The 21st Century climate challenge

Figure 1.13Stringent mitigation does notdeliver early resultsSurface warming projections (°C)43210Dangerous climate changeUncertainty range2000 2025 2050 2075 2100Relative to preindustrial levelsSustainable emissions pathway (for illustrative purposes only)IPCC scenario A1BIPCC scenario A2IPCC scenario B1Note: IPCC scenarios describe plausible future patterns ofpopulation growth, economic growth, technological changeand associated CO 2emissions. The A1 scenarios assume rapideconomic and population growth combined with reliance on fossilfuels (A1FI), non-fossil energy (A1T) or a combination (A1B).The A2 scenario assumes lower economic growth, lessglobalization and continued high population growth. The B1 andB2 scenarios contain some mitigation of emissions, throughincreased resource efficiency and technology improvement (B1)and through more localized solutions (B2).Source: IPCC 2007a and Meinshausen 2007.One important implication is that the motivationfor urgent mitigation has to be informedby a concern for future generations. The world’spoor will face the most immediate adverseimpacts of temperature divergence. By the endof the 21 st Century, with some of the IPCCscenarios pointing to temperature increases of4–6°C (and rising), humanity as a whole willbe facing potentially catastrophic threats.The cost of a low-carbontransition—is mitigation affordable?Setting carbon budgets is an exercise that hasimplications for financial budgets. While therehave been many studies looking at the cost ofachieving specific mitigation goals, our 2°Cthreshold is a far more stringent target thanthose assessed in most of these studies. Whileour sustainable climate pathway may be desirable,is it affordable?We address that question by drawing onan approach that combines quantitative resultsfrom a large number of models in order toinvestigate the costs of achieving specified stabilizationoutcomes. 63 These models incorporatedynamic interactions between technology andinvestment, exploring a range of scenarios forachieving specified mitigation targets. 64 Weuse them to identify global costs for achieving atarget of 450 ppm CO 2e.Emissions of CO 2can be cut in several ways.Increased energy efficiency, reduced demandfor carbon-intensive products, changes in theenergy mix—all have a role to play. Mitigationcosts will vary according to how reductions areachieved and the time frame for achieving them.They arise from financing the developmentand deployment of new technologies and fromthe cost to consumers of switching to loweremissionsgoods and services. In some cases,major reductions can be achieved at low cost:increased energy efficiency is an example.In others initial costs can generate benefits overthe longer term. Deployment of a new generationof efficient, low-emission coal-fired powerstations might fit in this category. Graduallyreducing the flow of greenhouse gases over timeis a lower-cost option than abrupt change.Modelling work carried out for this Reportestimates the costs of stabilization at 450 ppmCO 2e under various scenarios. Expressed interms of headline dollars, the figures are verylarge. However, the costs of action are spreadover many years. In a simple reference scenario,averaging out these costs produces a figureof around 1.6 percent of annual world GDPbetween now and 2030. 65That is not an insignificant investment. Itwould be wrong to underestimate the massiveeffort required to stabilize CO 2e emissions closeto 450 ppm. However, the costs have to be putin perspective. As the Stern Review powerfullyreminded the world’s governments, they haveto be evaluated against the costs of inaction.1The 21 st Century climate challengeHUMAN DEVELOPMENT REPORT 2007/2008 51