The Department of Energy released its greenhouse gas emissions data in July, and it shows that energy-related carbon dioxide (CO2) emissions rose by 213 million tons in 2010, after falling by nearly 500 million tons (or almost 9 percent) in the steep recession year of 2009. (See Figure 1.) The rise in CO2 emissions in 2010 represents a 3.9 percent increase. But hold on a moment: the economy didn’t grow by 3.9 percent in 2010—it only grew by 3 percent in real terms—which means that we lost ground on carbon-intensity last year. For most of the last decade, the economy grew faster than energy use, which meant that we were steadily improving our carbon intensity.
There’s a broader lesson here, shown in Figure 2 below, which shows the amount of energy generated from burning wood in the United States from 1900 to 1970, when the government discontinued the data series because the only people still getting energy from wood were the wood stoves in Vermont and such. (Amazingly, at the turn of the last century, the United States got nearly one-third of its energy from burning wood—over 5 billion cubic feet of wood a year in 1900. Who knew that moving to oil, gas, and coal actually saved forests.) What is especially notable about Figure 2 is the upward kink in the long-term trend, which coincides with the Great Depression. There’s no trick to understanding this: investment in technology and efficiency upgrades slow way down when the economy is bad. Economic growth turns out to be the precondition of energy efficiency improvements.
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