Abrupt Climate Change

Abrupt Climate Change

Return to Learn About the Issues
In 2002, Richard Alley chaired a panel convened by the National Academy of Sciences, the nation’s leading source of objective advice to Congress and successive Administrations, which wrote the “Abrupt Climate Change: Inevitable Surprises” report. Here’s what Richard said in his Preface. It provides background to the rather less academic “bungy jumping off the climate roller coaster” sequence seen in ETOM program 2, POWERING THE PLANET.


Large, abrupt climate changes have repeatedly affected much or all of the Earth, locally reaching as much as 10°C change in 10 years. Available evidence suggests that abrupt climate changes are not only possible but likely in the future, potentially with large impacts on ecosystems and societies.

The report does not focus on large, abrupt causes—nuclear wars or giant meteorite impacts—but rather on the surprising new findings that abrupt climate change can occur when gradual causes push the Earth system across a threshold. Just as the slowly increasing pressure of a finger eventually flips a switch and turns on a light, the slow effects of drifting continents or wobbling orbits or changing atmospheric composition may “switch” the climate to a new state. And, just as a moving hand is more likely than a stationary one to encounter and flip a switch, faster Earth-system changes—whether natural or human-caused—are likely to increase the probability of encountering a threshold that triggers a still faster climate shift.

We do not yet understand abrupt climate changes well enough to predict them. The models used to project future climate changes and their impacts are not especially good at simulating the size, speed, and extent of the past changes, casting uncertainties on assessments of potential future changes. Thus...

...it is likely that climate surprises await us.

When orbital wiggles and rising greenhouse gases warmed the Earth from the last ice age, proxy records show that smooth changes were interspersed with abrupt coolings and warmings, wettings and dryings. By analogy, the expected future warming may come smoothly, but may come with jumps, short-lived or local coolings, floods or droughts, and other unexpected changes. Societies and ecosystems have an easier time dealing with slower or better-anticipated changes, so the abruptness and unpredictability of the possible changes may be disquieting.

...The potentially large impacts and prediction difficulties focus special attention on increasing the adaptability and resiliency of societies and ecosystems. The committee notes that...

...there is no need to be fatalistic; human and natural systems have survived many abrupt changes in the past, and will continue to do so. Nonetheless, future dislocations can be minimized by taking steps to face the potential for abrupt climate change.

The committee believes that increased knowledge is the best way to improve the effectiveness of response, and thus that research on abrupt climate change can help reduce vulnerabilities and increase adaptive capabilities.

...I hope that the readers of this report join us in seeing not peril but opportunity for improved knowledge leading toward a happier and more secure future.

Richard B. Alley, Chair Committee On Abrupt Climate Change

The body of the Report itself continues, in part:

Recent scientific evidence shows that major and widespread climate changes have occurred with startling speed. For example, roughly half the north Atlantic warming since the last ice age was achieved in only a decade, and it was accompanied by significant climatic changes across most of the globe. Similar events, including local warmings as large as 16°C, occurred repeatedly during the slide into and climb out of the last ice age.

Human civilizations arose after those extreme, global ice-age climate jumps. Severe droughts and other regional climate events during the current warm period have shown similar tendencies of abrupt onset and great persistence, often with adverse effects on societies.

Abrupt climate changes were especially common when the climate system was being forced to change most rapidly. Thus, greenhouse warming and other human alterations of the earth system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events. The abrupt changes of the past are not fully explained yet, and climate models typically underestimate the size, speed, and extent of those changes. Hence, future abrupt changes cannot be predicted with confidence, and climate surprises are to be expected.

The new paradigm of an abruptly changing climatic system has been well established by research over the last decade, but this new thinking is little known and scarcely appreciated in the wider community of natural and social scientists and policy-makers.

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

Societies have faced both gradual and abrupt climate changes for millennia and have learned to adapt through various mechanisms, such as moving indoors, developing irrigation for crops, and migrating away from inhospitable regions. Nevertheless, because climate change will likely continue in the coming decades, denying the likelihood or downplaying the relevance of past abrupt events could be costly. Societies can take steps to face the potential for abrupt climate change. The committee believes that increased knowledge is the best way to improve the effectiveness of response, and thus that research into the causes, patterns, and likelihood of abrupt climate change can help reduce vulnerabilities and increase our adaptive capabilities.

ETOM: One of the Committee’s recommendations was for research on what it called “No Regrets” approaches to adaptation and mitigation.

Recommendation 5:

Research should be undertaken to identify “no-regrets” measures to reduce vulnerabilities and increase adaptive capacity at little or no cost. No-regrets measures may include low-cost steps to:

  • slow climate change;
  • improve climate forecasting;
  • slow biodiversity loss;
  • improve water, land, and air quality;
  • and develop institutions that are more robust to major disruptions.

Technological changes may increase the adaptability and resiliency of market and ecological systems faced by the prospect of damaging abrupt climate change. Research is particularly needed to assist poor countries, which lack both scientific resources and economic infrastructure to reduce their vulnerabilities to potential abrupt climate changes. Social and ecological systems have long dealt with climate variability by taking steps to reduce vulnerability to its effects. The rapidity of abrupt climate change makes adaptation more difficult. By moving research and policy in directions that will increase the adaptability of economic and ecological systems, it might be possible to reduce vulnerability and increase adaptation at little or no cost. Many current policies and practices are likely to be inadequate in a world of rapid and unforeseen climatic changes. Improving these policies will be beneficial even if abrupt climate change turns out to fit a best-case, rather than a worst-case, scenario.

Societies will have “no regrets” about the new policies, because they will be good policies regardless of the magnitude of environmental change.

For example, the phase out of chloroflourocarbons and replacement by gases with shorter atmospheric lifetimes have reduced the US contribution to global warming while at the same time reducing future health risks posed by ozone depletion. In land-use and coastal planning, managers should consider the effects on ecosystem services that could result from interaction of abrupt climate changes with changes caused by people.

...Because of the strength of existing infrastructure and institutions, the United States and other wealthy nations are likely to cope with the effects of abrupt climate change more easily than poorer countries. That does not mean that developed countries can remain isolated from the rest of the world, however. With growing globalization, adverse impacts—although likely to vary from region to region because exposure and sensitivity will vary—are likely to spill across national boundaries, through human and biotic migration, economic shocks, and political aftershocks. Thus, even though this report focuses primarily on the United States, the issues are global and it will be important to give attention to the issues faced by poorer countries that are likely to be especially vulnerable to the social and economic impacts of abrupt climate change.

The United States is uniquely positioned to provide both scientific and financial leadership, and to work collaboratively with scientists around the world, to gain better understanding of the global impacts of abrupt climate change as well as reducing the vulnerability and increasing the adaptation in countries that are particularly vulnerable to these changes.

Many of the recommendations in this report, although currently aimed at US institutions, would apply throughout the world.

For more form Richard on this topic, please see:

Abrupt Climate Change; November 2004; Scientific American Magazine; by Richard B. Alley; 8 Page(s)

In the Hollywood disaster thriller The Day after Tomorrow, a climate catastrophe of ice age proportions catches the world unprepared. Millions of North Americans flee to sunny Mexico as wolves stalk the last few people huddled in freeze-dried New York City. Tornadoes ravage California. Giant hailstones pound Tokyo. Are overwhelmingly abrupt climate changes likely to happen anytime soon, or did Fox Studios exaggerate wildly? The answer to both questions appears to be yes. Most climate experts agree that we need not fear a full-fledged ice age in the coming decades. But sudden, dramatic climate changes have struck many times in the past, and they could happen again. In fact, they are probably inevitable.

And, Richard’s previous book, “The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future”

Copyright © National Academy of Sciences. All rights reserved. Abrupt Climate Change: Inevitable Surprises http://www.nap.edu/catalog/10136.html vi PREFACE

Watch and share

Check out episodes, clips, and video content that feature everyday Earth Operators in action.

Don't wait do
something now

Ready to reduce your own footprint? Find out how saving energy = saving money.

Energize your community

Changing the planet starts with you, but doesn’t end there. Find out how you can bring clean energy to your community.