Geoscience Reference
In-Depth Information
these details for any of the major tipping elements involved in global
warming.
Even if we understand the dynamics of earth systems, a further dif-
fi culty is to determine the gravity of the consequences. This can be
demonstrated by continuing the analysis of the GIS and sea-level rise.
We know the elevation of most places on earth and have reasonable
estimates of how seriously different locations would be threatened by
sea-level rise today.
But knowing the quantitative sea-level rise does not help us very
much in understanding its economic and social impacts. It is diffi cult to
estimate the consequences if the oceans rise two or three centuries from
now because we don't know where people will be living, or whether
they will have taken adaptive measures to protect their houses from sea-
level rise if they know it is coming, or even what kind of houses people
will be living in. If you think about the differences between modern
houses and those of the eighteenth century, you can grasp how diffi cult
it is to estimate the impact of future changes like sea-level rise on hu-
man societies two or three centuries from now. (I return to an assess-
ment of sea-level rise in Part III.)
Other tipping points are even more diffi cult to assess. Scientists can
estimate the scope and timing of melting of Arctic sea ice in the sum-
mer. But the impact of this melting on commerce, wildlife, and ecosys-
tems is very diffi cult to measure. What will it mean for Russia or Canada
if their northern ports are open to shipping six months of the year?
Equally perplexing issues involve the impacts of large-scale changes in
the Amazon rain forest or the Sahara region. We might suppose that
any change is unwelcome because people have adapted to the world as
it is today. But that does not help us understand how serious it would be
if the Sahara turned green or if the Amazon rain forest were trans-
formed into savannah.
The research on tipping points is in its infancy. Scientists have al-
ready found new potential tipping elements since the fi rst draft of this
book was written. We can take steps to reduce the chances of crossing
these boundaries, which are covered later in this topic. But the main
point to emphasize is that potentially dangerous discontinuities can oc-
