The 21st Century climate challenge

parts per million (ppm) of carbon dioxideequivalent (CO 2e) exceeding the natural rangeof the last 650,000 years. In the course of the21 st Century, average global temperatures couldincrease by more than 5°C.To put that figure in context, it is equivalentto the change in temperature since thelast ice age—an era in which much of Europeand North America was under more than onekilometre of ice. The threshold for dangerousclimate change is an increase of around 2°C.This threshold broadly defines the point atwhich rapid reversals in human developmentand a drift towards irreversible ecological damagewould become very difficult to avoid.Behind the numbers and the measurementis a simple overwhelming fact. We are recklesslymismanaging our ecological interdependence.In effect, our generation is running up anunsustainable ecological debt that future generationswill inherit. We are drawing down thestock of environmental capital of our children.Dangerous climate change will represent theadjustment to an unsustainable level of greenhousegas emissions.Future generations are not the only constituencythat will have to cope with a problemthey did not create. The world’s poor will sufferthe earliest and most damaging impacts. Richnations and their citizens account for the overwhelmingbulk of the greenhouse gases lockedin the Earth’s atmosphere. But, poor countriesand their citizens will pay the highest price forclimate change.The inverse relationship between responsibilityfor climate change and vulnerability to itsimpacts is sometimes forgotten. Public debatein rich nations increasingly highlights the threatposed by rising greenhouse gas emissions fromdeveloping countries. That threat is real. Butit should not obscure the underlying problem.Mahatma Gandhi once reflected on how manyplanets might be needed if India were to followBritain’s pattern of industrialization. We areunable to answer that question. However, weestimate in this Report that if all of the world’speople generated greenhouse gases at the samerate as some developed countries, we wouldneed nine planets.While the world’s poor walk the Earthwith a light carbon footprint they are bearingthe brunt of unsustainable managementof our ecological interdependence. In richcountries, coping with climate change to datehas largely been a matter of adjusting thermostats,dealing with longer, hotter summers,and observing seasonal shifts. Cities likeLondon and Los Angeles may face floodingrisks as sea levels rise, but their inhabitantsare protected by elaborate flood defencesystems. By contrast, when global warmingchanges weather patterns in the Horn ofAfrica, it means that crops fail and people gohungry, or that women and young girls spendmore hours collecting water. And, whateverthe future risks facing cities in the rich world,today the real climate change vulnerabilitieslinked to storms and floods are to be foundin rural communities in the great river deltasof the Ganges, the Mekong and the Nile, andin sprawling urban slums across the developingworld.The emerging risks and vulnerabilitiesassociated with climate change are the outcomesof physical processes. But they are alsoa consequence of human actions and choices.This is another aspect of ecological interdependencethat is sometimes forgotten. Whenpeople in an American city turn on the airconditioningor people in Europe drive theircars, their actions have consequences. Thoseconsequences link them to rural communitiesin Bangladesh, farmers in Ethiopia and slumdwellers in Haiti. With these human connectionscome moral responsibilities, including aresponsibility to reflect upon—and change—energy policies that inflict harm on other peopleor future generations.The case for actionIf the world acts now it will be possible—justpossible—to keep 21 st Century global temperatureincreases within a 2°C threshold abovepreindustrial levels. Achieving this future willrequire a high level of leadership and unparalleledinternational cooperation. Yet climate change isa threat that comes with an opportunity. Aboveall, it provides an opportunity for the world toWe are recklesslymismanaging our ecologicalinterdependence. Ourgeneration is runningup an unsustainableecological debt that futuregenerations will inheritHUMAN DEVELOPMENT REPORT 2007/2008 3