Biden believes action must be taken on global warming. As a senator, he co-sponsored the Sense of the Senate resolution calling on the United States to take part in the United Nations climate negotiations and the Boxer–Sanders Global Warming Pollution Reduction Act, the most stringent climate bill in the United States Senate. He wants to achieve a carbon-free power sector in the U.S. by 2035 and stop emissions completely by 2050. His program includes reentering the Paris Agreement, nature conservation, and green building. Biden wants to pressure China and other countries to cut greenhouse gas emissions, by carbon tariffs if necessary.