The 21st Century climate challenge

justification for inaction. They are an invitationto assess the nature of identified risks and todevelop strategies for risk mitigation. As a groupof eminent United States military leaders hasargued, no commander in the field would lookat risks comparable to those posed by climatechange and decide not to act because of uncertainty:“We cannot wait for certainty. Failingto act because a warning is not precise enoughis not acceptable.” 50The nature of the risks associated withclimate change uncertainties reinforces thatassessment on three counts. First, these arerisks that threaten the whole of future generationsof humanity with catastrophic outcomes.The sea level rises that would accompany thecollapse of the ice sheets on Greenland andthe West Antarctic would overwhelm theflood defences of even the richest countries,submerging large areas of Florida and muchof the Netherlands, as well as inundating theGanges Delta, Lagos and Shanghai. Second,the outcomes associated with the risks areirreversible: the West Antarctic ice sheetcannot be restored by future generations.Third, uncertainty cuts both ways: there is asmuch chance of outcomes being more malignas there is of them being more benign.In a one-country world inhabited by citizenswho shared a concern for the well-being offuture generations, climate change mitigationwould be an urgent priority. It would be viewedas an insurance policy against catastrophic riskand as an imperative rooted in considerationsof cross-generational equity. Uncertainty inthis one-country world would be viewed not asgrounds for inaction but as evidence of the casefor acting with resolve to reduce the risks.In a world of many countries at vastlydifferent levels of development there is acomplementary case for urgent action. That caseis first of all rooted in considerations of socialjustice, human rights and ethical concern forthe world’s poorest and most vulnerable people.Millions of these people are already dealingwith the early impacts of climate change. Theseimpacts are already slowing human progressand all plausible scenarios point to more of thesame, and worse. Because mitigation will have alimited influence on climate change for severaldecades, investment in adaptation should beseen as part of the insurance policy for theworld’s poor.Both mitigation and adaptation should beseen as human security imperatives in a broadersense. Dangerous climate change, and theecological damage that will follow in its wake,threatens to cause massive human displacementand the collapse of livelihoods on a vast scale.The ripple effects would extend far beyond thelocalities of those most immediately affected.Associated outcomes will extend from themovement of displaced people across nationalborders to the potential collapse of fragile states.In an interdependent world, no country wouldbe immune to the consequences. Of course,many rich countries might seek to protect theircitizens against climate insecurity throughinvestment in flood defences and other actions.However, the anger and resentment that wouldbe felt by those most immediately affectedwould create wider insecurities.In a one-country worldinhabited by citizens whoshared a concern forthe well-being of futuregenerations, climatechange mitigation wouldbe an urgent priority1The 21 st Century climate challenge1.3 From global to local—measuring carbon footprintsin an unequal worldFor global carbon accounting purposesthe world is a single country. The Earth’satmosphere is a common resource withoutborders. Emissions of greenhouse gases mixfreely in the atmosphere over time and space.It makes no difference for climate changewhether the marginal tonne of CO 2comesfrom a coal-fired power plant, from a car,or from a loss of carbon sinks in tropicalrainforests. Similarly, when greenhouse gasesenter the Earth’s atmosphere they are notsegmented by country of origin: a tonne ofHUMAN DEVELOPMENT REPORT 2007/2008 39