Thresholds of Climate Change in Ecosystems

Final Report, Synthesis and Assessment Product 4.2

U.S. Climate Change Science Program

And the Subcommittee on Global Change Research

Lead Agency - U.S. Geological Survey

Contributing Agencies

National Oceanic and Atmospheric Administration

National Science Foundation

U.S. Department of Agriculture, Forest Service

U.S. Department of Energy

U.S. Environmental Protection Agency

Full report available at (http://downloads.climatescience.gov/sap/sap4-2/sap4-2-final-report-all.pdf).

Some gems

In addition to the gradual types of climate-related change mentioned above, there is increasing recognition that small changes in climate can trigger major, abrupt responses in ecosystems when a threshold is crossed.

Tipping point illustrations - Arctic Tundra etc.

A clear example comes from recent observations of the Arctic tundra, where the effects of warmer temperatures have included reduced snow cover duration, which leads to reduced reflectivity of the surface. Reduced reflectivity causes greater absorption of solar energy, resulting in local warming, which, in turn, further accelerates the loss of snow cover. This amplified, positive feedback effect quickly leads to warmer conditions that foster the invasion of shrubs into the tundra. The new shrubs themselves then further reduce albedo and add to the local warming. The net result is a relatively sudden, domino-like chain of events that result in conversion of the arctic tundra to shrubland, triggered by a relatively slight increase in temperature.

The Alaskan spruce bark beetle outbreak and consequent forest die-off are an example of an actual climate-induced threshold crossing. There are additional ecosystems for which conditions suggest an approaching climate-related threshold. These include coral reefs, prairie pothole wetlands, and southwestern forests. Climate-related processes that affect coral reefs include sea-level rise, ocean acidification, and the increased water temperatures that are responsible for coral bleaching events.

Prediction is beyond current capabilities

Ecological systems are multivariate in nature, but current ecological forecasting model capabilities are comparatively simple and generally do not address the possibility or consequences of thresholds. Complex situations like those involving ecological thresholds thus tend to be beyond the limits of existing predictive capabilities. The end result is surprises for managers.

Recommendations

Reliable identification of thresholds across different systems should be a national priority because of the potential for substantive surprises in the management of our natural resources.

Consideration should be given to monitoring indicators of ecosystem stress rather than the resources and ecological services of management interest.

Models generally project ecosystem trends and shifts, but do not explicitly consider the possibility of thresholds. A concerted effort must be made to understand, model, and project ecosystem responses to climate change with explicit acknowledgment of thresholds.

And the need for a panic button expressed in very grown up terms!

Recognize Need for Decisionmaking at Multiple Scales.—

Much of the recent information on climate change impacts suggests that changes are occurring more quickly than forecast only a few years ago. It is also apparent that many changes are causing secondary, or cascading, domino-like, changes in other parts of ecosystems. Management policies that were developed during relatively stable climate conditions may be inadequate for a variable world with more surprises. A shift toward multiple scales of information integration and subsequent decisionmaking can enhance and leverage existing management resources.