Democratic candidates are expected to trumpet their plans when they appear on a CNN climate change forum on Wednesday. Here are three important things to know about their job claims.

The estimates are rough, at best

Most of the job-creation claims that come with Democratic climate plans are vague.

Senator Cory Booker of New Jersey unveiled a plan this week he said will create “millions of jobs where they are needed most.” Beto O’Rourke, the former Democratic congressman from Texas, promises that his plan to inject $5 trillion into clean energy infrastructure and research “will create jobs, support communities, and strengthen our economy.” Senator Amy Klobuchar of Minnesota on Tuesday released a package that includes $1 trillion to modernize energy infrastructure and “create good-paying union jobs.”

Mr. Biden, Ms. Warren, Mr. Castro , Mr. Buttigieg and Mr. Sanders have attached specific numbers to their promises. But the candidates often arrive at their numbers in very different ways.

T.J. Ducklo, a spokesman for Mr. Biden, said the former vice president’s estimate of “10 million well-paying jobs in the United States” was based on several studies linking infrastructure spending with job creation, including a Council on Economic Advisors study that found every $1 billion in highway spending translates into 13,000 jobs. Mr. Biden’s plan calls for $1.7 trillion in federal spending over 10 years into clean energy, which suggests a possible 22.1 million jobs.

But Mr. Ducklo said the campaign chose to cite a more conservative number, in part because much of the spending under Mr. Biden’s plan would go toward research, and also because the job-multiplier studies were conducted in an economy in recovery, resulting in more jobs per dollars spent.

Ms. Warren is the only candidate to detail how she intends to pay for her proposed $1.5 trillion clean energy investment: an increase of 7 percent in the corporate tax rate. She is also the only one who commissioned an independent economic analysis, which found the plan would lead to 1.2 million new jobs in the coming decade.

Jon Erickson, a professor of sustainability policy and science at the University of Vermont who advised Mr. Sanders’s campaign, said the senator’s prediction of 20 million jobs was based on a widely used economic modeling tool. Mr. Erickson said he had run simulations based on all the ways Mr. Sanders intends to spend $16.3 trillion over 15 years, from wind-power development to weatherizing homes, and added up the jobs that were likely to created both directly and indirectly.