Climate change futures: health, ecological and economic dimensions

THE PROBLEM:
CLIMATE IS CHANGING, FAST
The proposition that climate change poses a threat
because of an enhanced greenhouse effect inevitably
begs questions. Without greenhouse gases such as
CO 2
trapping heat (by absorbing long-wave length
radiation from the earth’s surface), the planet would be
so cold that life as we know it would be impossible.
For more than two million years, Earth has alternated
between two states: long periods of icy cold interrupted
by relatively short respites of warmth. During glacial
times, the polar ice caps and Alpine glaciers
grow; during the interglacial periods, the North Polar
cap shrinks, as do Alpine glaciers.
Figure 1.1 Simulated Annual Global Mean Surface
Temperatures
Up until the 20th century, these cycles were driven by
the variations in the tilts, wobbles and eccentricities of
Earth’s orbit — the Milankovitich cycles, named for the
Serbian mathematician who deciphered them. The
temperature changes from the industrial revolution on,
however, can only be explained by combining natural
variability with anthropogenic influences (Houghton et
al. 2001) (see figure 1.1). Recent calculations of these
long-wave cycles project that the current interglacial
period — the Holocene — was not about to end any
time soon (Berger and Loutre 2002).
Much of human evolution took place during this latest
glacial period; our ancestors survived the cold periods
and prospered during the warmer interregnums, particularly
the most recent span that encompassed the birth
and efflorescence of civilization. So, if the climate is
warming, what’s the problem?
16 | THE CLIMATE CONTEXT TODAY
The simulations represented by the band in (a) were done with only
natural forcings: solar variation and volcanic activity. Those in (b)
were done with anthropogenic forcings: greenhouse gases and an
estimate of sulphate aerosols. Those encompassed by the band in (c)
were done with both natural and anthropogenic forcings included.
The best match with observations is obtained in (c) when both natural
and anthropogenic factors are included.
These charts formed the basis for the IPCC’s conclusion that human
activities were contributing to climate change.
Image: IPCC 2001
Climate change may not be a threat to the survival of
our species, but it is a threat to cultures, civilizations
and economies that adapt to a particular climate at a
particular time. Through history, humans as a species
have survived climate changes and those groups that
made it through the adversity of “cold reversals” did so
by calling on their capacities to communicate, cooperate
and plan ahead (Calvin 2002). But many civilizations
have also perished when they could not adapt
fast enough. Societies adapt to their current conditions,
taking a gamble that those circumstances will continue
or change gradually. Never has this been more true
than in the recent past: The explosion of human numbers
and the miracles of modern economic development
have all taken place during the extraordinary climate
stability that has prevailed since the early 19th
century. The five-billion-person increase in human population
during that period occurred against the backdrop
of a climate that was neither too warm, too cold,
too dry, nor too wet. In the past, climate change has
been driven by the Milankovitch cycles, volcanic eruptions
and the movement of continents. Now, ironically,
thanks in part to the nurturing climate of recent centuries,
humanity has become a large enough presence
on the planet to itself affect climate. As the evolutionary
biologist E.O. Wilson put it, “Humanity is the first
species to become a geophysical force.”
In its Third Assessment Report in 2001 (Houghton et
al. 2001), the IPCC came to the same insight. The
report’s four primary conclusions were: Climate is
changing; humans are contributing to those changes;
weather is becoming more extreme; and biological
systems are responding to the warming on all continents