Abrupt climate change

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An abrupt climate change occurs when the climate system is forced to transition to a new state at a rate that is determined by the climate system itself, and which is more rapid than the rate of change of the external forcing.^[1] Past events include the end of the Younger Dryas^[2], and Dansgaard-Oeschger events. The term is also used within the context of anthropogenic global warming to describe sudden climate change that is detectable over the time-scale of a human lifetime. One proposed reason for the observed abrupt climate change is that feedback loops within the climate system both enhance small perturbations and cause a variety of stable states.^[3]

Timescales of events described at 'abrupt' may vary dramatically. Changes recorded in the climate of Greenland at the end of the Younger Dryas, as measured by ice-cores, imply a sudden warming of +10°C within a timescale of a few years^[4]. Other abrupt changes are the +4 °C on Greenland 11 270 years ago^[5] or the abrupt +6 °C warming 22 000 years ago on Antarctica^[6]. By contrast, the Paleocene-Eocene Thermal Maximum may have initiated anywhere between a few decades and several thousand years.

[edit] Definitions

According to the Committee on Abrupt Climate Change of the National Research Council^[1][7]:

There are essentially two definitions of abrupt climate change:

• In terms of physics, it is a transition of the climate system into a different mode on a time scale that is faster than the responsible forcing.
• In terms of impacts, "an abrupt change is one that takes place so rapidly and unexpectedly that human or natural systems have difficulty adapting to it".

These definitions are complementary: the former gives some insight into how abrupt climate change comes about ; the latter explains why there is so much research devoted to it, why it inspires catastrophe movies, and may even be the reason why you are reading this page.

[edit] Current situation

The IPCC^[8] states that global warming "could lead to some effects that are abrupt or irreversible".

[edit] Risks & consequences

In an article in Science, Alley et al. said "it is conceivable that human forcing of climate change is increasing the probability of large, abrupt events. Were such an event to recur, the economic and ecological impacts could be large and potentially serious."^[9]

[edit] Regional changes

Lenton et al.^[10] investigated tipping elements in the climate system. These were regional effects of global warming, some of which had abrupt onset and may therefore be regarded as abrupt climate change. They found that "Our synthesis of present knowledge suggests that a variety of tipping elements could reach their critical point within this century under anthropogenic climate change."

[edit] Ocean effects

A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents

Global oceans have established patterns of currents. Several potential disruptions to this system of currents have been identified as a result of global warming:

• Increasing frequency of El Nino events.^[11][12]
• Potential disruption to ^[13] the thermohaline circulation, such as that which may have occurred during the Younger Dryas event.^[14]
• Changes to the North Atlantic oscillation^[15]

[edit] Climate feedback effects

One source of abrupt climate change effects is a feedback process, in which a warming event causes a change which leads to further warming. This can also apply to cooling. Example of such feedback processes are:

• Ice-albedo feedback, where the advance or retreat of ice cover alters the 'whiteness' or the earth, and its ability to absorb the sun's energy.^[16]
• The dying and burning of forests, as a result of global warming.^[17]

[edit] Past events

The Younger Dryas period of abrupt climate change is named after the Alpine flower, Dryas.

Several periods of abrupt climate change have been identified in the paleoclimatic record. Notable examples include:

• About 25 climate shifts, called Dansgaard-Oeschger cycles, which have been identified in the ice core record during the glacial period over the past 100,000 years.^{[citation needed]} The most recent of these events was the Younger Dryas which began 12,900 years ago and moved back into a warm-and-wet climate regime about 11,600 years ago.^{[citation needed]}
• The Younger Dryas event, notably its sudden end. It has been suggested that: "The extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the North Atlantic climate system."^[18] A model for this event based on disruption to the thermohaline circulation has been supported by other studies.^[19]
• The Paleocene-Eocene Thermal Maximum, timed at 55 million years ago, which may have been caused by the clathrate gun effect^[20], although potential alternative mechanisms have been identified.^[21] This was associated with rapid ocean acidification^[22]
• The Permian-Triassic Extinction Event, also known as the great dying, in which up to 95% of all species became extinct, has been hypothesized to be related to a rapid change in global climate.^[23][24]

There are also abrupt climate changes associated with the catastrophic draining of glacial lakes. One example of this is the 8.2 kiloyear event, which associated with the draining of Glacial Lake Agassiz.^[25] Another example is the Antarctic Cold Reversal, c. 14,500 years before present (BP), which is believed to have been caused by a meltwater pulse from the Antarctic ice sheet.^{[citation needed]} These rapid meltwater release events have been hypothesized as a cause for Dansgaard-Oeschger cycles,^[26]

[edit] Consequential effects

K-T

Tr-J

P-Tr

Late D

O-S

Millions of years ago

Marine extinction intensity through time. The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the "Big Five" extinction events are clickable hyperlinks; see Extinction event for more details. (source and image info)

Abrupt climate change has likely been the cause of wide ranging and severe effects:

• Rapid Ocean acidification^[27], which can harm marine life (such as corals).^[28]

This article or section may contain unpublished synthesis of published material that conveys ideas not attributable to the original sources. See the talk page for details. (May 2009)

• Mass extinctions in the past, most notably the great dying, have been suggested as a consequence of abrupt climate change.^[29]

[edit] References

[edit] Further reading

• Dessler, A.E. and Parson, E.A. The Science and Politics of Global Climate Change: A Guide to the Debate. Cambridge University Press, 0-521-53941-2, 2006.
• Alley, Richard (2000). The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future. Princeton University Press.
• Calvin, William H. (2002). A Brain for All Seasons: Human Evolution and Abrupt Climate Change. University of Chicago Press.
• Cox, John D. (2005). Climate Crash: Abrupt Climate Change and What It Means for Our Future. Washington DC: Joseph Henry Press.
• Drummond, Carl N. and Wilkinson, Bruce H. (2006) Interannual Variability in Climate Data, Journal of Geology, v. 114, p. 325-339.

[edit] External links

• Abrupt Climate Change Information from the Ocean & Climate Change Institute, Woods Hole Oceanographic Institution
• Newest reports on US EPA website