The great Thomas Schelling, a Nobel Laureate in economics, writes on global warming (that link will be available until Marhc 2nd or so):
The popular guessing game -- do we see a greenhouse "signature," can we
identify a clear "signal" in the "noise"? -- is probably premature. The
history of climate shows that sudden changes of global atmospheric
temperature have occurred. There are random or "chaotic" influences on
climate. El Niño is an example; volcanic emissions are another. There
are anthropogenic (man-made) influences besides greenhouse gases:
Aerosols of dust and, especially, sulfur emissions can block incoming
sunlight. Urbanization can produce "heat islands" that affect
temperature estimates. Finally, most of the globe is ocean; the
specific heat of water is great relative to air, and the oceans act as
a huge cooling reservoir that delays by perhaps decades the appearance
of atmospheric warming. The issue is not whether we can discern a
signal in the noise, but discern a signal among other signals.
So the recent temperature record is unlikely to be conclusive on the
cause of the warming. Greenhouse warming is not clearly established by
the temperature record nor is it in any way ruled out. We may see the
greenhouse signal clearly in another decade or two. Meanwhile we have
to rely on what science can tell us.
He goes on to tell us that the scientific community's consensus is that there is overwhelming evidence that the globe is warming: it's not a question of if but why it is occurring, how much will the globe warm, for how long will it last, and what are the consequences and benefits (that's where economists have chimed in).
In the limit, I suppose, things could get so bad that, in the future, the earth becomes another Venus:
Earth is unique in our solar system for its temperature range, and greenhouse gases are to be thanked. Venus has so much greenhouse atmosphere that water can't exist as liquid, Mars so little
that water can't exist as liquid. That carbon dioxide molecules absorb
infrared radiation has been known for a century. The earth's atmosphere
is transparent to most solar radiation; but as the earth, warmed by
daylight sun, radiates energy back into space it does so in the
infrared part of the spectrum, and the carbon dioxide absorbs some of
it and gets warm. Citrus growers in California and Florida use smudge
pots (ceramic tubes of burning crude oil) to produce on a clear still
night a blanket of carbon dioxide that captures some of the heat
radiating from the ground and keeps fruit from freezing.
Being a great economist, he realizes that as things change, people adapt:
But the uncertainties are daunting: The best the IPCC (The Intergovernmental Panel on Climate Change) can do is give us
a range of possible warmings for any given increase in carbon dioxide
concentration. And the upper bound of that range has been, for two
decades, three times the lower bound -- an enormous range of
uncertainty. On top of that are the uncertainties of what the change in
temperature will do to climates around the world. And on top of that
are the uncertainties of what those climate changes may do to the
worlds we live in, and what people will be able to do to adapt
successfully to what change is allowed to occur.
At dinner last night, colleagues and I discussed at how warm it has been up here in southern Minnesota - last Friday's weather notwithstanding - over the past few years. In my childhood, growing up in Northwest Iowa, I recall that at least once a year, we'd get a cold snap that seemed to last about 2 weeks, where temperatures would not rise above zero. That doesn't happen anymore. But there are places on this globe where it is bone-chilling cold.
But neither this anecdote nor the scientific evidence are proof-positive that we should dismantle or even slightly limit our economic growth engines to cool the earth back to "normal," whatever "normal" is in this case. Doing so may well make people worse off than otherwise. Coyote has more thoughts here.
