Greenhouse gas emissions in the United States appear to be on the rise again after years of decline. The Rhodium Group, a Lab partner, recently released preliminary estimates showing carbon dioxide emissions overall surged 3.4 percent in 2018, with the transportation sector leading the way as the largest source of emissions for the third year in a row. Interestingly, the bump in transportation emissions didn’t come from cars. Car travel increased compared to 2017, but gasoline consumption decreased. That’s in part because overall fuel economy in passenger cars is improving as engines become more efficient and electric cars become more popular. Instead, emissions from trucking and air travel helped contribute to the overall increase: Demand for both diesel and jet fuel increased about 3 percent in 2018.