A Critical Conversation on Climate Change ... - Green Choices

16 development dialogue september 2006 – carbon tradingWorlds inside ComputersGeneral Circulation Models (GCMs) areminiature, closed worlds created insidecomputers. Consisting of tens of thousandsof lines of computer code, each GCM calculateshow climate might change in aparticular imaginary world over decadesor centuries, given certain initial assumptions.These models – there are dozens of them inuse in various places – are based on solid principlesof physics. Taken together, they give afeel for how climate might change in the realworld. But their usefulness can’t be checkedby experiment in the ordinary sense, andthere are things they cannot tell us.First, GCMs are highly simplified whencompared with the real climate system.Second, all of them are likely to have leftout certain mechanisms influencing climatethat are not yet known. 50 This difficultyis made more serious by the fact thatmany models share a common heritage.‘Typically, one modelling group “borrows”another group’s model and modifiesit, meaning that the “new” models mayretain problematic elements of those fromwhich they were created’, replicating systematicerrors. 51Third, the global data that models use havecertain limitations – limitations exacerbatedby the fact that many of the data are generatedby the models themselves, to fill inblanks needed to run global simulations. 52Fourth, models are characterised by variouskinds of uncertainty. For instance, theyare extremely sensitive to initial assumptions,meaning that different runs will yieldhugely different results. No particular runof a model can be expected to reflect thereal climate system, in which, also, smallchanges at one location and time can leadto large differences at other locations andtimes. 53 Climate modelling generates whatone analyst calls ‘mutated’ facts full of theories,uncertainties and ambiguities – factsthat have to be grasped ‘as much with yourimagination as with your calculator’. 54 Thatdoes not make them any less worthy of attention.So if conventional types of economic management are out the window, whatdo we do?A different kind of precaution is needed, one matched to the particularnature of the climate problem.This kind of precaution would acknowledge and attempt to removeignorance and uncertainty. It would try to maximise flexibility, resilienceand possibilities for future learning. And in the meantimeit would avoid irreversible courses of action that are potentially59 60civilisation-threatening.Unavoidably, that means taking better care of the world’s native biota,which constitute a large and volatile storehouse of carbon. But aboveall, it means slowing and halting fossil fuel extraction pending moreresearch into gaps and blind spots.