Abrupt climate change

An abrupt climate change occurs when the climate system is forced to transition to a new climate state at a rate that is determined by the climate system energy-balance, and which is more rapid than the rate of change of the external forcing.[1] Past events include the end of the Carboniferous Rainforest Collapse,[2] Younger Dryas,[3] Dansgaard-Oeschger events, Heinrich events and possibly also the Paleocene-Eocene thermal maximum.[4] The term is also used within the context of 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.[5]

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.[6] Other abrupt changes are the +4 °C (+7.2 °F) on Greenland 11,270 years ago[7] or the abrupt +6 °C (11 °F) warming 22,000 years ago on Antarctica.[8] By contrast, the Paleocene-Eocene thermal maximum may have initiated anywhere between a few decades and several thousand years. Finally, Earth Systems 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, affecting over 3 billion people and most places of great species diversity on Earth.[9]

Definitions

According to the Committee on Abrupt Climate Change of the National Research Council:[1][10]

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.

Current situation

The IPCC states that global warming "could lead to some effects that are abrupt or irreversible".[11]

In an article in Science, Richard 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."[12]

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—in human infrastructure and ecosystems for example—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.[13]

Regional changes

Lenton et al.[14] 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."

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:

Effects on weather

Hansen et al. 2015 found, that the shutdown or substantial slowdown of the Atlantic Meridional Overturning Circulation (AMOC), besides possibly contributing to extreme end-Eemian events, will cause a more general increase of severe weather. Additional surface cooling from ice melt increases surface and lower tropospheric temperature gradients, and causes in model simulations a large increase of mid-latitude eddy energy throughout the midlatitude troposphere. This in turn leads to an increase of baroclinicity produced by stronger temperature gradients, which provides energy for more severe weather events.

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.

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.[20]

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:

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:

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.[30] 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. These rapid meltwater release events have been hypothesized as a cause for Dansgaard-Oeschger cycles,[31]

Abrupt climate shifts since 1976

Had the 1997 El Niño lasted twice as long, the rain forests of the Amazon basin and Southeast Asia could have quickly added much additional carbon dioxide to the air from burning and rotting,[32] with heat waves and extreme weather quickly felt around the world (The "Burn Locally, Crash Globally" scenario.[33])

Most abrupt climate shifts, however, 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.[12] But there have been a series of less dramatic abrupt climate shifts since 1976, along with some near misses.

This makes abrupt climate shifts more like a heart attack than like a chronic disease whose course can be extrapolated.[33] Like heart attacks, some abrupt climate shifts are minor, some are catastrophic—and one cannot predict which or when. The recent track record, however, is that there have been several sudden shifts and several near-misses in each decade since 1976.

Consequential effects

Extinction intensity.svg Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene
Marine extinction intensity during the Phanerozoic
%
Millions of years ago
Extinction intensity.svg Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene
The Permian–Triassic extinction event, labelled "P-Tr" here, is the most significant extinction event in this plot for marine genera.

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

See also

References

  1. 1 2 Committee on Abrupt Climate Change, National Research Council. (2002). "Definition of Abrupt Climate Change". Abrupt climate change : inevitable surprises. Washington, D.C.: National Academy Press. ISBN 978-0-309-07434-6.
  2. 1 2 3 Sahney, S.; Benton, M.J.; Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology. 38 (12): 1079–1082. Bibcode:2010Geo....38.1079S. doi:10.1130/G31182.1.
  3. ↑ Broecker, W. S. (May 2006). "Geology. Was the Younger Dryas triggered by a flood?". Science. 312 (5777): 1146–1148. doi:10.1126/science.1123253. ISSN 0036-8075. PMID 16728622.
  4. ↑ Committee on Abrupt Climate Change, Ocean Studies Board, Polar Research Board, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, National Research Council. (2002). Abrupt climate change : inevitable surprises. Washington, D.C.: National Academy Press. p. 108. ISBN 0-309-07434-7.
  5. ↑ Rial, J. A.; Pielke Sr., R. A.; Beniston, M.; Claussen, M.; Canadell, J.; Cox, P.; Held, H.; De Noblet-Ducoudré, N.; Prinn, R.; Reynolds, J. F.; Salas, J. D. (2004). "Nonlinearities, Feedbacks and Critical Thresholds within the Earth's Climate System" (PDF). Climatic Change. 65: 11–00. doi:10.1023/B:CLIM.0000037493.89489.3f.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ Mora, C (2013). "The projected timing of climate departure from recent variability". Nature. 502: 183–187. Bibcode:2013Natur.502..183M. doi:10.1038/nature12540.
  10. ↑ Harunur Rashid; Leonid Polyak; Ellen Mosley-Thompson (2011). "Abrupt climate change: mechanisms, patterns, and impacts". American Geophysical Union. ISBN 9780875904849. Retrieved 2013-09-17.
  11. ↑ "Summary for Policymakers". Climate Change 2007: Synthesis Report (PDF). IPCC. 17 November 2007.
  12. 1 2 3 Alley, R. B.; Marotzke, J.; Nordhaus, W. D.; Overpeck, J. T.; Peteet, D. M.; Pielke Jr, R. A.; Pierrehumbert, R. T.; Rhines, P. B.; Stocker, T. F.; Talley, L. D.; Wallace, J. M. (Mar 2003). "Abrupt Climate Change" (PDF). Science. 299 (5615): 2005–2010. Bibcode:2003Sci...299.2005A. doi:10.1126/science.1081056. PMID 12663908.
  13. ↑ http://dels.nas.edu/Report/Report/18373
  14. ↑ Lenton, T. M.; Held, H.; Kriegler, E.; Hall, J. W.; Lucht, W.; Rahmstorf, S.; Schellnhuber, H. J. (2008). "Inaugural Article: Tipping elements in the Earth's climate system". Proceedings of the National Academy of Sciences. 105 (6): 1786. Bibcode:2008PNAS..105.1786L. doi:10.1073/pnas.0705414105.
  15. ↑ Trenberth, K. E.; Hoar, T. J. (1997). "El Niño and climate change" (PDF). Geophysical Research Letters. 24 (23): 3057–3060. Bibcode:1997GeoRL..24.3057T. doi:10.1029/97GL03092.
  16. ↑ Meehl, G. A.; Washington, W. M. (1996). "El Niño-like climate change in a model with increased atmospheric CO2 concentrations". Nature. 382 (6586): 56–60. Bibcode:1996Natur.382...56M. doi:10.1038/382056a0.
  17. ↑ Broecker, W. S. (1997). "Thermohaline Circulation, the Achilles Heel of Our Climate System: Will Man-Made CO2 Upset the Current Balance?" (PDF). Science. 278 (5343): 1582–1588. Bibcode:1997Sci...278.1582B. doi:10.1126/science.278.5343.1582. Archived from the original (PDF) on 22 November 2009.
  18. 1 2 Manabe, S.; Stouffer, R. J. (1995). "Simulation of abrupt climate change induced by freshwater input to the North Atlantic Ocean" (PDF). Nature. 378 (6553): 165. Bibcode:1995Natur.378..165M. doi:10.1038/378165a0.
  19. ↑ Beniston, M.; Jungo, P. (2002). "Shifts in the distributions of pressure, temperature and moisture and changes in the typical weather patterns in the Alpine region in response to the behavior of the North Atlantic Oscillation" (PDF). Theoretical and Applied Climatology. 71 (1–2): 29–42. Bibcode:2002ThApC..71...29B. doi:10.1007/s704-002-8206-7.
  20. ↑ J. Hansen, M. Sato, P. Hearty, R. Ruedy, M. Kelley, V. Masson-Delmotte, G. Russell, G. Tselioudis, J. Cao, E. Rignot, I. Velicogna, E. Kandiano, K. von Schuckmann, P. Kharecha, A. N. Legrande, M. Bauer, and K.-W. Lo (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". doi:10.5194/acpd-15-20059-2015.
  21. ↑ Comiso, J. C. (2002). "A rapidly declining perennial sea ice cover in the Arctic" (PDF). Geophysical Research Letters. 29 (20): 17–11–11–4. Bibcode:2002GeoRL..29t..17C. doi:10.1029/2002GL015650.
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