The US National Assessment, the MEA and now IPCC's Fourth Assessment Report all come to similar conclusions. Ecosystems, particularly those that are unmanaged to any great degree, are sensitive to the changes in the physical climate system that can reasonably be expected to occur over the next several decades to a century. Indeed, there are already many well-documented cases of impacts on marine and terrestrial ecosystems.
Such consequences are occurring and will occur on a background of already extremely rapid change in ecosystems, often driven by the extraction of goods and services in an unsustainable fashion by human societies. While some countries and economies are thought to have substantial adaptive capacity, many do not, especially in the developing world. Reasonable scenarios of ecological change due to climate change and other stresses could therefore result in overwhelming the adaptive capacity of even currently wealthy societies, although this is a conclusion subject to considerable uncertainty because of unknowns in the underlying science.
Continued preparation and purposeful adaptation will be necessary over coming decades. Successful adaptation will be dependent on both improvements in the underlying climate and ecological sciences and on actions by and improvements in institutions and policies that govern societal use of natural resources and ecosystem services.
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