Climate change futures: health, ecological and economic dimensions

THE PROBLEM:CLIMATE IS CHANGING, FASTThe proposition that climate change poses a threatbecause of an enhanced greenhouse effect inevitablybegs questions. Without greenhouse gases such asCO 2trapping heat (by absorbing long-wave lengthradiation from the earth’s surface), the planet would beso cold that life as we know it would be impossible.For more than two million years, Earth has alternatedbetween two states: long periods of icy cold interruptedby relatively short respites of warmth. During glacialtimes, the polar ice caps and Alpine glaciersgrow; during the interglacial periods, the North Polarcap shrinks, as do Alpine glaciers.Figure 1.1 Simulated Annual Global Mean SurfaceTemperaturesUp until the 20th century, these cycles were driven bythe variations in the tilts, wobbles and eccentricities ofEarth’s orbit — the Milankovitich cycles, named for theSerbian mathematician who deciphered them. Thetemperature changes from the industrial revolution on,however, can only be explained by combining naturalvariability with anthropogenic influences (Houghton etal. 2001) (see figure 1.1). Recent calculations of theselong-wave cycles project that the current interglacialperiod — the Holocene — was not about to end anytime soon (Berger and Loutre 2002).Much of human evolution took place during this latestglacial period; our ancestors survived the cold periodsand prospered during the warmer interregnums, particularlythe most recent span that encompassed the birthand efflorescence of civilization. So, if the climate iswarming, what’s the problem?16 | THE CLIMATE CONTEXT TODAYThe simulations represented by the band in (a) were done with onlynatural forcings: solar variation and volcanic activity. Those in (b)were done with anthropogenic forcings: greenhouse gases and anestimate of sulphate aerosols. Those encompassed by the band in (c)were done with both natural and anthropogenic forcings included.The best match with observations is obtained in (c) when both naturaland anthropogenic factors are included.These charts formed the basis for the IPCC’s conclusion that humanactivities were contributing to climate change.Image: IPCC 2001Climate change may not be a threat to the survival ofour species, but it is a threat to cultures, civilizationsand economies that adapt to a particular climate at aparticular time. Through history, humans as a specieshave survived climate changes and those groups thatmade it through the adversity of “cold reversals” did soby calling on their capacities to communicate, cooperateand plan ahead (Calvin 2002). But many civilizationshave also perished when they could not adaptfast enough. Societies adapt to their current conditions,taking a gamble that those circumstances will continueor change gradually. Never has this been more truethan in the recent past: The explosion of human numbersand the miracles of modern economic developmenthave all taken place during the extraordinary climatestability that has prevailed since the early 19thcentury. The five-billion-person increase in human populationduring that period occurred against the backdropof a climate that was neither too warm, too cold,too dry, nor too wet. In the past, climate change hasbeen driven by the Milankovitch cycles, volcanic eruptionsand the movement of continents. Now, ironically,thanks in part to the nurturing climate of recent centuries,humanity has become a large enough presenceon the planet to itself affect climate. As the evolutionarybiologist E.O. Wilson put it, “Humanity is the firstspecies to become a geophysical force.”In its Third Assessment Report in 2001 (Houghton etal. 2001), the IPCC came to the same insight. Thereport’s four primary conclusions were: Climate ischanging; humans are contributing to those changes;weather is becoming more extreme; and biologicalsystems are responding to the warming on all continents