HISTORICAL PERSPECTIVES ON CLIMATE POLICY - The Climate Casino - page 198

Academy of Sciences report endorsed a 2°C temperature limit for the
world as well as sharply declining emissions limits for the United States. 1
Similar statements have come from other scientifi c bodies around the
world. World leaders in recent years have also agreed on the approach of
limiting temperature increases.
Our task in this chapter is to look inside the covers of such reports
to examine how these objectives have been derived. It might seem
straightforward to set objectives for climate-change policy. We could,
for example, pick a temperature target to keep the world a safe distance
away from dangerous tipping points. Or we might attempt to prevent the
loss of a signifi cant number of species. Perhaps we could select a target
to prevent the melting of the Greenland Ice Sheet. In fact, none of these
choices provides a simple and unambiguous guide for determining cli-
mate targets.
I will discuss how temperature objectives became so central. This
discussion will show that the policy of a specifi c numerical target rests
on weak scientifi c support. There is no bright line for targets at 1 1 ⁄ 2 °C
or 2°C or 3°C or any specifi c temperature increase. The best target will
depend upon the costs of achieving it. We should aim for a lower tem-
perature target if it is inexpensive, but we might have to live with a
higher target if costs are high or policies are ineffective.
The fi nal conclusion of this chapter is that we cannot sensibly set
climate policy targets without economics. We need to consider both
costs and benefi ts—both where we are going and what it costs to get
there.
INTERNATIONAL AGREEMENTS ON CLIMATE CHANGE
Begin with the fi rst statement on climate-change objectives. The
foundation for international climate-change deliberations is the “United
Nations Framework Convention on Climate Change,” ratifi ed in 1994.
This treaty states that “the ultimate objective . . . is to achieve . . . stabi-
lization of greenhouse-gas concentrations in the atmosphere at a level
that would prevent dangerous anthropogenic [i.e., human] interference
with the climate system.” 2 This lofty goal is too vague to be useful for
policy because there is no defi nition or obvious way to determine what