We want to encourage people to evaluate their carbon footprints and reduce them to a "sustainable" level. How many tons of greenhouse gas emissions per person is that?

—Dick Mearns in Greensboro, North Carolina

The Intergovernmental Panel on Climate Change warns that humanity must cut its total greenhouse gas emissions by at least 40 percent by 2050 to escape disastrous overheating. So the world greenhouse gas emissions average of 5.4 tons a person per year would need to drop by 2.2 tons. U.S. residents, however, would have to cut their emissions massively from their 23 tons per capita just to match everybody else in the world.

How do we accomplish this? Well, for household emissions—about half the U.S. total—the EPA provides a calculator. You input data representing your current emissions and then choose from a list of potential actions to reduce them (you can see results from each action). I punched in numbers for your city and believe that a typical household there can halve its emissions. Address your electricity use by switching to green power. Drive a car that's twice as efficient as the average vehicle today, and drive half as much. Doable? After going solar and carless, and installing an efficient furnace and double-glazed windows, my own household is now at 1 ton per person. 

But what about all those other tons you emit, like, say, on a coast-to-coast flight, which accounts for about 600 pounds of emissions per seat? You could purchase carbon offsets for that flight (at about $20, they're surprisingly cheap).—Bob Schildgen