Geoscience Reference
In-Depth Information
assessment model, they are consistent with the projections of more
detailed modeling studies.
10
IMPACTS
What are the potential impacts of SLR over the coming century and
beyond? We know that the oceans have risen and fallen over geological
history. When humans fi rst came to America, the oceans were at least
90 meters (300 feet) lower than today. (Ice age discovery of the New
World is an example of how environmental changes can lead to innova-
tive behavior.) In the last warm period, when global temperatures were
1-2°C warmer than today, the oceans were about 3 meters (10 feet)
higher. In still earlier periods, sea level was perhaps 180 meters (600 feet)
higher in the age of the dinosaurs, when glaciers were largely absent.
However, the pace of SLR over the coming century and beyond is
unprecedented for the period of human civilizations. Reconstructions
suggest that the level of the ocean has changed by less than 1 meter (3
feet) over the last 4,000 years. Ecologists are particularly concerned about
the impact of the rising ocean as it interacts with coastal ecosystems.
Here I concentrate on the social dimensions.
I discussed earlier the problem of the fuzzy telescope—that project-
ing impacts becomes increasingly diffi cult the further we go into the
future. This can be seen dramatically for SLR. In many places, cities are
built, grow, and decline over the course of a century. So while we can
easily measure the impact of SLR on current settlements, the impact on
those in a century or more looks fuzzy indeed.
We can, however, examine the extent of current vulnerability to
SLR by looking at where people live and work today. About 4 percent of
the world's population and output are in regions at elevations at or below
10 meters (33 feet). I call this the “red zone” at risk of SLR, although it
probably exaggerates the extent of endangered people or output. Because
people and economic activity tend to cluster near coastlines, there are
more people and output than land in the red zone.
The vulnerability of regions is determined not just by their eleva-
tion, however. In areas subject to hurricanes or intense storms, fl ooding
can pose major risks even for higher locations. But, for the most part,
