"Climate change will affect nature's ecosystems and the habitats that support life--from oceans to grasslands to forests. Changes are expected to alter the makeup and functioning of ecosystems, as well as some of the critical benefits that ecosystems provide to people. Climate change can threaten ecosystems that have already been weakened by other human activities such as pollution, development, and overharvesting. This fact sheet describes some of the ways that climate change affects ecosystems."
Environmental Protection Agency: http://www.epa.gov/