13. Conclusion (Climate change)
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This article is from the Climate Change FAQ, by Jan Schloerer jan.schloerer@medizin.uni-ulm.de with numerous contributions by others.
13. Conclusion (Climate change)
We need to know just about everything. ...
Is climate system modelling the ultimate example of hubris,
or, by chopping away at areas of ignorance, will we truly
improve our predictive capability ?
David Rind, Nature 363 (1993), 312
Current climate models tend to predict gradual climate change. This
is no guarantee against unpleasant surprises. Climate models as well
as the knowledge fed into the models are far from perfect [IPCC 95,
p 416-8, chapters 2, 4-6, 9-11] [Morgan] [Wielicki]. Rapid changes in
atmospheric circulation, of ocean currents, in ecosystem functioning,
or in the West Antarctic ice sheet's behavior may not be likely,
yet such risks can, at present, neither be excluded nor quantified.
[IPCC 95, p 45-6, 213, 304, 389, 525, 527-8] [Morgan]
Vice versa, sudden climatic shifts during the last ice age [IPCC 95,
p 177-9] [Keigwin 95] do not imply that similar shifts must necessarily
happen in the near future: during glaciation the ice sheets were much
larger and less stable than they have been for the past 10,000 years.
Past climates help to understand the climate system's workings, but
they do not readily reveal what to expect. Our climate seems to be
headed for a "warm atmosphere-cold pole combination" which may be
unique in earth history. No completely satisfactory geologic analog is
known [Crowley & North, chapter 14] [Eddy, p 17-27, 39-71] [Overpeck].
Much of the public debate focuses on warming, an admittedly likely
reaction of the climate system. Disturbing earth's radiation balance,
however, may change the climate in a host of other potentially serious
ways. Warming need not even be the practically most relevant part
of the response. This is why many climatologists prefer the term
`climate change' over `global warming'.
For example, spatial and seasonal patterns of precipitation, evapora-
tion, soil moisture and river runoff may shift. These in turn may
affect agriculture and freshwater availability, which are critical
for many poor countries and a potential source of migrations and
conflicts. Cloud patterns, ocean currents, atmospheric circulation
or the distribution of extreme weather events may change. Terrestrial
and marine life will be affected and may in turn affect the climate
via changes, for instance, of carbon storage, evaporation, or albedo
[IPCC 95, chapters 9-10]. The risk of rapid climate change is linked
to many other problems of concern, like population growth, poverty,
loss of biodiversity, or stratospheric ozone depletion.
Building a balanced public perception of the risks posed by climate
change is difficult. There is an almost irresistible temptation
to view extreme weather events, like droughts or storms, as signs
of climate change, even if they are well within the limits of natural
variability. At the same time, gradual change tends to go unnoticed.
Natural climatic variability can lead to temporary coolings; these
would be perceived as all-clears by many. We are up against a long-
distance race and tend towards a sprinter's outlook. [Maunder, p 75]
Human-made greenhouse gases and aerosols will change our climate.
There is no free lunch, we cannot alter earth's radiation balance
for nothing. It is uncertain by how much, how swiftly and with what
twists the climate will change. This is dubious comfort, since
uncertainty cuts two ways. The present best estimates may well
overstate the risk, but they may as well understate it. Climate
change resembles a gamble with high stakes.
Current knowledge of the carbon cycle suggests that atmospheric CO2
will respond sluggishly to CO2 emissions changes [IPCC 95, p 82-5,
323]. The response of the climate system to a given CO2 level takes
decades or longer. Barring surprises, the lag time between changes
in CO2 emissions and their eventual effects on climate is very long.
It is an open question how soon the uncertainties can be narrowed
down, and whether climatologists will be able to predict details
reliably before they start to happen in the real world [IPCC 95]
[Morgan]. There is a natural inclination to wait and see until
we know what we shall have to face. By then it may be too late.
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