Geoscience Reference
In-Depth Information
key factors in selecting targets, a point which is reinforced in the next
section.
The next scenario, which is not shown graphically, is full participa-
tion and discounting. This case would be the ideal for “discount-prone
optimists,” who believe that we should discount future benefi ts but
are optimistic about achieving near-universal participation of differ-
ent countries. The optimal temperature target in this last case is 2.8°C.
This is about
1
⁄
2
°C higher than the no-discounting case shown in Figure
29, but lower than the zero-discounting case with low participation.
This again shows how important participation is in reaching the ideal of
limited climate change and low abatement costs.
What should we conclude from these analyses of costs and benefi ts?
These diagrams are simplifi ed but not overly so. They capture the major
forces at work:
• The higher damages with higher temperatures
• The higher costs of abatement with lower temperature targets
• The increase in costs with low participation and ineffi cient abate-
ment
• The lower damage costs with discounting
The full integrated assessment models contain more detail and examine
the dynamics of moving from today's starting point to different targets.
But the basic points of integrated assessment analysis are retained in
these stylized examples.
COST-BENEFIT ANALYSIS WITH TIPPING POINTS
Most economic analyses of climate change do not include estimates
of the impacts of major earth system tipping points and discontinuities.
Look at the damage curves in Figures 29 to 31. Damages rise gradually
as global temperatures increase on the horizontal scale. This shape de-
rives from the economic damage studies reviewed in Chapter 17 and is
the standard approach used in economic integrated assessment models.
They generally exclude the tipping points because we have no reliable
