Hang Gliding and Paragliding Volume 44 / Issue 1: January 2014 | Page 57

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pollen, carbon, captured atmospheric
gases, isotopes and, of course, amount
of precipitation. From all these factors
scientists can determine the average
atmospheric temperature, humidity
and pollution (volcanoes and widespread fires earlier than a few centuries ago).
There is another method of determining past climate that goes back
even further: drilling for mud/clay/
sediment cores in river deltas. The
debris load that a river carries down
each year undergoes a cycle, with the
amount of deposit varying according
to the amount of snowpack and rain.
The pollen deposits’ annual variation
lets the researchers separate the years
as they do in ice cores. The sediment
records correlate very well with the

509.682.4359
tree-ring and ice-core records.
The tale these records tell is that
our climate has always gone through
temperatu re cycles of several degrees,
at least for the past few hundred thousands of years. In fact, the reasons for
the cycles are mostly celestial. The
earth’s axis wobbles in space (and
changes on the earth itself) and its elliptical orbit around the sun expands
and contracts. The sun itself has some
cyclic behavior. Right now the earth is
tilted toward the sun (in the northern
hemisphere) when its orbit is furthest
away from the sun. This arrangement
avoids extreme variation of temperature from summer to winter, but at
some times in the past, the opposite
was true.
What seems clear is that there is

a 19,000-year, a 26,000-year and a
41,000-year temperature cycle. These
cycles are interposed on one another
to give us long-term climate patterns.
The changes are generally slow, but a
large volcano eruption can alter things
abruptly for a while (not to mention a
meteor impact). However, the last ice
age appears to have progressed very
rapidly, with permanent snow engulfing large areas of the North in just a
few years. The warning here is that
(positive) feedback systems can add to
the effects of the slow celestial cycles.
For example, a cooling earth may
experience a widespread snow that
lingers and reflects heat back so the
cooling of the atmosphere is hastened.
The opposite effect may also happen
if the normally ice-covered regions

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