25.18% of U.S. greenhouse gases are being emitted by only 43 firms, according to figures tabulated by the Political Economy Research Institute (PERI), from corporate filings with the U.S. Environmental Protection Agency, as of the latest available year, which was 2011.
PERI, which is sponsored by the Economics Department at the University of Massachussetts at Amherst, lists the largest 100 emitters at its website.
Even just the top ten emitters account for 12.05% of U.S. greenhouse gases. In order, from the top, they are:
1: American Electric Power, 1.94%
2: Duke Energy, 1.89%
3: Southern Co., 1.76%
4: U.S. Govt., 1.16%
5: Berkshire Hathaway, 1.06%
6: Ameren Corp., 1.01%
7: Luminant Generation Co., 0.92%
8: FirstEnergy, 0.79%
9: AES, 0.76%
10: Xcel Energy, 0.76%
Almost all of the top 100 emitters are oil, gas, coal, and electric companies. For example, Warren Buffett's Berkshire Hathaway's chief emitters include its power plants, and petroleum and natural gas systems. Buffett has personally endorsed construction of the Keystone XL Pipeline, which would transport the world's highest carbon-gas-generating tar-sands oil (half of which is owned by the Koch brothers), from Alberta Canada to the Koch brothers' Texas Gulf Coast refineries, for shipment to Europe and Latin America. Buffett doesn't much care about global warming, and so he doesn't want governments to clamp down against global warming. Evidently, people in the future can just roast, for all he cares. He doesn't deny that 97+% of climatologists say that the biosphere is heating up and that humans are causing it to happen. His main concern is to make money from it. Similarly, he profited enormously from the taxpayer bailouts of Wall Street. (He bought a large chunk of Goldman Sachs right after the crash but before the bailouts. He got a special deal from the bank, which was then in hock to the U.S. Treasury, and he profited greatly from the bank's bailout by taxpayers.) Buffett has endorsed Hillary Clinton for President. Ms. Clinton, Wall Street's favorite Democrat, is one of the few Democrats who also worked behind the scenes to weaken anti-global-warming regulations, and to speed up development of oil and gas (including fracking). So, she's his type of "Democrat": a liberal-speaking actual conservative.
But most of these companies are clearly Republican: "drill, baby, drill." For example, the Koch brothers' firm, Koch Industries, is #27 on this list, and generates 0.36% of U.S. greenhouse gas emissions. The Kochs are additionally #14 on PERI's list of "Toxic 100 Air Polluters" (which measures toxins put into the air). The top five on that list, in order, are: Precision Castparts, E.I. du Pont de Nemours, Bayer, Dow, and ExxonMobil. ExxonMobil is also #14 on the greenhouse-pollution list, PERI's "Greenhouse 100 Polluters." So, there is some crossover between those two lists, but not much.