Ecosystems & Global Climate Change: A Review of Potential Impacts on U.S. Terrestrial Ecosystems and Biodiversity

Eileen Claussen, President, Pew Center on Global Climate Change

Natural ecosystems are one of our most precious resources, critical for sustaining life on the planet. The benefits humans derive from ecosystems are varied, from marketable products such as pharmaceuticals, to recreational opportunities such as camping, to ecosystems services such as erosion control and water purification. For many people, nature plays a powerful spiritual and aesthetic role in their lives, and many place a high value on the existence of wilderness and nature for its own sake. Despite the critical roles ecosystems play, these areas are increasingly threatened by the impacts of a growing human population through habitat destruction and air and water pollution. Added to these stresses comes a new threat -- global climate change resulting from increased greenhouse gas concentrations in the atmosphere.

"Ecosystems and Global Climate Change" is the fifth in a series of Pew Center reports examining the potential impacts of climate change on the U.S. environment. It details the very real possibility that warming over this century will jeopardize the integrity of many of the terrestrial ecosystems on which we depend. Among the many key issues raised are:

• With warming, the distribution of terrestrial ecosystems will change as plants and animals follow the shifting climate. The eastern United States will likely lose many of its deciduous forests as the climate zones shift northwards, while more mountainous regions, like portions of the West, will see species and ecosystems migrate up mountain slopes from lower elevations.
  
  
• Both the amount and rate of warming predicted represent a threat to our nation's biodiversity. Certain species may face dwindling numbers and even extinction if they are unable to migrate fast enough to keep up with the changing climate. Likewise, as warming shrinks the zone of cold conditions in upper latitudes and on mountains, the future of species that depend on such climates will be in jeopardy.
  
  
• Climate change is likely to alter ecosystem composition and function — that is, which species make up an ecosystem and the way in which energy and materials flow through these systems. These modifications are bound to alter the amount and quantity of the various goods and services ecosystems provide.
  
  
• Ecosystems are inherently complex and difficult to model, and our ability to predict exactly how species and ecosystems will respond to a changing climate is limited. This uncertainty limits our ability to mitigate, minimize, or ameliorate the effects of climate change on terrestrial ecosystems. In order to maximize nature's own potential to adapt to climate change, we must continue to support existing strategies to conserve biodiversity and protect natural ecosystems.
  
  

The authors and the Pew Center gratefully acknowledge the input of Drs. Anthony Janetos and Chris Field on this report. This report also benefited from comments received at the Pew Center's July 2000 Workshop on the Environmental Impacts of Climate Change. The Pew Center would also like to thank Joel Smith and Brian Hurd of Stratus Consulting for their assistance in the management of this Environmental Impacts Series.