Abstract
We consider alternative history scenarios in which explicit climate mitigation begins before the present day, estimating the total costs to date of delayed action. Considering a 2(1.5) degree Celsius stabilization target, peak costs are greater and reached sooner with a later start to mitigation, reaching 15(17)% of global GDP in 2085(2070) for a 1990 start and 18(35)% in 2080(2035) for a 2020 start. Further mitigation delay costs a best estimate of an additional 0.5(5) trillion dollars per year. Additional simulations show how optimal mitigation pathways evolve without imposing a warming limit, finding that median abatement levels and costs are not strongly dependent on start date. However, whereas 18(5) percent of optimal solutions starting in 1980 meet the 2(or 1.5) degree target, 5(or 0)% of 2020 simulations meet the goals. Discounted damages due to delayed mitigation action rise by 0.6 trillion US dollars per year in 2020.
Highlights
We consider alternative history scenarios in which explicit climate mitigation begins before the present day, estimating the total costs to date of delayed action
A subset of integrated assessment models (IAMs), so-called benefit-cost IAMs3, are the primary type of research tool used to evaluate multiple costs and benefits of climate change policies[4]. Their representation of economic damages from climate change impacts, is usually defined as aggregate relationships between global average warming levels and damages whose parameters are defined by meta-analysis[5]. These “damage functions” are uncertain: there is physical model disagreement on how some key future economic damages such as extreme rainfall will scale with temperature[6], and Earth System Models generally lack the complexity to fully resolve the dynamic ice-sheet processes necessary to capture the range of possible sea level rise[7]
From a socio-economic perspective, there is wide uncertainty in how changes in the climate system translate to impacts on the economy, and how that translation will depend on the changing vulnerability of society over time[8,9]
Summary
We consider alternative history scenarios in which explicit climate mitigation begins before the present day, estimating the total costs to date of delayed action. A subset of integrated assessment models (IAMs), so-called benefit-cost IAMs3, are the primary type of research tool used to evaluate multiple costs and benefits of climate change policies[4] Their representation of economic damages from climate change impacts, is usually defined as aggregate relationships between global average warming levels and damages whose parameters are defined by meta-analysis[5]. IAMs need to represent mitigation of greenhouse gases in the context of a set of model variables This implementation varies by IAM, subject to assumed technological[23] and economic pathways[24] and baseline characteristics25 - which can result in a wide range of possible costs for achieving a given abatement level. By sampling the marginal abatement cost function parameters in DICE, a range of costs can be simulated consistent with the uncertainties in the IAM literature (see Fig. 1(a))
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