“You may remember Gov. Jay Inslee said, ‘Let’s get tough on this,’” said Senator Elizabeth Warren of Massachusetts, as she laid out a new plan that she said had been influenced by her former rival. In addition to proposing $3 trillion in spending on environmental initiatives, Ms. Warren also responded “Yes!” when asked by a moderator, Chris Cuomo, if she would support a carbon tax — a measure she had not spelled out in her official policy proposal.

Senator Bernie Sanders of Vermont, who has not explicitly taken up Mr. Inslee’s ideas, said, “We are proposing the largest, most comprehensive program ever presented by any candidate in the history of the United States.” Mr. Sanders has sought to win over the liberal wing of the Democratic Party with a plan that takes its name from the Green New Deal and has the biggest price tag of all the candidates’ proposals — $16.3 trillion over 15 years. He is one of the few candidates who has not called for a carbon tax, however.

Former Vice President Joseph R. Biden Jr., whose team called Mr. Inslee’s staff earlier this week to set up a time to talk about policy ideas, and whose official policy plan does call for a carbon price, sought to position himself as a seasoned international leader on an issue that is fundamentally global in scope. While the United States is the world’s largest historic polluter of greenhouse gases, it today produces about 15 percent of total global emissions, and experts have said it is impossible to solve climate change without international curbs on emissions.

In the Group of 7, “I know almost every one of those world leaders,” Mr. Biden said, adding, “If I was present today, I would be — there would be no empty chair,” referring to a recent gathering at which Mr. Trump skipped a meeting on climate change.