Geoscience Reference
In-Depth Information
not a simple matter. It involves, as we will see in coming chapters, tak-
ing steps to change energy systems. And those involve very large costs.
So there is an inevitable trade-off between the costs of our emissions
reductions and the risks of ecosystem and species losses.
How do economists and ecologists go about measuring this trade-
off? This turns out to be the most diffi cult area of all for estimating the
economic damages from climate change. The natural and social sci-
ences have great diffi culty in making reliable estimates of the value of
preserving ecosystems and species. There are two diffi culties—getting
reliable estimates of the losses, and then valuing the losses.
Start with problem one: the diffi culty in making reliable projections
of species losses over time. I illustrate the diffi culties by examining
an infl uential study on species losses and global warming by Thomas et
al. This study concluded that between 18 and 35 percent of species are
“committed to extinction” given current trends in climate change.
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How did they reach this conclusion? The study began by estimating
the climatic range of existing species (including mammals, birds, and
amphibians) in a particular region. Then the team estimated how the
size of the climatic range would change under a particular scenario. For
example, they examined the impact of a 3°C warming on the Proteaceae
species in South Africa (Proteaceae are a family of beautiful fl owering
plants).
Next they applied a technique known as the species-area relation-
ship. This is an empirical law holding that the number of species in-
creases as the area of the habitat increases. For the regions considered
by the team, the climatic range for most species was estimated to shrink
with global warming, implying that the number of species will also
shrink. For example, under the assumed 3°C increase for South Africa,
the researchers concluded that 38 percent of the Proteaceae species will
become extinct because the climatic range supporting the plants will
decline. Perhaps the most carefully studied area of potential extinctions
is the reef-building corals.
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While these studies are widely cited, the methods have severe limi-
tations. To begin with, most studies consider “vulnerable” species as well
as those that are on the brink of extinction. Additionally, some of the
