Climate change futures: health, ecological and economic dimensions

20 | THE CLIMATE CONTEXT TODAY
Wholly new types of events are also occurring, such
as the twin Christmas windstorms of 1999 that swept
through Central Europe in rapid succession (with losses
totaling over US $5 billion; RMS 2002), and the first
ever hurricane recorded in the southern Atlantic that
made landfall in Brazil in early 2004.
CLIMATE PROJECTIONS
Over the next century the IPCC (Houghton et al.
2001) projects the climate to warm some 1.4-5.4°C
(or 2.5-10°F). Multiple runs of climate models suggest
that we may have vastly underestimated the role of
positive feedbacks driving the system into accelerated
change; and an ensemble of models extends the
upper end of the range to 11°C (20°F) and variability
becomes even more exaggerated (Stainforth et al.
2005). Andreae et al. (2005) project that a decrease
in “cooling” sulfates also raises projections to 10°C
(18°F). All the ranges are based on estimates as to
how society will respond and adjust energy choices,
as well as uncertainties regarding feedbacks.
(“Negative” feedbacks help reinforce and bind
systems, while “positive” ones contribute to their
unraveling.)
Projections from recent observations (Cabanes et al.
2001; Cazanave and Nerem 2004, Church et al.
2004) have been made for sea level rise (SLR), and in
the absence of collapses of ice sheets, SLR by the end
of the century will be 1 to 3 feet (30-90 cm). With
accelerated melting of Greenland and Antarctica ice
sheets (De Angelis and Skvarca 2003; Scambros et
al. 2004; Domack et al. 2005), these may be significant
underestimates (Hansen 2005).
CHANGES IN NATURAL MODES
Climate change may be altering oscillatory modes
nested within the global climate system. The El
Niño/Southern Oscillation (ENSO) phenomenon is
one of Earth’s coupled ocean-atmospheric systems,
helping to stabilize climate through its oscillations and
by “letting off steam” every three to seven years.
Warm ENSO events (El Niño) have in the past created
warmer and wetter conditions overall, along with
intense droughts in some regions. ENSO events are
associated with weather anomalies that can precipitate
“clusters” of illnesses carried by mosquitoes, water
and rodents (Epstein 1999; Kovats et al.1999) and
property losses from extremes tend to spike during
these anomalous years as well. Climate change may
have already altered the ENSO phenomenon (Fedorov
and Philander 2000; Kerr 2004; Wara et al. 2005),
with current weather patterns reflecting the combination
of natural variability and a changing baseline.
In Asia, the monsoons may be growing more extreme
and less tied with ENSO (Kumar et al. 1999), as
warming of Asia and melting of the Himalayas create
low pressures, which draw in monsoons that have
picked up water vapor from the heated Indian Ocean.
The North Atlantic Oscillation (NAO) is another climate
mode and the one that governs windstorm activity
in the Northeast US and in Europe. Global warming
may also be altering this natural mode of climate variability
(Hurrell et al. 2001), affecting winter and summer
weather in the US and Europe, with implications
for health, ecology and economies (Stenseth et al.
2002).
THE CHANGING
NORTH ATLANTIC
The overturning deep water in the North Atlantic
Ocean is the flywheel that pulls the Gulf Stream north
and drives the “ocean conveyor belt” or thermohaline
circulation. Melting ice and more rain falling at high
latitudes are layering fresh water near Greenland.
Meanwhile, the tropical Atlantic has been warming
and getting saltier from enhanced evaporation. This
sets up an increased contrast in temperatures and pressures.
The composite changes may be altering weather
systems moving west and east across the Atlantic.
These changes could be related to the following:
• Swifter windstorms moving east across to Europe.
• Heat waves in Europe from decreased evaporation
off the North Atlantic.
• Ocean contrasts helping to propel African dust
clouds across to the Caribbean and US.
• It is possible that more hurricanes will traverse the
Atlantic east to west as pressures change (and as
the fall season is extended).
• The layering of freshwater in the North Atlantic in
contrast to warmer tropics and mid-latitudes may be
contributing to nor’easters and cold winters in the
Northeast US.
During the 1980s and 1990s, the two air systems
(North and South) tended on average to be locked in
a “positive phase” each winter. Modeling this interplay,
Hurrell and colleagues (2001) found that Earth’s
rising temperature — especially the energy released
into the atmosphere by the overheated Indian Ocean
— is affecting the behavior of this massive atmospheric
system known as the NAO.