Abrupt Climate Change Tipping Elements in the Earth’s Climate System -Lenton et al. (2008) Abrupt Tropical Climate Change: Past and Present -Thompson et al. (2006) Seth T. Warthen Graduate Student – ASP The Ohio State University Geography 5921 Overview / Outline • Meet the Authors • Review the Lenton et al. (2008) paper • Review the Thompson et al. (2006) paper • Overall conclusions The Faces Behind the Science Dr. Tim Lenton • Prof. at University of Exeter • BA from U. Cambridge • PhD from U. of East Anglia Dr. Lonnie Thompson • Prof. at the Ohio State University (BPRC) • BS from Marshall University • MS and PhD from OSU • CV has two pages of awards (65 pages total) What’s actually “abrupt”? • Lenton et al. (2008): —“when the climate system is forced to cross some threshold, triggering a transition to a new state at a rate determined by the climate system itself and faster than the cause” • Societal or ecological definition: —“A climatic change that takes place so rapidly and unexpectedly that human and natural systems have difficulty adapting to it” What’s this “tipping point” you mentioned? • Tipping Point: – The critical point at which the climate system is altered • Tipping Element: – The portion of the climate system that when altered can push beyond the tipping point The canoe analogy • Tipping Element: – The portion of the climate system that when altered can push beyond the tipping point The canoe analogy • Tipping Point: – The critical point at which the climate system is altered The canoe analogy • The result: – No easy way back – Fun for the whole family! Policy-relevant tipping elements • Tipping elements relevant to this century —Decisions relating to element must be within a “political time horizon” —Time to observe change plus time to trigger it lie within “ethical time horizon” —A significant amount of people care about the fate of the element Ranking the threat • High sensitivity / smallest uncertainty: – Greenland Ice Sheet, Arctic sea-ice • Intermediate sensitivity / largest uncertainty: – West Antarctic Ice Sheet, boreal forests, Amazon rainforest, ENSO, West African monsoon • Low sensitivity / intermediate uncertainty – Thermohaline Circulation An early warning • Anticipating the bifurcation (tipping point): – Uses “degenerate fingerprinting” › Reconstruct t (tau) characteristic of threshold through time series analysis › Use in intermediate complexity model Lenton et al. (2008) Conclusions • Tipping Points: – Further work may make it possible to create “early warnings” for some tipping points • Tipping Elements: – There are numerous tipping elements (WAIS, GIS, THC, ENSO, etc.) that have various (and dire) impacts on climate › Varying time scales and “abruptness” › Some well within IPCC projected warming for this century – Climate is very complex… likely more tipping elements yet to be discovered Thompson et al. (2006) Abrupt tropical climate change Thompson et al. background • Tropical / Low-latitude Glaciers: – Used δ18O from glacial ice cores as a proxy to examine temperature fluctuations in the tropics – Used 14C dating or organic material • Goal: ‒ Figure out if parallels between the current climate and glacial retreat exist with those of the past ‒ Are the dynamics of tropical glaciers changing? Unprecedented glacial retreat The last 400 years (in 5-yr averages) • Accumulation (An): – Only Quelccaya usable in Peruvian Andes › Other sites had rapidly thinning layers – Dasuopu has record somewhat inverse to others › Is located in Himalayas (monsoon-dominated) where the others are located on Tibetan Plateau (westerlies-dominated) • Temperature (δ18O ): ‒ Low-latitude sites show similarities, but: › Warming starts earlier in Tibetan Plateau › Huascaran shows earliest Andean warming (closest to equator), Sajama shows little trend (furthest south, very dry) • Composites ‒ Show δ18O depletion (cooling) through Little Ice age, δ18O enrichment (warming) in current warp period ‒ Greatest δ18O depletion 1810-1820 › Unknown volcanic eruption in 1809, Tambora eruption in 1815 The last 2000 years (decadal Averages) • Mostly Good agreement in Climatic period timings: ‒ MWP (~900-1300 A.D.) ‒ LIA (~1400-1800 A.D.) ‒ CWP (~1850 A.D. -present) – MWP and LIA not really seen in Tibetan Plateau composite, but all show anomalous δ18O enrichment in recent centuries › Signifies change in dynamics of high altitude tropical glaciers, regardless of if δ18O correlated with temp or precip › Spatially homogeneous nature of temperature gradient (compared to other atmospheric variables) suggest it’s the primarily responsible for glacial retreat Don’t get caught with your plants down… In case we needed more evidence… • Glacial retreat reveals hidden secrets: ‒ Distichia muscoides (plant) recovered from Quelccaya was 14C dated to around 5100 y. old › Implies temperatures in this region haven’t been this warm since early Holocene › Level of glacial retreat is unprecedented for last 5000 years ‒ Preserved Tyrolean “Ice Man” recovered from Alps, 14C dated to 5050-5350 years old • 5k Event - An abrupt cold snap indicated by: ‒ Recovery and carbon dating of previously frozen specimens ‒ Marine records indicate spike in terrigenous material ‒ Other fossil, artifact, and proxy evidence Thompson et al. (2006) Conclusions • Tropical glacial retreat: – Recent accelerating retreat of glaciers unprecedented for at least previous 25 millennia – Retreat likely linked with the current warm period – Anthropogenic forcing has interrupted the cooling of the late Holocene, pushing us to a climate closer to that of 5000 years ago – “May signal that the climate system has exceeded a critical threshold, and that most low-latitude, high-altitude glaciers are likely to disappear in the near future” Overall Conclusions • The Climate can, has, and will change: – Abrupt changes in climate aren’t overly uncommon on a geologic timescale › Dansgaard-Oeschger events, 5k event, volcanic eruptions, etc. – Glaciers are retreating on a level unseen for 5000 years – There exist tipping points and tipping elements › Glaciers may be an example of a tipping element reaching a tipping point › We may be able to predict these tipping points – Climate is very complex Further Work? • The rise of the model: – Increased computing power leads to more powerful climate models – More paleoproxies: – The more proxies we have to examine the climate of the past, the more we can understand about the current/future – More analogues! – Geoengineering: – Definitely not a “best case” scenario, but the way things are progressing now… References / Questions? “Ice asks no questions, presents no arguments, reads no newspapers listens to no debates. It is not burdened by ideology and carries no political baggage as it changes from solid to liquid. It just melts.” -From A World Without Ice by Henry Pollack, 2009 Alley R. B. and Coauthors, 2003: Abrupt Climate Change. Science, 299, 2005-2010, doi:10.1126/science.1081056. Lenton T. M., H. Held, E. Kriegler, J. W. Hall, W. Lucht, S. Rahmstorf, and H. J. Schellnhuber, 2008: Tipping elements in the Earth’s climate system. Proc. Natl. Acad. Sci., 105, 17861793, doi:10.1073/pnas.0705414105. Lenton T. M.: Early warning of climate tipping points. Nature Climate Change, 1, 201-209, doi:10.1038/NCLIMATE1143 Thompson L. G. and Coauthors, 2006: Abrupt tropical climate change: Past and present. Proc. Natl. Acad. Sci., 103, 10536-10543, doi:10.1073/pnas.0603900103.