Climate change futures: health, ecological and economic dimensions

CLIMATE CHANGE CANOCCUR ABRUPTLYPerhaps the most daunting factor complicating the taskof estimating the future health and economic impactsof climate change is that most climate futures and insuranceindustry projections drastically underestimate therate at which climate might change.on linear extrapolations of past trends and current trajectories,though the insurance industry has long considered“catastrophe theory” to project the impacts ofsudden, extreme losses. However, these models do notpredict the probabilities of such events. For climate,increasing rates of change and greater volatility aresigns of instability and suggest greater propensity forsudden change (Epstein and McCarthy 2004).26 | THE CLIMATE CONTEXT TODAYMost envisioned climate futures of international assessmentsto date are based on gradual projections ofincreasing temperatures. Some include temperaturevariability, and others have begun to examine variancein weather patterns. But most do not reflect thehigh degree of variance in weather that is alreadyoccurring and few address the potential consequencesof sudden change in impacts or abrupt shifts in climateitself.The notion that climate might change suddenly, or shiftfrom state to state, rather than change gradually —what Richard Alley calls the “switch” rather than the“dial” model for climate change — seemed like a radicalnotion when it first began to take hold in the early1990s. In nature, however, sudden shifts are the rule,not the exception.Steven J. Gould’s conception of evolution as “punctuatedequilibrium” depicts long periods of relative stabilitywith gradual change, punctuated by periods of massextinctions. These “interruptions” are then followed bythe explosion of new species with new solutions tonew environmental problems that fit together into newcommunities of organisms.On a more immediate time scale, non-linear changesare part of our daily experience. When temperatureschange, liquid water can suddenly transform into ahard, latticed structure as it freezes or vaporizes, whenit boils. Damage functions are also non-linear. Forexample, hailstones tend to bounce off of windshieldsuntil they reach a critical weight and break them.Though abrupt climate change is a ubiquitous phenomenonand is observed throughout ice, pollen, fossiland geological records (NAS 2002), the bias towardgradual, incremental change may reflect the constraintsof climate models that represent our best understandingof how dynamic systems behave. Models have a difficulttime incorporating step-wise changes to newstates. Most industries naturally base their projectionsEven more challenging is the observation that changesin state can be triggered by small forces that approach(often unforeseen) thresholds or “tipping points” — andsurpass them. Disease outbreaks can slowly grow inimpact, for example, then suddenly become epidemics.For the climate, the transitions between glacial andinterglacial warm periods can involve changes from5-10°C (9-18°F) in the span of a decade or less(Steffan et al. 2004b). Sudden shifts are sometimesrestricted in geographic scope. At other times there areglobal transformations (Severinghaus et al. 1998;NAS 2002; Alley et al. 2003). Many such “highimpact” events that were considered “low probability”just several years ago now seem to some increasinglylikely (Epstein and McCarthy 2004) or inevitable(NAS 2002).TIPPING POINTSPOSSIBLE “CLIMATE SHOCKS” WITH LIMITEDGEOGRAPHIC IMPACTS• Small sections of Greenland, the West Antarctic IceSheet (WAIS) or the Antarctic Peninsula could slipinto the ocean, raising sea levels several inches tofeet over years to several decades.o Meltwater is seeping down through crevasses inGreenland, lubricating the base of large glaciers(Krabill et al. 1999; ACIA 2005).o “Rivers of ice” in the WAIS are acceleratingtoward the Southern Ocean (Shepherd et al.2001; Payne et al. 2004; Thomas et al. 2004).o Recent loss of floating ice shelves along theAntarctic Peninsula removes back pressure from theland-based ice sheets (Rignot and Thomas 2002).• Alpine glacial melting could accelerate, inundatingcommunities below and diminishing water suppliesfor nations dependent on this source for freshwater.