Complicating Stephen Budiansky's thoughts on emissions and efficiency, here is Bjørn Lomborg:

Here's something to think about. Back in the early 1970s, the average American expended roughly 70 million British thermal units per year to heat, cool, and power his or her home. Since then, of course, we have made great strides in energy efficiency. As the Washington Post recently reported, dishwashers now use 45 percent less power than they did two decades ago, and refrigerators 51 percent less. So how much energy do Americans use in their homes today? On a per capita basis, the figure is roughly what it was 40 years ago: 70 million BTUs.

This surprising lack of change is the result of something economists call the "rebound effect." It's a phenomenon familiar to urban planners, who long ago discovered that building more roads doesn't ease traffic jamsit merely encourages more people to get in their cars and drive.

The underlying principle is a decidedly counterintuitive fact of life. You might think that learning to use something more efficiently will result in your using less of it, but the opposite is true: the more efficient we get at using something, the more of it we are likely to use. Efficiency doesn't reduce consumption; it increases it. 

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