Hot and getting hotter  In the rarefied air of Mauna Loa
Observatory in Hawaii, 11,141 feet above sea level, scientists
have charted the passing of a milestone that, if ignored,
heralds a future for civilization both tragic and chaotic.  I'm
referring to the concentration of carbon dioxide in the
atmosphere, which Charles David Keeling began monitoring in
1958. At that time, CO2 concentration was 313 parts per million.
We are now at 400 ppm and that is not good news.  Why is this
number so important?  For hundreds of thousands of years, prior
to the industrial revolution, CO2 — the principal greenhouse gas
that holds heat in our atmosphere — never rose above 300 ppm.
The last time Earth's CO2 was 400 ppm was during the Pliocene
era, some 3 million years ago, when sea levels were 49 to 82
feet higher.  Because of the higher level of greenhouse gases,
average global temperatures have risen 1.4 degrees Fahrenheit
over the past century. That seemingly small increase in
temperature is already showing up in the for