One Democratic political consultant, Rebecca Katz, said that climate has risen in importance in the 2020 race with the introduction of the Green New Deal, a congressional resolution calling for an aggressive mobilization to move the United States to renewable energy and eliminate greenhouse gas emissions. Mr. Inslee has praised the Green New Deal, as have a number of senators who are also running for president — Cory Booker, Kirsten Gillibrand, Kamala Harris, Amy Klobuchar, Bernie Sanders and Elizabeth Warren.

“The benefit of Inslee is that he actually has a record here,” Ms. Katz said. “There’s a lot of candidates who have kind of seen the light and are now for a Green New Deal, but Inslee has been talking about this issue for a long time.”

In a 23-minute speech on Friday to supporters who had crowded into a solar energy company warehouse south of downtown Seattle, Mr. Inslee spoke almost as much about optimism and hope as climate.

The belief that the nation can rise to the challenge of climate threats and push toward a zero-carbon energy system, he said — and do it with social justice and fairness — is crucial to the effort.

”We are an optimistic America that can do great things,” he said. “We know we can do hard things.” And under his presidency, he added, one of the first hard things would be ending special treatment for the fossil fuel industry.

“I have a message for the oil, coal and gas special interests — that gravy train is over,” he said.

Mr. Inslee is the first major-party politician from Washington State to run for president since Senator Henry M. Jackson, who was also a Democrat. Mr. Jackson was briefly a contender in 1976 before ultimately losing the nomination to Jimmy Carter, who won the general election that fall.

In a statement to the crowd about climate — though it seemed to be about Mr. Inslee’s candidacy as well — he said that timing was everything. “We have one chance to defeat climate change and it is right now,” he said. “And it is my belief that if you have one chance in life, you take it.”