A sequential-decision strategy for abating climate change
James K. Hammitt*, Robert J. Lempert* & Michael E. Schlesinger†
*RAND, 1700 Main Street, Santa Monica, California 90407-2138, USA
†Department of Atmospheric
Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory Avenue,
Urbana, Illinois 61801, USA
CURRENT debate on policies for limiting climate change due to greenhouse-gas
emissions focuses on whether to take action now or later, and on how stringent
any emissions reductions should be in the near and long term. Any reductions
policies implemented now will need to be revised later as scientific
understanding of climate change improves. Here we consider the effects of a
sequential-decision strategy (Fig. 1) consisting of a near-term period
(1992–2002) during which either moderate emissions reductions (achieved by
energy conservation only) or aggressive reductions (energy conservation coupled
with switching to other fuel sources) are begun, and a subsequent long-term
period during which a least-cost abatement policy is followed to limit global
mean temperature change to an optimal target ΔT
*. For each policy we
calculate the global mean surface temperature change ΔT(t) using a simple
climate/ocean model for climate sensitivities ΔT
2x. (the response to doubled
CO2, concentrations) of 4.5,2.5,1.5 and 0.5 °C. The policy beginning with
moderate reductions is less expensive than that with aggressive reductions if
*>2.9, 2.1, 1.5 and 0.9 °C respectively; otherwise, the
aggressive-reductions policy is cheaper. We suggest that this approach should
assist in choosing realistic targets and in determining how best to implement
emissions reductions in the short and long term.
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