WASHINGTON (Reuters) - The leading Democratic candidates all believe climate change is an existential threat to the planet and have vowed to bring U.S. greenhouse gas emissions down to net-zero by 2050.

FILE PHOTO: The Dayton Power & Light J.M. Stuart Station lights up the early morning sky on the banks of the Ohio River in Aberdeen, Ohio, U.S., September 13, 2017. REUTERS/Brian Snyder/File Photo

While the candidates have the same broad goals, they vary in their approaches.

JOE BIDEN

Joe Biden, former vice president under Barack Obama, touts a $1.7 trillion plan to set the United States on a course to achieve 100% clean energy and net-zero emissions by 2050. The plan calls for the installation of 500,000 electric vehicle charging stations nationwide by 2030, rejoining the United States to the Paris Climate Agreement, ending fossil fuel subsidies, and providing $400 billion for research and development in clean technology.

Biden’s plan sees at least some role for fossil fuels during the transition to a clean energy economy: it would invest money in carbon capture and sequestration, a potential lifeline to coal and natural gas-fired power plants.

Biden’s rivals have accused him of offering a weak plan that would not achieve decarbonization goals. They point out that during his time in the Obama administration, domestic crude oil production rose 77% and the United States lifted a decades-long ban on crude oil exports.

MICHAEL BLOOMBERG

Michael Bloomberg, a media billionaire and former New York City mayor, said last year he will give $500 million to a campaign coordinated with the Sierra Club and other green groups called Beyond Carbon, pressuring coal plants to shut and stop the growth of natural gas.

While he takes credit for shutting hundreds of coal plants, low natural gas prices have arguably played a bigger role in their shuttering than activism. Bloomberg fought to shut global coal plants as a U.N. special envoy for climate, a post from which he stepped down to enter the race.

Bloomberg would not ban fracking. He says it is vital for drilling oil and gas, but regulations are needed to stop leaks. His climate plan, on which he does not estimate a price tag citing the unknown future costs of green technologies, would halve U.S. carbon emissions in 10 years. He has also released the first plan to specifically tackle emissions from transportation. It leans heavily on making vehicles electric.

PETE BUTTIGIEG

At 38, Pete Buttigieg is attempting to win voters by reminding them that his generation faces the most risks from climate change. He has called for the United States to achieve net-zero emissions by the time he is 68 years old - 2050.

The former mayor of South Bend, Indiana, supports a national carbon tax and dividend, a method of directing revenues from fees on fossil fuels to families most affected by a transition to cleaner energy sources.

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A military veteran, Buttigieg has emphasized climate risks to security. He backs a “climate corps” to get thousands of young people working on building community resilience to extreme weather. He has also emphasized the role of local governments in combating climate change, proposing to hold a Pittsburgh Climate Summit to convene local leaders who have set their own plans to zero out emissions.

AMY KLOBUCHAR

Klobuchar, a U.S. senator from Minnesota, launched her 2020 campaign in the midst of a snowstorm in February, prompting Trump to take to Twitter to mock her for fighting global warming while standing in freezing temperatures.

Klobuchar was one of the early backers in the Senate of the Green New Deal and has vowed to use her first 100 days in office to issue executive actions to tackle climate change by restoring some Obama-era policies.

Playing to her strength as a Midwestern politician, she has called for boosting the Renewable Fuel Standard, a policy supported by corn-producing states like Iowa and Nebraska that require billions of gallons of ethanol in the nation’s gasoline supply. But Klobuchar, endorsed by the New York Times as the best of the Democratic field representing moderates, irked climate activists at the most recent debate in January calling natural gas a “bridge fuel” – a position that was popular for politicians more than a decade ago. Recent studies have shown that natural gas use has led to an increase in U.S. greenhouse gas emissions, in part because the fuel has a tendency to leak into the atmosphere from drill sites, compression stations, and pipelines before being burned.

Other candidates like Sanders, Warren and former New York City Mayor Michael Bloomberg have called for a ban on using natural gas in new buildings and a more rapid shift away from its use in power plants.

BERNIE SANDERS

“We need a president who welcomes their hatred,” U.S. Senator Bernie Sanders of Vermont says in his plan, referring to fossil-fuel executives he sees as blocking action on climate.

His plan, dubbed the Green New Deal after a resolution sponsored by progressives in Congress, would mobilize $16.3 trillion to generate all U.S. electricity from renewable sources by 2030 and create publicly owned utilities.

Gasoline-fueled cars would be phased out, while electric car-charging stations and public transport would get government support.

The plan would also ban new nuclear plants, currently the top source of carbon-free power, and the burying of carbon emissions from fossil fuels, a technique favored by the United Nations.

He and rival Elizabeth Warren have said they would ban fracking - a drilling technique that pumps water and chemicals into rock formations underground - nationwide, prompting the American Petroleum Institute to launch a campaign touting the benefits of oil and gas.

The Sunrise Movement, the influential youth climate activist group that has risen to national prominence, endorsed Sanders saying he “grasps the scale of the climate crisis.” But Republicans and some labor leaders worry his plan is too extreme and would hurt the economy.

TOM STEYER

Like Bloomberg, Tom Steyer is another billionaire who has a long track record of funding climate initiatives. The former hedge fund manager bankrolled NextGen America, an organization backing political candidates focused on climate change. Climate change features heavily in his multi-million dollar television ad campaign. At the last Democratic debate, Steyer said he would declare a climate emergency on his first day in office and positioned himself as the candidate most focused on climate change. He has proposed a complete reform of the U.S. tax system, putting a 1% tax on Americans with a net worth over $32 million and 2% tax on billionaires. His plan would use $2 trillion of tax revenue over 10 years to upgrade and green U.S. infrastructure.

ELIZABETH WARREN

U.S. Senator Elizabeth Warren of Massachusetts outlined a $3 trillion plan to usher in a clean energy economy and combat climate change. She has also woven efforts to fight climate change into her other policy platforms: her economic plan, for example, would encourage investment in green research, manufacturing and exports, and create a federal procurement program for American-made renewable or emission-free energy for federal and state use and export. Some of her plan would be funded by reversing Republican tax cuts that largely benefit businesses and the wealthy.

Her goal: 100% zero emissions for most new vehicles by 2030 and 100% zero emissions in electricity generation by 2035.

Like Sanders, Warren also promotes a fracking ban – a plan that may be difficult to execute without congressional support - and a halt on leasing federal land for drilling through executive action.

ANDREW YANG

Entrepreneur Andrew Yang said at the second presidential debate he would tackle climate change by paying people hit by rising seas and flooding to move to higher ground. His $4.87 trillion plan offers $40 billion in loans and subsidies to people who wish to relocate. Yang said his plan’s price tag pales in comparison to the costs of climate change’s health and environmental impacts. His plan sets a target of net-zero U.S. emissions by 2050. It calls for a modernization of the electric grid, debt forgiveness for rural electric co-ops to switch to renewables, and a carbon tax on polluters.