Geoscience Reference
In-Depth Information
The major qualifi cation centers on the diffi culty of assessing the
impacts of tipping points—the potentially discontinuous, abrupt, and
catastrophic climate changes and consequences. The economic impacts
of the potential singularities are diffi cult to estimate for the same rea-
sons as those of species and ecosystem losses. They are hard to forecast;
the physical impacts are unknown; and the consequences generally
lie far outside the marketplace. The challenges are compounded here
because the effects may threaten the biological and physical founda-
tions of human and natural societies. In this respect, they are similar
to existential debates about national security, where it is diffi cult to
measure the costs and benefi ts of different strategies. At this stage, the
physical sciences still have far to go in understanding the threats from
these large-scale tipping points. Once those are better known, we can
attempt to understand the dangers they pose to social and natural sys-
tems as well as the steps required to prevent these geophysical bank
runs.
What should we conclude at the end of this review of the impacts of
future climate change? The fi rst point to emphasize is the diffi culty of
estimating impacts. They combine the uncertainties of emissions pro-
jections and climate models. Even if we overlook the uncertainties about
future climate change, the reactions of human and other living systems
to these changes are very poorly understood. In part, reactions of social
systems are hard to forecast because they are so complex. In addition,
humans increasingly manage their own environment, so that a small
investment in adaptation may offset the impact of climate change on
human societies. Moreover, climate changes are almost certain to occur
in the context of technologies and economic structures that will differ
vastly from those of today.
However, we must look through the fuzzy telescope as best we can.
A second conclusion involves the estimated economic impacts of cli-
mate change from sectors that we can reliably measure, particularly for
high-income countries of today or the future. The estimates here are
that the economic impacts from climate change will be small relative
to the likely overall changes in economic activity over the next half
