<human>:  When did the United States become the world’s largest emitter of greenhouse gases?
<bot>: The United States became the world’s largest emitter of greenhouse gases in the early 1980s. The United States had been a relatively minor emitter of greenhouse gases until the late 1970s, when the use of fossil fuels began to increase rapidly. In the early 1980s, the U.S. economy experienced a major economic boom as a result of the oil shocks of the 1970s. This led to an increase in energy consumption and an increase in greenhouse gas emissions.