Scientists may use different timescales when speaking of abrupt events. For example, the duration of the onset of the Paleocene–Eocene Thermal Maximum may have been anywhere between a few decades and several thousand years. In comparison,
climate models predict that under ongoing
greenhouse gas emissions, the Earth's near surface temperature could depart from the usual range of variability in the last 150 years as early as 2047.[7]
Definitions
Abrupt climate change can be defined in terms of physics or in terms of impacts: "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."[8]
Timescales
Timescales of events described as 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 (+18 °F) within a timescale of a few years.[9] Other abrupt changes are the +4 °C (+7.2 °F) on Greenland 11,270 years ago[10] or the abrupt +6 °C (11 °F) warming 22,000 years ago on
Antarctica.[11]
By contrast, the Paleocene–Eocene Thermal Maximum may have initiated anywhere between a few decades and several thousand years. Finally,
Earth System's models project that under ongoing
greenhouse gas emissions as early as 2047, the Earth's near surface temperature could depart from the range of variability in the last 150 years.[7]
General
Possible
tipping elements in the climate system include regional
effects of climate change, some of which had abrupt onset and may therefore be regarded as abrupt climate change.[12] Scientists have stated, "Our synthesis of present knowledge suggests that a variety of tipping elements could reach their critical point within this century under anthropogenic climate change".[12]
It has been postulated that teleconnections – oceanic and atmospheric processes on different timescales – connect both hemispheres during abrupt climate change.[13]
A 2013 report from the U.S.
National Research Council called for attention to the abrupt impacts of climate change, stating that even steady, gradual change in the physical climate system can have abrupt impacts elsewhere, such as in human infrastructure and ecosystems if critical thresholds are crossed. The report emphasizes the need for an early warning system that could help society better anticipate sudden changes and emerging impacts.[14]
A characteristic of the abrupt climate change impacts is that they occur at a rate that is faster than anticipated. This element makes ecosystems that are immobile and limited in their capacity to respond to abrupt changes, such as forestry ecosystems, particularly vulnerable.[15]
The probability of abrupt change for some climate related feedbacks may be low.[16][17] Factors that may increase the probability of abrupt climate change include higher magnitudes of global warming, warming that occurs more rapidly and warming that is sustained over longer time periods.[17]
Climate models are currently[when?] unable to predict abrupt climate change events, or most of the past abrupt climate shifts.[18] A potential abrupt feedback due to
thermokarst lake formations in the Arctic, in response to thawing
permafrost soils, releasing additional greenhouse gas methane, is currently not accounted for in climate models.[19]
Effects
In the past, abrupt climate change has likely caused wide-ranging and severe effects as follows:
Loss of biodiversity: without interference from abrupt climate change and other extinction events, the biodiversity of Earth would continue to grow.[22]
In
climate science, a
tipping point is a critical threshold that, when crossed, leads to large, accelerating and often irreversible changes in the
climate system.[31] If tipping points are crossed, they are likely to have severe impacts on human society and may accelerate
global warming.[32][33] Tipping behavior is found across the climate system, for example in
ice sheets,
mountain glaciers,
circulation patterns in the ocean, in
ecosystems, and the atmosphere.[33] Examples of tipping points include
thawing permafrost, which will release
methane, a powerful
greenhouse gas, or melting ice sheets and glaciers reducing Earth's
albedo, which would warm the planet faster. Thawing permafrost is a threat multiplier because it holds roughly twice as much carbon as the amount currently circulating in the atmosphere.[34]
Tipping points are often, but not necessarily, abrupt. For example, with average global warming somewhere between 0.8 °C (1.4 °F) and 3 °C (5.4 °F), the
Greenland ice sheet passes a tipping point and is doomed, but its melt would take place over millennia.[30][35] Tipping points are possible at today's global warming of just over 1 °C (1.8 °F) above
preindustrial times, and highly probable above 2 °C (3.6 °F) of global warming.[33] It is possible that some tipping points are close to being crossed or have already been crossed, like those of the
West Antarctic and
Greenland ice sheets, the
Amazon rainforest and
warm-water coral reefs.[36]
A danger is that if the tipping point in one system is crossed, this could cause a cascade of other tipping points, leading to severe,
potentially catastrophic,[37] impacts.[38] Crossing a threshold in one part of the climate system may trigger another tipping element to tip into a new state.[39] For example, ice loss in West Antarctica and Greenland will significantly alter
ocean circulation. Sustained warming of the northern high latitudes as a result of this process could activate tipping elements in that region, such as permafrost degradation, and boreal
forest dieback.[31]
Scientists have identified many elements in the climate system which may have tipping points.[40][41] As of September 2022, nine global core tipping elements and seven regional impact tipping elements are known.[30] Out of those, one regional and three global climate elements will likely pass a tipping point if global warming reaches 1.5 °C (2.7 °F). They are the Greenland ice sheet collapse, West Antarctic ice sheet collapse, tropical coral reef die off, and boreal permafrost abrupt thaw.
Tipping points exists in a range of systems, for example in the
cryosphere, within ocean currents, and in terrestrial systems. The tipping points in the cryosphere include: Greenland ice sheet disintegration, West Antarctic ice sheet disintegration,
East Antarctic ice sheet disintegration, arctic sea ice decline,
retreat of mountain glaciers, permafrost thaw. The tipping points for ocean current changes include the
Atlantic Meridional Overturning Circulation (AMOC), the
North Subpolar Gyre and the
Southern Ocean overturning circulation. Lastly, the tipping points in terrestrial systems include Amazon rainforest dieback, boreal forest biome shift, Sahel greening, and vulnerable stores of tropical peat carbon.
Past events
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.[42]
The
Younger Dryas event, notably its sudden end. It is the most recent of the Dansgaard–Oeschger cycles and began 12,900 years ago and moved back into a warm-and-wet climate regime about 11,600 years ago.[citation needed] 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."[43] A model for this event based on disruption to the
thermohaline circulation has been supported by other studies.[26]
The Permian–Triassic Extinction Event, in which up to 95% of all species became extinct, has been hypothesized to be related to a rapid change in global climate.[47][21] Life on land took 30 million years to recover.[20]
The
Carboniferous Rainforest Collapse occurred 300 million years ago, at which time tropical rainforests were devastated by climate change. The cooler, drier climate had a severe effect on the biodiversity of amphibians, the primary form of vertebrate life on land.[3]
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 is associated with the draining of
Glacial Lake Agassiz.[48] 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 probably from either the
Antarctic ice sheet[49] or the
Laurentide Ice Sheet.[50] These rapid meltwater release events have been hypothesized as a cause for Dansgaard–Oeschger cycles,[51]
A 2017 study concluded that similar conditions to today's
Antarctic ozone hole (atmospheric circulation and hydroclimate changes), ~17,700 years ago, when stratospheric ozone depletion contributed to abrupt accelerated Southern Hemisphere
deglaciation. The event coincidentally happened with an estimated 192-year series of massive volcanic eruptions, attributed to
Mount Takahe in
West Antarctica.[52]
Possible precursors
Most abrupt climate shifts are likely due to sudden circulation shifts, analogous to a flood cutting a new river channel. The best-known examples are the several dozen shutdowns of the
North Atlantic Ocean's
Meridional Overturning Circulation during the last
ice age, affecting climate worldwide.[53]
There have also been two occasions when the Atlantic's Meridional Overturning Circulation lost a crucial safety factor. The
Greenland Sea flushing at 75 °N shut down in 1978, recovering over the next decade.[54] Then the second-largest flushing site, the
Labrador Sea, shut down in 1997[55] for ten years.[56] While shutdowns overlapping in time have not been seen during the 50 years of observation, previous total shutdowns had severe worldwide climate consequences.[53]
One source of abrupt climate change effects is a
feedback process, in which a warming event causes a change that adds to further warming.[58] The same can apply to cooling. Examples of such feedback processes are:
Ice–albedo feedback in which the advance or retreat of ice cover alters the
albedo ("whiteness") of the earth and its ability to absorb the sun's energy.[59]
Soil carbon feedback is the release of carbon from soils in response to global warming.
Isostatic rebound in response to glacier retreat (unloading) and increased local salinity have been attributed to increased volcanic activity at the onset of the abrupt
Bølling–Allerød warming. They are associated with the interval of intense volcanic activity, hinting at an interaction between climate and volcanism: enhanced short-term melting of glaciers, possibly via albedo changes from particle fallout on glacier surfaces.[61]
^Grachev, A.M.; Severinghaus, J.P. (2005). "A revised +10±4 °C magnitude of the abrupt change in Greenland temperature at the Younger Dryas termination using published GISP2 gas isotope data and air thermal diffusion constants". Quaternary Science Reviews. 24 (5–6): 513–9.
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^Kobashi, T.; Severinghaus, J.P.; Barnola, J. (30 April 2008). "4 ± 1.5 °C abrupt warming 11,270 yr ago identified from trapped air in Greenland ice". Earth and Planetary Science Letters. 268 (3–4): 397–407.
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^Taylor, K.C.; White, J; Severinghaus, J; Brook, E; Mayewski, P; Alley, R; Steig, E; Spencer, M; Meyerson, E; Meese, D; Lamorey, G; Grachev, A; Gow, A; Barnett, B (January 2004). "Abrupt climate change around 22 ka on the Siple Coast of Antarctica". Quaternary Science Reviews. 23 (1–2): 7–15.
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Clark, P.U.; et al. (December 2008).
"Executive Summary". Abrupt Climate Change. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Reston, Virginia: U.S. Geological Survey. pp. 1–7.
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abcMayewski, Paul Andrew (2016). "Abrupt climate change: Past, present and the search for precursors as an aid to predicting events in the future (Hans Oeschger Medal Lecture)". EGU General Assembly Conference Abstracts. 18: EPSC2016-2567.
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^J. Hansen; M. Sato; P. Hearty; R. Ruedy; et al. (2015).
"Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous". Atmospheric Chemistry and Physics Discussions. 15 (14): 20059–20179.
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doi:10.5194/acpd-15-20059-2015. Our results at least imply that strong cooling in the North Atlantic from AMOC shutdown does create higher wind speed. * * * The increment in seasonal mean wind speed of the northeasterlies relative to preindustrial conditions is as much as 10–20%. Such a percentage increase of wind speed in a storm translates into an increase of storm power dissipation by a factor ~1.4–2, because wind power dissipation is proportional to the cube of wind speed. However, our simulated changes refer to seasonal mean winds averaged over large grid-boxes, not individual storms.* * * Many of the most memorable and devastating storms in eastern North America and western Europe, popularly known as superstorms, have been winter cyclonic storms, though sometimes occurring in late fall or early spring, that generate near-hurricane-force winds and often large amounts of snowfall. Continued warming of low latitude oceans in coming decades will provide more water vapor to strengthen such storms. If this tropical warming is combined with a cooler North Atlantic Ocean from AMOC slowdown and an increase in midlatitude eddy energy, we can anticipate more severe baroclinic storms.
^"Heinrich and Dansgaard–Oeschger Events". National Centers for Environmental Information (NCEI) formerly known as National Climatic Data Center (NCDC). NOAA. Archived from
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