If the optimists are wrong, however, prepare for a shock. In a 2009 paper [PDF], Hall and his colleagues estimated that energy supplies with an EROI of at least 12 to 13 were required to support the trappings of modern developed nations, such as higher education, technological progress, and high art. Oil and gas production in the United States may have already fallen below that threshold, the paper says, and global production appears to be following fast.
The implications, according to Prieto and Hall, are sobering. In fact, Prieto believes he is already witnessing economic decline caused, in part, by petroleum's dwindling EROI. He sees it manifested in Spain's debt crisis. "Energy is the ability to do work. If we do not have more energy one year than the preceding year, we will hardly be able to grow," he says. "And, if there is no growth, the financial system collapses."