evidence: This week, Scott Pruitt, Environmental Protection Agency administrator, who had said that human activity was not the primary contributor to global warming, acknowledged that it plays a role—but stressed the need to figure out exactly how much of one. [...] In addition, there is much more methane (a greenhouse gas 84 times more potent than CO2 in the short term) in the atmosphere than at any time in the past 800,000 years—two and a half times as much as before the Industrial Revolution. While some methane is emitted naturally from wetlands, sediments, volcanoes and wildfires, the majority of methane emissions come from oil and gas production, livestock farming and landfills. [...] In addition, the lower atmosphere (troposphere), which is absorbing the CO2 and expanding as it gets warmer, is pushing the boundary between the troposphere and the stratosphere upwards. If the sun’s radiation were the main factor responsible for Earth’s warming, both atmosphere layers would likely be warming and this would not occur.