Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 338

forecasts of possible future Greenland melt under a variety of IPCC SRES scenarios.
Taking the high IPCC climate change scenario, with carbon dioxide rising to some
1000 ppm up to the year 2200 and then stabilising (assuming it is not pushed higher
still by other surprises from other - non-fossil - carbon pools), the Greenland ice cap
will disappear over the next 2000 years (although there might be a small amount of
ice remaining on top of its eastern mountains). This melt alone will raise sea levels
by 6.5 m; although should this happen then sea-level rise will be higher than this due
to thermal expansion and other contributions from Antarctica (Alley et al., 2005).
Although our understanding of the Greenland ice cap is better than that of Ant-
arctica, our knowledge is still far from complete. The above 2000-year scenario is
largely based on melt factors. However, there are other mechanisms that serve to
release water from Greenland ice. One of these is increased glacier movement. In
2006 it became apparent from satellite images that glacier movement had increased
more than had previously been thought. It was already known that glaciers near the
coast had been moving faster, but the new satellite data showed that there had been a
marked increase some way inland and so the flow rates of Greenland's largest glaciers
had doubled in the 5 years since the beginning of the 21st century. This in turn means
that Greenland's estimated loss of ice mass has increased from a little more than 50
km 3 year − 1 to in excess of 150 km 3 year − 1 . The mechanisms behind this change are
thought to include removal of the formerly stable glacier ends (so reducing the glacier
ends' buttressing effect) and percolation of meltwater from the top of glaciers through
to their bases, so lubricating them (Dowdeswell, 2006; Rignot and Kanagaratnam,
2006). Consequently the IPCC 2001 and the US Geological Survey estimates (Table
6.3) will need revising and so the IPCC's next assessment report (with AR5 Working
Group I reporting in 2013 and Working Groups II and III reporting in 2014) may
well contain increased estimates for sea-level rise. These will be at the high end of
the predicted range, albeit with similar or lower estimates for sea-level rise at the low
end. (The latter, possibly lower, AR5 sea-level rise estimates are probable due both to
scientific uncertainty and the realization that the global economic slump beginning
in 2009 could be part of a longer-term trend that reduces greenhouse emissions and
hence 21st century warming.)
Such a remote future may seem to have little bearing on present-day life. Yet even
a small proportion of this long-term rise would in the shorter term have a significant
effect on humans and human-managed ecosystems in the present, and on land that
we currently consider that we will utilise indefinitely (from our human perspective).
What we have inherited from the past we largely expect to either use, or have its
use evolve, in the future. Today much of our infrastructure had its practical day-to-
day foundations laid centuries ago. For example, much of Europe's rail network was
established well over a century ago; in Britain Brunel's bridges are still being used
today. Much of Europe's principal road networks were established centuries earlier
still. Yet again, the geographical location of many of humanity's major settlements
were established thousands of years ago. But consider a future a thousand years
hence. London, for instance, would either be submerged or protected, either as an
island or as part of the south-east region of England, needing hundreds of kilometres
of towering sea defences scores of metres high. London would not be alone. New York,
Washington and indeed many of the Earth's major urban centres would need similar