The 21st Century climate challenge

1The 21 st Century climate challengeFigure 1.12Emissions per capita for stabilization at 450 ppm CO 2e (t CO 2per capita)181614121086420did, it is unlikely that they would embrace anagreement that allowed ‘free riding’.Participation of the developing world inquantitative reductions is equally vital. In somerespects, our ‘two-country’ model oversimplifiesthe issues to be addressed in negotiations. Thedeveloping world is not homogenous: the UnitedRepublic of Tanzania is not in the same positionas China, for example. Moreover, what mattersis the overall volume of emission reductions.From a global carbon budget perspective,deep reductions in sub-Saharan Africa carrynegligible weight relative to reductions in majoremitting countries.However, with developing countriesaccounting for nearly half of worldwide emissions,their participation in any internationalagreement is increasingly important. At thesame time, even high growth developingcountries have pressing human developmentneeds that must be taken into account. So toomust the very large ‘carbon debt’ that the richcountries owe the world. Repayment of thatdebt and recognition of human developmentimperatives demand that rich countries cutemissions more deeply and support low-carbontransitions in the developing world.We acknowledge that many other emissions’pathways are possible. One school of thought2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100Source: Meinshausen 2007.Contracting and converging to a sustainable futureDeveloped and transition countriesDeveloping countriesNote: IPCC scenarios describe plausible future patterns of population growth, economic growth, technologicalchange and associated CO 2emissions. The A1 scenarios assume rapid economic and population growthcombined with reliance on fossil fuels (A1FI), non-fossil energy (A1T) or a combination (A1B). The A2 scenarioassumes lower economic growth, less globalization and continued high population growth. The B1 and B2scenarios contain some mitigation of emissions, through increased resource efficiency and technologyimprovement (B1) and through more localized solutions (B2).Worldargues that every person in the world ought to enjoyan equivalent right to emit greenhouse gases, withcountries that exceed their quota compensatingthose that underutilize their entitlement. Althoughproposals in this framework are often couched interms of rights and equity, it is not clear that theyhave a rights-based foundation: the presumed‘right to emit’ is clearly something different thanthe right to vote, the right to receive an educationor the right to enjoy basic civil liberties. 62 At apractical level, attempts to negotiate a ‘pollutionrights’ approach is unlikely to gain broad support.Our pathway is rooted in a commitment to achievea practical goal: namely, the avoidance of dangerousclimate change. The route taken requires a processof overall contraction in greenhouse gas flows andconvergence in per capita emissions (figure 1.12).Urgent action and delayedresponse—the case for adaptationDeep and early mitigation does not offer a shortcutfor avoiding dangerous climate change. Oursustainable emissions pathway demonstrates theimportance of the time lag between mitigationactions and outcomes. Figure 1.13 captures thelag. It compares the degree of warming abovepreindustrial levels associated with the IPCC’snon-mitigation scenarios, with the anticipatedwarming if the world stabilizes greenhouse gasstocks at 450 ppm CO 2e. Temperature divergencebegins between 2030 and 2040, becoming moreemphatically marked after 2050, by which timeall but one of the IPCC scenarios breach the 2°Cdangerous climate change threshold.The timing of the temperature divergencedraws attention to two important public policyissues. First, even the stringent mitigationimplied by our sustainable emissions pathwaywill not make a difference to world temperaturetrends until after 2030. Until then, the worldin general and the world’s poor in particularwill have to live with the consequences of pastemissions. Dealing with these consequenceswhile maintaining progress towards the MDGsand building on that progress after 2015 is amatter not for mitigation but for adaptation.Second, the real benefits of mitigation willbuild cumulatively across the second half of the21 st Century and beyond.50 HUMAN DEVELOPMENT REPORT 2007/2008