president donald trump follow campaign pledge pull unite state global pact fight climate change source brief decision tell reuters wednesday u.s. carbon emissions fell last year 24-year-low expect continue decline next decade power company keep shut old coal plant generate electricity natural gas renewables u.s. energy information administration project total carbon dioxide co2 emissions energy consumption would fall 5,135 million metric tons 2017 5,171 million metric tons 2016 low since 1992. factbox u.s. carbon emissions see decline next decade