Scientists may use different timescales when speaking ofabrupt 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 ongoinggreenhouse 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]
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 of events described asabrupt 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 onAntarctica.[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 ongoinggreenhouse 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]
Several periods of abrupt climate change have been identified in thepaleoclimatic record. Notable examples include:
About 25 climate shifts, calledDansgaard–Oeschger cycles, which have been identified in theice core record during the glacial period over the past 100,000 years.[12]
TheYounger Dryas event, notably its sudden end. It is the most recent of the Dansgaard–Oeschger cycles and began 12,800 years ago and moved back into a warm-and-wet climate regime about 11,600 years ago."Abrupt Climate Change - What scientific evidence do we have that abrupt climate change has happened before?".ocp.ldeo.columbia.edu. 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."[13] A model for this event based on disruption to thethermohaline circulation has been supported by other studies.[14]
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.[18][19] Life on land took 30 million years to recover.[20]
TheCarboniferous 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 the8.2-kiloyear event, which is associated with the draining ofGlacial Lake Agassiz.[21] Another example is theAntarctic Cold Reversal, c. 14,500 years before present (BP), which is believed to have been caused by a meltwater pulse probably from either theAntarctic ice sheet[22] or theLaurentide Ice Sheet.[23] These rapid meltwater release events have been hypothesized as a cause for Dansgaard–Oeschger cycles.[24]
A five-year study led by theOxford School of Archaeology and additionally conducted byRoyal Holloway,University of London, theOxford University Museum of Natural History, and theNational Oceanography Centre Southampton[25] completed in 2013 called "Response of Humans to Abrupt Environmental Transitions" and referred to as "RESET" aimed to see if the hypothesis that humans have major development shifts during or immediately after abrupt climate changes with the aid of knowledge pulled from research on the palaeoenvironmental conditions, prehistoric archaeological history, oceanography, and volcanic geology of the last 130,000 years and across continents.[26][27] It also aimed to predict possible human behavior in the event of climate change, and the timing of climate change.[28]
A 2017 study concluded that similar conditions to today'sAntarctic ozone hole (atmospheric circulation and hydroclimate changes), ~17,700 years ago, when stratospheric ozone depletion contributed to abrupt accelerated Southern Hemispheredeglaciation. The event coincidentally happened with an estimated 192-year series of massive volcanic eruptions, attributed toMount Takahe inWest Antarctica.[29]
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 theNorth Atlantic Ocean'sMeridional Overturning Circulation during the lastice age, affecting climate worldwide.[30]
There have also been two occasions when the Atlantic's Meridional Overturning Circulation lost a crucial safety factor. TheGreenland Sea flushing at 75 °N shut down in 1978, recovering over the next decade.[32] Then the second-largest flushing site, theLabrador Sea, shut down in 1997[33] for ten years.[34] While shutdowns overlapping in time have not been seen during the 50 years of observation, previous total shutdowns had severe worldwide climate consequences.[30]
It has been postulated that teleconnections – oceanic and atmospheric processes on different timescales – connect both hemispheres during abrupt climate change.[35]
One source of abrupt climate change effects is afeedback process, in which a warming event causes a change that adds to further warming.[37] 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 thealbedo ("whiteness") of the earth and its ability to absorb the sun's energy.[38]
Soil carbon feedback is the release of carbon from soils in response to global warming.
The probability of abrupt change for some climate related feedbacks may be low.[40][41] 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.[41]
Possibletipping elements in the climate system include regionaleffects of climate change, some of which had abrupt onset and may therefore be regarded as abrupt climate change.[42] 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".[42]
Inclimate science, atipping point is a critical threshold that, when crossed, leads to large, accelerating and often irreversible changes in theclimate system.[43] If tipping points are crossed, they are likely to have severe impacts on human society and may accelerateglobal warming.[44][45] Tipping behavior is found across the climate system, for example inice sheets,mountain glaciers,circulation patterns in the ocean, inecosystems, and the atmosphere.[45] Examples of tipping points includethawing permafrost, which will releasemethane, a powerfulgreenhouse gas, or melting ice sheets and glaciers reducing Earth'salbedo, 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.[46]
Isostatic rebound in response to glacier retreat (unloading) and increased local salinity have been attributed to increased volcanic activity at the onset of the abruptBølling–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.[47]
A summary of the path of thethermohaline circulation. Blue paths represent deep-water currents, and red paths represent surface currents.The Permian–Triassic extinction event, labelled "P–Tr" here, is the most significant extinction event in this plot for marinegenera.
In the past, abrupt climate change has likely caused wide-ranging and severe impacts as follows:
Loss of biodiversity: without interference from abrupt climate change and other extinction events, the biodiversity of Earth would continue to grow.[48]
Sea ice decline in the North Atlantic and Nordic Seas, specifically in theBaffin Bay andLabrador Sea.[49]
^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.Bibcode:2005QSRv...24..513G.doi:10.1016/j.quascirev.2004.10.016.
^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.Bibcode:2008E&PSL.268..397K.doi:10.1016/j.epsl.2008.01.032.
^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.Bibcode:2004QSRv...23....7T.doi:10.1016/j.quascirev.2003.09.004.
^"Heinrich and Dansgaard–Oeschger Events".National Centers for Environmental Information (NCEI) formerly known as National Climatic Data Center (NCDC). NOAA. Archived fromthe original on 22 December 2016. Retrieved7 August 2019.
^abMayewski, 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.Bibcode:2016EGUGA..18.2567M.
^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. Archived fromthe original on 4 October 2014. Retrieved10 May 2018.
^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.Bibcode:2015ACPD...1520059H.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.
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