Trapped between two tails: trading off scientific uncertainties via climate targets

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Trapped between two tails: trading off scientific uncertainties via climate targets
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Climate change policies must trade off uncertainties about future warming, about the social and ecological impacts of warming, and about the cost of reducing greenhouse gas emissions. We show that laxer carbon targets produce broader distributions for climate damages, skewed towards severe outcomes. However, if potential low-carbon technologies fill overlapping niches, then more stringent carbon targets produce broader distributions for the cost of reducing emissions, skewed towards high-cost outcomes. We use the technology-rich GCAM integrated assessment model to assess the robustness of 450 and 500 ppm carbon targets to each uncertain factor. The 500 ppm target provides net benefits across a broad range of futures. The 450 ppm target provides net benefits only when impacts are greater than conventionally assumed, when multiple technological breakthroughs lower the cost of abatement, or when evaluated with a low discount rate. Policy evaluations are more sensitive to uncertainty about abatement technology and impacts than to uncertainty about warming.

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clock pulses must fit of several types of uncertainties there's uncertainty but the war pre-speech emission path certainty that damages priest but in a given amount of warming and uncertainty about technologies of the available to reduce emissions in the future and our paper trapped between 2 tails trading of scientific uncertainties via climate targets the monarchy and I analyze these uncertainties trying to figure out which ones are most crucial to economic evaluations of climate policy in the 1st
part of the paper we show how uncertainty about warming skews just from climate change was undesirable outcomes however uncertainty about the future low-carbon technology makes a cost-reducing mission skew toward more expensive outcomes with technology so similar niches at the partially substitute for each other it breakthrough any 1 technology is most valuable when other technologies have not also had breakthroughs the 2nd part of the paper develops a
framework for quantitatively comparing homeport uncertainties are to economic evaluation the climate targets we couple technology which global change assessment model the damage functions common a more stylized policy optimizing integrate assessment models in order to quantitatively compare these users novel combination to evaluate the cost the benefits of hitting 1 climate targets instead of 1 a slightly weaker in particular
display graph compares 450 ppm target of 500 part civilian targets includes 384 technology features 5 times to be scenarios and for damage functions virtual 7 thousand 680 results this graph visually organizes thousands of results we translate each result the what we call the break-even lost how bad most 2 comma decimal 5 degrees celsius a morning the in order to justify of 450 ppm target under a given combination technology damaging climate assumptions the shady areas that pick the range of loss assessments in the economics literature breaking losses about the year there not economical and the most studies estimates that losses in the dark a shaded area are economical under many studies estimates 1st we see that the wall technology inserting each box and whiskers this uncertainty creates high variance the cost to attain the 450 parts 2 million target in line with the simple theoretical analysis those cost you toward expensive outcomes because technologies partially substitute for each other in G can 2nd compare across columns of than a grouping gives effect of changing climate sensitivity choosing higher values makes emissions have generate more warming in that case the more stringent policies more valuable this is why we see the boxes steps steadily down toward the low break-even losses however better information appliances to be does not affect policy evaluation as strong as better information about technology for instance which the 75th the 50th percentile technology outcome have a similar effect is increasing estimator crimes by full degrees Celsius which would be a rather large change role to the past centuries history of 3rd by comparing groups of
columns we see the importance assumptions about how we extrapolate damages from moderate wells the warming to high of warning the choice of damage functions a strong effect for instance switching for the quadratic cubic function making damages increase faster with warming has a similar effect is raising estimated crimes tivity from 3 to 4 degrees Celsius switching from quadratic to the
additive function has a strong effect is reading as many consistently from 3 to 4 degrees Celsius while also switch the quadratic cubic damage function crucially these damage functions are essentially pure assumptions this pure assumptions matter strongly for policy evaluation much
scientific research gone testimony many times tivity we find a policy evaluation so well so robust to the meaning uncertainty however they're not robust uncertainty but damages damages or technology what technological change is inherently uncertain there's high value to better understand that process and implementing more sophisticated representations in modern just a future warmer world also inherently uncertain there's high value to analyze the pathways which future climate change matters into better integrating scientific and economic knowledge in order to ground damage estimates forecast of warming technology in damages cannot avoid going far out a sample beginning current knowledge acquired the I results suggest prioritizing efforts to better define damage in technology possibilities