By Coral Davenport and Trip Gabriel, New York Times–

Democratic candidates promised unprecedented new action on climate change on Wednesday night in the first prime-time televised forum devoted to the issue in a presidential campaign, vowing to undo the Trump administration’s environmental policies, spend trillions of dollars to promote renewable energy and force companies to pay taxes or fees on carbon pollution.

The event featured the 10 leading candidates, who appeared in back-to-back interviews and never crossed paths on camera. But hovering over the event was the influence of Jay Inslee, the Washington governor who made the climate crisis the singular focus of his presidential bid before dropping out of the race last month. In laying out their agendas, several of the remaining candidates echoed ambitious proposals that Mr. Inslee first put out.

Senator Kamala Harris of California took a page straight out of Mr. Inslee’s playbook, making new vows to enact aggressive environmental policies that just a few years ago were voiced only by the most left-wing candidates. She called for outright bans on hydraulic fracturing, or fracking, for oil and gas, and on offshore oil and gas drilling.

She also called for ending the Senate filibuster, a century-old legislative institution, in order to overcome Republican opposition and push through new climate change laws.

“This is an existential threat to who we are,” she said of climate change.

Ms. Harris said she would consider changing dietary guidelines to reduce consumption of red meat, the production of which is responsible for a large portion of the world’s planet-warming emissions. She even said she would consider a national ban on plastic straws, while conceding that paper straws are trickier to sip from. “They still need to be perfected,” she said.

The three leading candidates in the polls — former Vice President Joseph R. Biden Jr. and Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont — were scheduled to appear later in the evening.

Ms. Harris and Ms. Warren were among six candidates who released climate plans this week, seeking to seize a political moment when concern over the planet’s future is a driving issue among Democrats.

More than half of the candidates have embraced the idea of putting a tax or fee on carbon dioxide pollution, the one policy that most environmental economists agree is the most effective way to cut emissions — but also one that has drawn intense political opposition. Around the country and the world, opponents have attacked it as an “energy tax” that could raise fuel costs, and it has been considered politically toxic in Washington for nearly a decade.

a man holding a kite while standing in the grass: Senator Elizabeth Warren’s plan calls for eliminating planet-warming emissions from power plants, vehicles and buildings over 10 years.© Elizabeth Frantz for The New York Times Senator Elizabeth Warren’s plan calls for eliminating planet-warming emissions from power plants, vehicles and buildings over 10 years.

Ms. Harris’s pledge to ban fracking, the controversial method of extracting oil and gas used across the country, would also be an aggressive new check on the fossil fuel industry, one that was never proposed by President Barack Obama or by Hillary Clinton, the 2016 Democratic presidential nominee.

Two other candidates who said they would support carbon pricing, Senator Amy Klobuchar of Minnesota and the former housing secretary Julián Castro, said they would not call for outright bans on fracking. But both said they supported limiting the use of natural gas. Mr. Castro, the former mayor of San Antonio, said that in that job, he supported fracking for natural gas as a “bridge fuel” designed to take the economy to cleaner forms of power.

“We’re now getting to the end of that bridge,” he said.

The town hall-style forum on CNN was a response to primary voters’ intense interest in climate change and follows a decision by the Democratic National Committee not to sanction a debate devoted to the subject, frustrating activists and some candidates.

A prime-time discussion about climate change was “20 years overdue,” Mr. Inslee said in an interview on Wednesday, adding, “I think we should attack Donald Trump on his weakest point, which is the environment, and this will help us identify our strongest candidate.”

Jeff Nesbit, executive director of Climate Nexus, a group focused on communicating the climate threat, said the forum reflected pent-up demand by a portion of the Democratic base to see global warming discussed in depth. Voters want “more than a scant, few minutes from TV news stars moderating general debates who ask questions like ‘Can Miami be saved?’ or ‘So, what’s wrong with the Green New Deal?’” he said.

But the seven-hour-long format may have challenged viewers’ stamina and frustrated those seeking clear contrasts between the candidates.

The parade of far-reaching plans on display, ranging in cost from $1.7 trillion to $16.3 trillion, was also certain to elicit Republican attacks. President Trump and his allies, who have sought to roll back Obama-era limits on planet-warming emissions, have been attacking the Democratic field as “socialists.” On Wednesday, the administration rolled back rules on energy-saving light bulbs.

“The Democrats’ radical approach to energy is to eliminate the use of all fossil fuels, which would kill more than 10 million jobs and inflict economic catastrophe across the country,” said Tim Murtaugh, a spokesman for President Trump’s re-election campaign.

The Democrats’ plans vary in costs and priorities but most have a similar aim: to reach carbon neutrality by 2050 — that is, reducing planet-warming carbon emissions so dramatically that the United States is eliminating as much as it emits.

The trillions in new spending the candidates have proposed would by and large go to similar priorities, like updating the country’s power grid and other energy infrastructure, installing electric vehicle charging stations and developing clean power like wind and solar.

While spending money is a solution that unites the candidates, they differ on where the money should come from. Ms. Warren calls for a 7 percent increase in the corporate tax rate. Mr. Sanders has said his plan would “pay for itself” by collecting tax revenue from high-paying new jobs and new fees and penalties from the fossil fuel industry.

The broad support for putting a price or tax on carbon dioxide is a remarkable change since the 2016 campaign, when Mrs. Clinton steered clear of embracing a price on carbon pollution, for fear that it would be attacked as an energy tax.

Ms. Harris was the first candidate at the forum to directly address the largest political hurdle for a president who hoped to enact such policies: the Senate filibuster.

Mr. Obama also sought to enact a sweeping climate bill that would have effectively placed a tax on carbon pollution, but it failed even when both chambers of Congress were controlled by Democrats because it could not overcome the 60-vote threshold required by the Senate’s filibuster rule in order to advance a bill through the chamber.

Mr. Inslee has called for abolishing the Senate filibuster — a move that would transform the way laws are made in the United States. Most of the presidential candidates have avoided calling for such a move, but analysts say that without it, their bold climate change plans — especially their calls for lavish spending — will remain unrealized.

But abolishing the filibuster could also make laws vulnerable to quickly being undone by a new Senate majority, leading to an unstable whipsaw effect as laws are signed by one president and quickly undone by another.

“I’m not going to be burdened by what the next president will do to reverse this,” Ms. Harris said.

Many of the candidates’ policies, including Ms. Harris’s, bear similarities to proposals championed by Mr. Inslee, who had released six detailed climate plans totaling over 200 pages.

Mr. Inslee dropped out after it became clear he was unlikely to qualify for the next primary debate, having failed to reach 2 percent support in enough polls. For that reason, he would not have been invited to the climate change forum, either. But analysts said his influence on the rest of the Democratic presidential field was clear.

“Jay Inslee wrote a super-set of climate policy options, and candidates are taking subsets of Inslee ideas,” said Kevin Book, an analyst with ClearView Energy Partners, a nonpartisan Washington research organization.

In a Democratic debate in July, Mr. Inslee assailed Mr. Biden’s $1.7 trillion plan for not being forceful enough in phasing out coal in line with what “the science tells us.”

On Wednesday, Mr. Inslee said Mr. Biden had called him a few days ago to suggest a policy conversation between their staffs. “All of us have to raise our ambitions, that includes the vice president,” he said, adding that their conversation was pleasant.

In her new climate proposal, Ms. Warren adopts Mr. Inslee’s plan to eliminate planet-warming emissions from power plants, vehicles and buildings over 10 years, and adds an additional $1 trillion in spending to subsidize that transition. The spending would be paid for, she said, by reversing the Trump administration’s tax cuts for wealthy individuals and corporations.

Ms. Harris’s plan, which calls for $10 trillion in spending over a decade, includes many of the same basic policy elements as those of her rivals: a blueprint to end fossil fuel pollution from electricity generation by 2030, a halt on new fossil fuel leases on public lands and the imposition of new regulations on vehicle tailpipe pollution.

Four other candidates — Ms. KlobucharMr. Castro, Senator Cory Booker of New Jersey and Mayor Pete Buttigieg of South Bend, Ind. — have also released climate change plans since Sunday.

Mr. Castro’s plan includes several ideas either directly adopted from or developed in consultation with Mr. Inslee, such as a plan to replace all coal-fired power generation with zero-emissions sources by 2030, and a proposal to marshal $10 trillion in federal, state, local and private spending on jobs associated with the transition to nonpolluting energy.

At least some echoes of Mr. Inslee’s proposals are also included in Mr. Booker’s plan, which calls for $3 trillion in spending to achieve a carbon-neutral economy by 2045, and in Ms. Klobuchar’s plan, which calls for reinstating Obama-era regulations on fossil fuel emissions to put the nation on track to a carbon-neutral economy by 2050.

Mr. Sanders has not explicitly taken up Mr. Inslee’s ideas. Instead, analysts said, he is trying to win over the progressive 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 has called for banning fracking to extract natural gas, and for halting the import and export of coal, oil and natural gas.

Mr. Buttigieg’s plan also makes no reference to Mr. Inslee. It calls for putting an unspecified price on carbon that will rise over time, and for quadrupling spending on clean energy research and development to $25 billion per year to achieve net-zero emissions by midcentury. Total federal spending would range from $1.5 trillion to $2 trillion, the Buttigieg campaign said.

Lisa Friedman contributed reporting.