The one thing that can be said about the
earth's climate is that it's always changing!!
There are many factors that control the climate.
The system is what we call a complex system. This
means that a small change in some input such as
the luminosity of the sun can cause a major shift.
One way to think about the climate system is to
envision a system that is dynamically unstable but
at a quasi equilibrium...imagine a ball at the
very top of a slope such that at any location
around where the ball is resting is downhill.....
Now if no perturbation occurs, then the ball stays
at equilibrium and does not move... now imagine a
butterfly cruises by....the effect of the slight
wind is to give the little ball a little push!! it
is a VERY VERY VERY small push... but it is enough
to get the ball moving...and as soon as the ball
moves a tiny amount, it is going downhill... and
as it goes down, it now picks up momentum due the
gravity... the ball rolls all the way down the
hill.... and ends up 100's of yards from where it
started... now if you think about it, that little
butterfly did this!!!??? Well, yes and no... the
butterfly was the tiny PERTURBATION that allowed
the ball to seek a new minimum energy
configuration in the gravitational field of the
So this is just an analogy ...
the idea is that small perturbations can produce
drastic changes when one deals with a complex
system of which climate on any planet but
especially earth is an ARCHTYPICAL
The quaternary ice ages seem to
correlate with the amount of solar energy the
earth gets... it is a little variable because the
earth wobbles on its axis and its axis also
processes... and the eccentricity of the earth's
orbit around the sun changes a little bit... this
is called ASTRONOMICAL FORCING and ice ages are
related to that in large part.
type of forcing has to do with the composition of
the air.... methane and carbon dioxide are good
trappers of IR radiation... so when visible NOT IR
radiation from the sun heats the earth surface,
some of that energy is re- radiated in the IR part
of the spectrum... now THAT IR energy is absorbed
by methane and CO2 and hence is trapped
by the earth.....
The concentration of
CO2 has gone up significantly since the
industrial revolution. Complicated models of the
earth atmosphere that have been developed by
advanced scientists over the past 80 yearsrs with
increasing sophistication show that as the
CO2 content increases, temperature
average of air will go up.
summarize...climate is a complex system and
reducing a complex system to a linear one is a big
mistake....but having said that, the current
heating of earth especially in 20 and 21 century
is very likely due in significant amount to