(170 pages) Ecological thresholds occur when external factors, positive feedbacks, or nonlinear instabilities in a system cause changes to propagate in a domino-like fashion that is potentially irreversible. Atmospheric carbon dioxide has reached levels unprecedented in possibly the last 24 million years. CO2 concentrations have risen by 34%, mostly in the last several decades. Global temperature is higher than at any time in the last 160,000 years. One of the ways that a rapidly changing climate may affect ecosystems is by causing sudden, irreversible effects that fundamentally change the function and structure of the ecosystem with potentially huge impacts to human society. Thresholds pose perhaps the greatest challenge currently facing climate change scientists. There is clear evidence that climate change has the potential to increase threshold changes in a wide range of ecosystems, but the basic and practical science necessary to predict and manage these changes is not well developed. A sense of urgency regarding thresholds exists because of the increasing pace of change. These challenges include the potential for major disruption of ecosystem services and the possibility of social upheaval that might occur.
The report has found non linear (domino-effect abrupt changes) ecosystem reactions occurring in the North Atlantic, North Pacific and Bering Seas, in the California Ocean Current, Alaskan spruce forests and semi-arid forests, scrublands and grasslands of the Great Basin of the American West and around the world. These abrupt changes are happening now and are well established. Impacts consist of the collapse of species populations, unprecedented insect infestations, unprecedented fire outbreaks.
Projected abrupt ecosystem changes that are showing signs of beginning include the Rapid reduction of Arctic sea ice coverage, drying of prairie pothole environments across significant areas of the upper Great Plains that are primary habitat for major waterfowl populations in North America, sub-Arctic tundra are changing to a shrub land forest ecosystems, rapid loss of wetlands / permafrost ecosystems across the sub arctic and Arctic happening as catastrophic drainage of melted permafrost occurs, rapid changes in forested permafrost areas to wetlands areas as permafrost melts, killing the original forest habitat in wide areas is beginning to occur, multiple rapid ecosystem changes in the Bering Sea including marine mammals, birds, fish and primary productivity organisms.
Three and half million acres of pinyon pine, two million acres of ponderosa pine and two million acres of Lodgepole pine have died. Significant kill is beginning to occur in whitebark pine and quaking aspen.