Geoscience Reference
In-Depth Information
incomes comparable to those of North America today and also as-
sume that large numbers will still be nomads herding cattle across the
desert.
Second, one of the regularities of economic development is that
societies increasingly insulate their populations from all kinds of ad-
verse shocks. We see this in the area of public and private health, agri-
cultural shocks, environmental disasters and degradation, and violence.
We would expect that adaptation to the dangers of future climate change
would be added to this list of tasks of the modern state.
SEA-LEVEL RISE AND COASTAL SYSTEMS
One of the major concerns over coming decades and centuries is the
impact of SLR on coastal systems and human settlements near the
coast. I begin with the scientifi c background and projections and then
discuss the potential impacts.
The long-term movement in sea level since the last ice age is re-
markable. About 20,000 years ago, the earth reached a glacial maxi-
mum. At that point, global temperature was 4-5°C colder than today.
The level of the ocean was about 120 meters (400 feet) lower. If you
stood on today's east coast of Florida, the ocean would have been below
the horizon 100 miles away.
Sea-level rise has two major components: thermal expansion and
melting of terrestrial ice. Thermal expansion occurs because water den-
sity changes with different levels of temperature, salinity, and pressure.
On average, as the oceans warm, they will expand, thereby raising sea
level. This part of SLR is well understood and can be accurately modeled.
The oceans have been rising slowly since the last ice age. Current
estimates are that the rate of SLR is approximately 3 millimeters (0.1
inch) per year. Under standard climate-change projections, thermal ex-
pansion will raise the oceans by about 0.2 meters (8 inches) by 2100.
This is only slightly more rapid than the rate of SLR over the twentieth
century.
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The other major component of SLR is melting ice from glaciers and
ice caps, but the estimates here are highly uncertain. What most wor-
ries scientists is the vast quantity of water locked up in the three major
