text: The first threshold question is: when were U.S. CO2 emissions from fossil fuel use last at 1 billion tons, the year 2050 target? From DOE historical statistics on energy consumption, it is possible to estimate that the United States last emitted 1 billion tons in the year 1910, when the nation's population was only 92 million people, per-capita income (in 2008 dollars) was only $6,196, and total GDP (also in 2008 dollars) was about $572 billionabout one-twenty-fifth the size of the U.S. economy today (see table 1).