The 21st Century climate challenge

2Climate shocks: risk and vulnerability in an unequal worldCoral reefs are not justhavens of exceptionalbiodiversity, but also asource of livelihoods,nutrition and economicgrowth for over 60 countriesOther ecosystems provide an equally sensitivethough less immediately visible barometer. Coralreefs are an example. During the 21 st Century,warming oceans and rising acidification coulddestroy much of the world’s coral, with devastatingsocial, ecological and economic consequences.Warming seas have contributed to thedestruction of coral reefs on an extensivescale, with half of all systems in decline. 102Even fairly short periods of abnormally hightemperature—as little as 1°C higher than thelong term average—can cause corals to expel thealgae that supply most of their food, resulting in‘bleaching’ and sudden death of the reef. 103The world’s coral reef systems alreadybear scars from climate change. Around halfthese systems have already been affected bybleaching. The 50,000 km 2 of coral reef inIndonesia, 18 percent of the world’s total,is deteriorating rapidly. One survey in BaliBarat National Park in 2000 found that themajority of the reef had been degraded, mostof it by bleaching. 104 Aerial views of the GreatBarrier Reef in Australia also capture theextent of bleaching.There could be far worse to come. Withaverage temperature increases above 2ºC,annual bleaching would be a regular event. Themajor bleaching events that accompanied the1998 El Niño, when 16 percent of the world’scoral was destroyed in 9 months, would becomethe rule, rather than the exception. Localizedbleaching episodes are becoming more frequentin many regions, providing a worrying pointerfor the future. For example, in 2005, the easternCaribbean suffered one of the worst bleachingepisodes on record. 105Bleaching is just one of the threats posedby climate change. Many marine organisms,including coral, make their shells and skeletonsout of calcium carbonate. The upper ocean issuper-saturated with these minerals. However,the increases in ocean acidity caused by the 10billion tonnes of CO 2being absorbed by theoceans each year attacks carbonate, removingone of the essential building blocks neededby coral. 106Marine scientists have pointed to a worryingparallel. Ocean systems respond slowly andover very long time horizons to changes in theatmospheric environment. Business-as-usualclimate change in the 21 st Century couldmake the oceans more acidic over the next fewcenturies than they have been at any time for300 million years, with one exception: a singlecatastrophic episode that occurred 55 millionyears ago. That episode was the result of therapid ocean acidification caused by the releaseof 4,500 gigatonnes of carbon. 107 It took over100,000 years for the oceans to return to theirprevious acidity levels. Meanwhile, geologicalrecords show a mass extinction of sea creatures.As one of the world’s leading oceanographersputs it: “Nearly every marine organism thatmade a shell or a skeleton out of calciumcarbonate disappeared from the geologic record… if CO 2emissions are unabated, we may makethe oceans more corrosive to carbonate mineralsthan at any time since the extinction of thedinosaurs. I personally believe that this willcause the extinction of corals.” 108The collapse of coral systems would representa catastrophic event for human development inmany countries. Coral reefs are not just havensof exceptional biodiversity, but also a source oflivelihoods, nutrition and economic growthfor over 60 countries. Most of the 30 millionsmall-scale fishers in the developing world aredependent in some form on coral reefs for maintainingfeeding and breeding grounds. Morethan half of the protein and essential nutrientsin the diets of 400 million poor people living intropical coastal areas is supplied by fish.Coral reefs are a vital part of the marineecosystems that sustain fish stocks, thoughwarming oceans pose wider threats. In Namibia,anomalously warm water currents in 1995—theBenguela Niño current—resulted in fish stocksmoving 4–5° of latitude south—an outcomethat destroyed a small-scale fisheries industryfor pilchards. 109Beyond their value in the lives and nutritionof the poor, corals have a wider economic value.They generate income, exports and, in regionssuch as the Indian Ocean and the Caribbean,support tourism. Recognition of the importantrole of coral in economic, ecological and sociallife has prompted many governments and aid104 HUMAN DEVELOPMENT REPORT 2007/2008