Geoscience Reference
In-Depth Information
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Why Is Climate So Variable in the West?
El Niño has taught two lessons that will endure. h e i rst is that
large-scale variability such as El Niño is not a disaster, anomaly,
or cruel twist of fate; it is how Earth works. To mature and live
harmoniously in the Earth system, human culture must adapt
to Earth's rhythms and use natural variability to its advantage.
Michael Glantz,
Currents of Change
Climatologists in the American West have been carefully
recording daily observations of weather conditions for the past 150 years.
h ey have also monitored ocean conditions over recent decades, provid-
ing insights into the critical interactions between the Pacii c Ocean and its
overlying atmosphere. In this way, climate scientists have assembled many
seemingly unrelated observations into a larger picture that explains, at least
in part, why climate in the American West changes from year to year, decade
to decade, and perhaps over even longer timescales. h is chapter provides an
overview of the discoveries that begin to explain why climate is so variable in
the West—at least over the past century and a half.
where western climate patterns start
To understand what controls climate in the American West, we look i rst to
the region's neighboring body of water, the Pacii c Ocean, which is immense
by any measure: it contains half the water on Earth and covers over one-
quarter of the globe. In physical terms, the ocean is a vast heat engine as
well as a source of water for the western United States. Although the ocean
is 2.5 miles deep (on average), the temperature of the waters in just the top
300 feet or so is what af ects climate in the West by altering large-scale
patterns of atmospheric pressure and circulation, which are factors in the size
and movement of rain-bearing storms.
