U.S. carbon dioxide (CO2) emissions saw a yearly increase of 3.4 percent in 2018, according to preliminary estimates released Tuesday.



The rise represents the second-biggest yearly gain in over two decades, independent research provider the Rhodium Group said in a note. The figures are based on "preliminary power generation, natural gas, and oil consumption data." The increase was only surpassed by the 2010 figures when the economy was bouncing back from the global financial crash, it said.



Breaking the figures down, the transportation sector remained the largest source of emissions in the U.S. for the third year in a row, with "robust growth in demand" for both diesel and jet fuel offsetting a "modest" drop in gasoline consumption.



While a record amount of coal-fired power plants were shut in 2018, emissions from the power sector grew by 1.9 percent, the note said. This was down to natural gas replacing the majority of this lost generation and feeding the majority of growth in electricity demand.



The buildings and industrial sectors also showed "big year-on-year emissions gains." This was in part down to "unusually cold" weather at the beginning of 2018. The estimates in Tuesday's note refer to energy-related CO2 emissions only.