajectories of
\nclimate change.