A historic landmark occurred last week. Scientists at a Hawaii mountaintop observatory reported that carbon dioxide buildup in the atmosphere reached 400 parts per million for the first time since the Pliocene Epoch -- 5 to 3 million years ago, long after dinosaurs died, but before early humans evolved.
Before the Industrial Revolution, atmospheric CO2 had averaged about 280 ppm for at least 800,000 years. But an upsurge of coal, oil and gas burning began a relentless increase in the "greenhouse gas" that forms a heat-trapping barrier in the sky, slowly warming the planet's surface.
If th3 CO2 buildup keeps climbing past 450 ppm, it may cross a "tipping point" that will trigger the worst dangers of global warming. Arctic ice will melt, raising sea levels and flooding many coastal cities. Storm severity will worsen, inflicting trillion-dollar nightmares akin to last year's Hurricane Sandy. Floods, droughts, wildfires, tropical diseases and other evils will torment humanity. Losses will be enormous.
The St. Louis Post-Dispatch said of the buildup:
"If it hits 450 ppm, the Earth's mean average temperature could rise by two degrees Celsius. At that point, climate catastrophe will be well underway. The polar ice caps will be all but gone. So will many coastal areas. Deserts will spread .... If the nations of the world continue emitting carbon dioxide at current levels, 560 parts per million will be reached by the end of the century. At that point, huge parts of many of the world's largest cities will be under water."
Former Vice President Al Gore, who won the Nobel Peace Prize for his climate crusade, said of the 400 ppm landmark:
"Every single day we pour an additional 90 million tons of global warming pollution into the sky as if it were an open sewer .... The accumulated manmade global warming pollution in the atmosphere now traps enough extra heat energy each day to equal the energy that would be released by 400,000 Hiroshima-scale atomic bombs exploding every single day."
So far, humanity shows little desire to reduce fossil fuel burning. Appalachia's coal reserves are near an end, but natural gas is surging and oil remains a pillar of the world economy. The U.S. Geological Survey proudly reported this month that oil and gas deposits under western states may be twice as high as former estimates.
One more dreary fact: Methane leaking into the sky by the gas-drilling boom and by melting of arctic tundra is an even worse greenhouse gas than carbon dioxide.
Most people don't notice that a slow-motion calamity already has started. But unless global warming is curtailed by a rapid expansion of renewable energy -- solar, wind, tidal, geothermal, biomass, etc. -- the entire world eventually will feel painful results.