Air pollution

Maine Gov. Janet Mills holds a 1-pound block of carbon to make her point as she talks about her decision to support a transmission project that would bring Canadian hydropower to Massachusetts residents, on Thursday, Feb. 21, 2019, in Portland, Maine. Mills spoke at the Portland Jetport before heading to the nation's capital to attend the annual National Governors Association winter meeting. She was accompanied by Director Angela Monroe of the governor's energy office and Greg Cunningham from the Conservation Law Foundation. (AP Photo/David Sharp)

FILE - This April 14, 2011 file picture shows the Glencore headquarters in Baar, Switzerland. Commodities giant Glencore says it will cap how much coal it mines amid shareholder pressure to reduce emissions of greenhouse gases. (AP Photo/Keystone, Urs Flueeler, file)

FILE - In this April 6, 2016 file photo, truck drivers stand among trucks on the highway from Brussels to Luxembourg, in Spontin, Belgium. The European Union has reached a tentative agreement on the first specific EU standards for trucks to get polluting CO2 levels down. A Tuesday, Feb. 19, 2019, agreement between negotiators from the European Parliament and member states says that such emissions will have to be 30 percent down by 2030 compared to today's levels. (AP Photo/Geert Vanden Wijngaert, File)

FILE - This June 3, 2014, file photo shows a panoramic view of the Paradise Fossil Plant in Drakesboro Ky. President Donald Trump's vow to save the coal industry will be tested this week when a utility board he appoints weighs whether to close a coal-fired power plant in Kentucky whose suppliers include a mine owned by one of his campaign donors. An environmental assessment by the Tennessee Valley Authority recommends shuttering the remaining coal-fired unit at the Paradise Fossil Plant in Muhlenberg County. The board could vote on Thursday, Feb. 14, 2019. (AP Photo/Dylan Lovan, File)

FILE - In this Jan. 19, 2019, file photo, U.S. Rep. Alexandria Ocasio-Cortez, (D-New York) waves to the crowd after speaking at Women's Unity Rally in Lower Manhattan in New York. Democrats including Ocasio-Cortez of New York and veteran Sen. Ed Markey of Mass. are calling for a Green New Deal intended to transform the U.S. economy to combat climate change and create jobs in renewable energy. (AP Photo/Kathy Willens, File)

Senate Majority Leader Mitch McConnell, R-Ky., walks to the chamber on the morning after House and Senate negotiators worked out a border security compromise hoping to avoid another government shutdown, at the Capitol in in Washington, Tuesday, Feb. 12, 2019. (AP Photo/J. Scott Applewhite)

FI LE - In this June 17, 2018, file photo, man fishes from the Battery City Park esplanade as temperature edge near 90 degrees in New York. The weather in New York City in a few decades will feel like how Arkansas is now. Chicago will seem like Kansas City and San Francisco will get a Southern California climate if global warming pollution continues at the current pace, a new study finds. (AP Photo/Bebeto Matthews, File)

Some thousands of students gather to join a march in support of more ambitious climate policies in The Hague, Netherlands, Thursday Feb. 7, 2019. Organizers of the demonstration say they want to send a wake-up call to politicians in the Netherlands who are wrestling with how best to rein in greenhouse gas emissions. (AP Photo/Michael Corder)

FILE - In this Monday, Feb. 22, 2016 file photo, trekkers pass through a glacier at the Mount Everest base camp, Nepal. One-third of Himalayan glaciers will melt by the end of the century due to climate change, threatening water sources for 1.9 billion people, even if current efforts to reduce climate change succeed, according to an assessment released Monday, Feb. 4, 2019. by the International Centre for Integrated Mountain Development. (AP Photo/Tashi Sherpa, file)