Friends,
I first became aware of global warming in 1974, when I read
Paul Colinvaux's _Introduction to Ecology_ in a course on Human
Ecology that I took as an undergraduate at the University of
Michigan. I have since maintained an active interest in the
issue, and became a dedicated student of the literature in 1985.
In 1992, I received (along with my colleague Timmons Roberts) a
NSF grant to apply world-systems analysis to the question. Hence
I feel well qualified to speak on the matter.
Natural and dramatic fluctuations in climate are well
documented from ice cores, tree rings, and ocean sediment samples
going back over 250,000 years. Changes in solar output do indeed
accompany sunspots, and such changes are plausible causes for the
"little ice age" that Carl mentioned in his post. Further, this
long record of data shows that the global climate has jumped (and
dipped) as much as 10 degrees (f) in a single decade. These
flip-flops appear to have been jumps between different
"equilibrium" states that were prompted by alternative shut-downs
and restarts of the gulf stream in the Atlantic, which in their
turn were triggered by prior & gradually building complex
interactions between vegetation and polar ice sheets, which
collectively alter the reflectivity of the Earth's surface to
solar radiation.
Another key factor affecting the reflectivity of the Earth
to solar radiation is the composition of the atmosphere. The
chemistry of the atmosphere changes its clarity--its ability to
bounce solar energy back out into space. While the incoming
radiation spans the entire spectrum from UV through to Infra-Red,
it is the visible portion that passes most easily through the
atmosphere. This visible inflow does not bounce-back unchanged.
Instead, it typically gets absorbed by the surface rocks, soil,
and plants and changed into heat. Only then does it "bounce-
back", but now as heat, or Infra-Red radiation. Here things get
interesting. The "clarity" of the atmosphere to heat/Infra-Red
radiation is extremely sensitive to the percentage of the
atmosphere that is CO2. CO2 is OPAQUE to Infra-Red radiation.
That is, it absorbs light at those wavelengths, thereby trapping
heat. In general & on average, the atmosphere is 60% Nitrogen,
20% CO2, 8% Oxygen, & the rest misc. However, small changes in
CO2 translate into large changes in heat retention, a fact noted
as long ago as the 1890's, when the scientific plausibility of
global warming was first advanced.
Over the 200 years 1790-1990, measured levels of CO2 in the
atmosphere have risen 30%, with most of the increase occurring
since 1950, precisely matching the global extension of fossil
fuel technology throughout the periphery in order to expand
markets and increase automation. It is no coincidence that the
10 hottest years on record have occurred since 1985;
glaciers globally have been receding at unprecedented rates, both
plants and insects have been documented abandoning traditional
locations for cooler environments higher up on mountains and
further north, while diseases associated with the tropics have
been marching steadily northward (eg Dengue, Malaria).
This has been only a cursory skim over the top of the most
obvious theory and data. However I hope that this can serve to
alert many of you that the science, theory, and empirical support
for the reality of human-induced warming is solid, and backed up
by a thorough body of serious research. Should anyone wish more
information, I would be happy to prepare a lengthy bibliography
of sources upon request.
--Peace, Peter Grimes