The Environmental Protection Agency released its Clean Power Plan in August, designed to control carbon dioxide emissions from coal-fired power plants, which scientists say are a major contributor to climate change. Some utility companies and lawmakers from coal-producing states immediately condemned the plan — which aims to reduce power-sector carbon emissions by 32 percent from 2005 levels by 2030 — and are challenging it in court. The plan is part of U.S. preparations for a November international conference on climate change in Paris. In the run-up to the conference, the United States also has forged carbon-control agreements with China and Brazil. Questions remain, however, about China’s commitment to the agreement and what heavy polluters India and Russia will do to control carbon emissions. Pope Francis also has weighed in, calling climate change one of the principal challenges facing humanity.