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Annual Public Lectures Series > Colleen Charles

Scientists and Journalists:
Getting the Point Across
June 8-12, 2009

Tuesday, June 9, 3:30 p.m.
Thresholds of Climate Change in Ecosystems
Colleen Charles, U.S. Geological Survey

Summary

A dry season, overgrazing, flooding - each of these conditions can lead to changes in an ecosystem. But with the increasing instability of our climate system, a succession of changes can drive a domino effect, propagating changes that may be irreversible in certain ecosystems.

Colleen Charles, of the U.S. Geological Survey, spoke Tuesday at the Metcalf Institute's Public Lecture Series. Her talk, the "Thresholds of Climate Change in Ecosystems," emphasized that while we don't know what conditions lead to such a tipping point, it is important that scientists attempt to find where these thresholds are to improve management strategies and to identify the ecosystem impacts of threshold changes.

For the purposes of the report, which Charles worked on with 16 authors for the U.S. Climate Change Science Program, "ecosystem threshold" is defined as "the point at which there is an abrupt change in an ecosystem quality, property or phenomenon, or where small changes in one or more external conditions produce large and persistent responses in the ecosystem."

Although we understand how some direct human stressors - such as cropping, irrigation, etc. - can affect an ecosystem, the addition of another layer of instability, such as that caused by climate change, can change the picture dramatically, "helping that ecosystem [to] quicken its pace along the trajectory of meeting its threshold," Charles said.

To help policy makers and management agencies plan for the possibility of reaching ecosystem thresholds, the report makes policy recommendations for the period before a threshold is reached, during a threshold, and after the ecosystem has transformed.

Before a threshold is crossed, Charles said, management agencies should first and foremost support research to better identify and understand the factors that lead to ecosystem tipping points. But in the face of inevitable shifts due to climate change, managers also should improve their adaptive capacity to prepare ecosystems for the pending changes, in an effort to increase the systems' resilience to change. Management agencies should also try to reduce those ecosystem stressors that are within their control.

During a threshold event, projections can prove valuable in determining how the goods and services of an ecosystem may be affected. A threshold event is also a good time to promote institutional changes in management that will help an ecosystem adapt and survive the changes.

Once the threshold event has taken place, the obvious challenge will be adjusting to a new ecosystem; but it is also a good opportunity to look back and use the experience as a learning tool for other ecosystems. In the end, the adaptive management method is about learning, and evolving. And we have much to learn, Charles said.

"The bottom line is we really don't know a lot about thresholds," she added. The report identified important next steps, including the identification of processes and indicators of threshold change and the expansion of management approaches to regional scales, in order to match the likely scales of ecosystem change.

To read the report, which includes additional policy recommendations, visit www.climatescience.gov.

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June 9, 2009