Page - 358 - in Loss and Damage from Climate Change - Concepts, Methods and Policy Options

358 A.MarkandyaandM.González-Eguino Fig.14.5 Damage (%GDP) fordifferentdamage functionsandECSparameters warming (<2 °C5).Mostmodellers advise that at higher temperatures the damage functions go beyond their useful limits. Nordhaus, for example, suggests that we have insufficientevidence toextrapolate reliablybeyond3°C(NordhausandSztorc 2013).However, it is also true that there is a significant risk of temperatures rising above3°C in thecourseof this century. Figure 14.5 shows the combined effect of the damagewhen the uncertainty in theECSandin thedamagefunctionchoice isconsidered.Weshow,using theDICE model, the damage (as%of globalGDP) for theNordhaus andWeitzmandamage functionsandforthreevaluesfor theECS-1.5,3and4.5.Thedamagesareestimated foralowandhighemissionpathwayscenario(RCP4.5andRCP6),whichareclose to theones reported inSect.14.3.2.Wecansee that the rangeof thedamages is low before 2050 but then expands substantially at the end of this century. The damage per annumby 2100 in the low emission pathways could be 0.8% in the best case scenario (Nordhaus andECS 1.5) and9.5% in theworst (WeitzmanandECS 4.5).Similarly, thedamage in thehighemissionpathwayscould rangebetween1.2 and25%in themoreextremesituations. Finally, andalthough IAMshavebeenhelpful in illustrating the economicdam- age from climate change under different circumstances (Lenton andCiscar 2012; Ackermanetal.2010), these largeuncertaintiesneedtoberecognised.Althoughthe possibilityofcrossingatippingpointduringthiscentury is far fromclear, itmustbe considered apossibility in anyL&Dmechanism that could bedesigned. Similarly, anyfinancemechanisms implementedwill need tobedesigned in themostflexible mannerandconsidering thisextremesituationsowhennewinformation isavailable it canbe incorporatedquicklyaswewill analyse in the followingsection. 5This is the case for example of the abrupt loss ofArctic summer sea ice or permafrost thawing (González-EguinoandNeumann2016;Gonzalez-Eguinoet al. 2017).