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A Final Word

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The Norwegian Sea. Image from NASA.

The study of abrupt change is still in its infancy; while new data are published every month, the paleo record is still incomplete. Additional high-resolution, well-dated proxy records are needed from around the globe to fill in gaps in our understanding. As definitions of abrupt change are being refined, scientists continue to pose hypotheses regarding mechanisms, but only a few of these mechanisms have been tested using climate models. Even for one of the best known abrupt change events, the Younger Dryas, neither the global extent of temperature or precipitation change nor the accompanying changes in ocean circulation and atmospheric trace gases are well known. The next decade is sure to bring many new developments on this topic.

Even from the proxy data that exist, one thing is relatively certain: our climate system is not always well-behaved. It can, and often does, change in surprising ways. Positive feedbacks are a key ingredient for this behavior, amplifying a small change or perturbation in the climate system. Paleo records also show that abrupt changes happen during both glacial and interglacial periods, although they may take on different characteristics when large ice sheets exist on Earth. During the Holocene, for example, regional-scale droughts have been very important, while weakening of the meridional overturning circulation had consequences on the hemispheric-to-global scale during the last glacial period.

The perspective of the paleo record suggests that future climate change will also contain some surprises. Currently, global mean temperature is rising due to emissions of greenhouse gases by humans (see the Paleo Perspective on Global Warming). It is possible that this climate perturbation will be amplified by some of the positive feedbacks that operated during past abrupt events. The Arctic, for example, might become a locus of abrupt change due to the ice-albedo feedback (Holland et al., 2006).

Should I Worry?

It is important not to be fatalistic about the threats posed by abrupt climate change.

(National Research Council, 2002)

At this point, we know that abrupt climate change is a reality. It has happened before and will happen again. How and why it happened in the past are still open questions, as are how, why, and when it might happen in the future. The information found in natural archives of climate and environmental change such as ice cores, lake and ocean sediments, tree rings, and other proxies can be of profound benefit to society in understanding and predicting future climate change.

The goal of the World Data Center for Paleoclimatology is to provide easy access to high quality scientific information derived from rigorous studies of past climate changes. We believe, as do most climate scientists, that the topic of abrupt climate change is worthy of further study, and needs more information before predictions can be made about future events. Several national and international initiatives, such as the U.S. Climate Change Science Plan, have targeted this topic as a priority for scientific research.

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