Read the excerpt from "Climate Change: An Overview.” By the early twentieth century, carbon emissions from fossil-fuel burning reached 1 billion tons a year. Automobiles, airplanes, and domestic and agricultural energy demands all contributed to the rising trend. In the 1950s, scientists used a new generation of equipment to confirm that carbon-dioxide concentrations were doubling and that this would have the effect of increased temperatures. What chronology is described in this excerpt?