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Is there a credible upper bound for global sea level rise and can we live with it? Chaos in a changing climate Chaos and Complex Systems Seminar UW-Madison, January 27, 2009 Philip Keillor [email protected] Differing perceptions of chaos • “Chaos is the score upon which reality is written.” • …Henry Miller, American writer “Reality is the score upon which chaos is written.” …Philip Keillor, American coastal engineer My intent for this seminar • 1. talk about chaos in the climate system…and abrupt climate change • 2. focus on some chaotic elements that may affect sea level rise • 3. show you a wish list for recommendations on extreme sea level rise View of a climate modeler: • “Climate can vary chaotically, i.e., in the absence of any forcing. Indeed, the climate system exemplifies ‘complexity’, a combination of deterministic behavior and unpredictable variations (‘noise’ or ‘chaos’) • Hansen et al, 1997 Hansen, et al 1997 Hansen et al, 1997 Comparison of observed and modeled climate change: 1979-1996 (Hansen et al, 1997): • “Observed climate changes contained unambiguous signatures of both natural and anthropogenic climate forcings.” • “Year-to-year climate changes at middle latitudes…are primarily chaotic functions.” Abrupt Climate Change (NRC 2002) “…when the climate system is forced to cross some threshold, triggering a transition to a new stat at a rate determined by the climate system itself and faster than the cause.” • “…one that takes place so rapidly and unexpectedly that human or natural systems have difficulty adapting to it.” Abrupt Climate Change (NRC 2002) • “…surprising new findings that abrupt climate change can occur when gradual causes push the earth system across a threshold” • “Chaotic processes in the climate system may allow the cause of such an abrupt climate change to be undetectably small.” A brand new definition of abrupt climate change (USCCP 2008): • “A large scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades and causes substantial disruptions in human and natural systems.” Dangerous climate change gets public attention • Feb. 2005. U.K. DEFRA’s International Symposium on Stabilisation of Greenhouse Gas Concentrations, Avoiding Dangerous Climate Change • July 2005. Tony Blair’s main agenda item at G8 Summit. • May 2006. David Attenborough hosted a two part series; “Climate Chaos” on the BBC • 2006. Al Gore’s widely-acclaimed documentary and book: Inconvenient Truth Chaos Found in IPCC 2007 • • • • • • nonlinearities, climate feedbacks, internal climate variability, tipping points, thresholds, possibilities of abrupt climate changes Some places to look for chaos in climate changes • • • • • 1. hydrologic cycle 2. flow of the Gulf Stream 3. release of trapped methane 4. ecosystem changes 5. human systems changes More places to look for chaos in climate changes • • • • • • 6. the global carbon cycle 7. clouds 8. aerosols 9. ocean wind patterns and currents 10. rapid polar glacier melting 11. changes in albedo A bottom line on climate feedbacks: • “The large response of the climate system (to orbital forcing) implies a strong amplification of this forcing.” • IPCC 2007 My second point: The problem of extreme global sea level rise • “Because understanding of some important effects driving sea level rise is too limited, this report does not assess the likelihood, nor provide a best estimate or an upper bound for sea level rise.” • (IPCC 2007) More problems with extreme global sea level rise • The long term rise in sea level (beyond 2100) will be made “significantly larger” by the breakdown of the West Antarctic and/or Greenland ice sheets. In Greenland, …this is likely to happen by 2100 under the A1B scenario…This questions both the long-term viability of many coastal settlements and infrastructure…and the current trend of increasing human use of the coastal zone…This issue presents a challenge for long-term coastal spatial planning.”…………..IPCC 2007 Prospective global sea level rise (meters) an “apples and oranges” comparison Rise Cond. Ice loss? End Date Source 0.3 - 0.6 BAU No 2090-99 IPCC 07 >> 0.6 BAU Yes 2090-99 IPCC 07 Rahmstorf 07 0.5 - 1.4 dh/dT No 2100 Hansen et 07 <5 Nonlin.R. No 2100 Delta C. 08 0.7 - 1.3 N.A. ? 2100 Delta C. 08 2–4 N.A. ? 2300 Pfeffer et 08 0.8 - 2 Glacial Yes 2100 Rohling 08 0.5 – 1.5 Paleo.c. Yes 2100 USCCSP 08 >> 0.6 BAU Yes 2100 One outlook for abrupt climate change (IPCC 2007) • “Abrupt climate changes…are not considered likely to occur in the 21st century…However, the occurrence of such changes becomes increasingly more likely as the perturbation of the climate system progresses.” • (a modeling-limited outlook) An outlook for edges of polar ice sheets (USCCSP 2008) • About recent, rapid changes at the edges of • polar ice sheets: “It is unclear whether this imbalance is a shortterm natural adjustment or a response to recent climate change, but processes causing accelerations are enabled by warming, so these adjustments will very likely (90% probability) become more frequent in a warmer climate.” • (an observation span-limited outlook) My third point. Desired recommendations on extreme sea level for planning purposes • In feasibility studies for coastal projects, “consider the high probability of accelerated sea level rise” and “strategies that would be appropriate for the entire range of uncertainty.” • NRC 1987. Responding to Changes in Sea Level, Engineering Implications My wish list for estimates by others of extreme sea level rise • Consider new (or adjusted) “story lines” of a future world with greenhouse gases and changed regional and global temperatures • Obtain best professional judgment of scientists on conditions likely to trigger polar ice sheet collapse • Provide critical review of published estimates of rates and amounts of sea level rise A Faith Statement Amid Chaos and Climate Change • “It is important not to be fatalistic about the threats posed by abrupt climate change.” • ………NRC 2002 My observation and hope • The short time spans of observations and the shortcomings of models presently contribute to a comfortable blanket of uncertainty that shields us from a clear view of future climate. • Perhaps chaos will bring a new, yet liveable, stage of stability to global and regional climate. • [email protected] Your Comments on some places to look for chaos in climate changes? • • • • • 1. hydrologic cycle 2. flow of the Gulf Stream 3. release of trapped methane 4. ecosystem changes 5. human systems changes • [email protected] Your comments on more places to look for chaos in climate changes? • • • • • • 6. the global carbon cycle 7. clouds 8. aerosols 9. ocean wind patterns and currents 10. rapid polar glacier melting 11. changes in albedo • [email protected]