Parts Per Million vs. Price Per Gallon

Hey Mr. Green,
How shall we endure headlines about fuel costs at the expense of headlines about increasing atmospheric CO2? Does the public recognize "385 ppm of carbon dioxide" as well as it recognizes "$4 per gallon"? --Marvin in Glencoe, Maine

Most of us relate more easily to a $60 bill at the gas pump than parts per million, or ppm, of global-warming gases. Just look at history: Driving habits have changed largely in response to pain at the pump--not because of the growing body of knowledge about problems from tailpipe emissions. In the late 1970s and '80s, when gas prices represented an all-time high percentage of household income, gasoline consumption plummeted 12 percent. But in the following decade, as gas costs became a smaller percentage of household income, even the doubling of cars' fuel economy didn't keep demand from rising year after year.

While vehicle miles traveled and gas consumption have declined in recent years, Americans still burn 50 billion gallons more motor fuel per year, have 100 million more vehicles on the road, and drive them an average of 3,000 miles farther annually than we did three decades ago.