(CNN) A series of top Democratic presidential candidates have released sweeping plans to combat climate change over the last two weeks, putting the issue front and center ahead of CNN's climate crisis town halls on Wednesday night.

Although the overarching themes of each plan are similar -- all candidates lay out how they believe combating climate change is one of the most pressing issues facing the country -- there are marked differences within each proposal, as the candidates compete to distinguish themselves as the most focused and most willing to spend trillions to stop and reverse global warming.

Key differences are especially clear in how each candidate will pay for their plans. While some candidates argue they will fund the massive increase in federal spending by cracking down on polluters or instituting a carbon tax, others pledge to end tax breaks to fossil fuel companies and alter the tax code to ensure the wealthiest in the United States pay more. Some candidates endorse all of the above.

The climate crisis is a preeminent issue in the Democratic nomination fight, with polls showing it among the top -- if not the top -- issue on the minds of Democratic voters. A report by the UN Intergovernmental Panel on Climate Change warned recently that the planet has only until 2030 to stem catastrophic climate change.

Many of the candidates are also looking to tie themselves to former Washington Gov. Jay Inslee, the Democrat who centered his presidential campaign around climate change before he dropped out in August. Inslee met with Massachusetts Sen. Elizabeth Warren to discuss her plan, which expressly embraces portions of Inslee's detailed proposals, and former Housing and Urban Development Secretary Julian Castro's campaign touted its work with Inslee's team on its proposal.

Joe Biden

Former Vice President Joe Biden released his climate change plan earlier this summer, laying out a plan that pledges to go further than President Barack Obama's administration on climate, but is not as sweeping as the Delaware Democrat's more liberal opponents.

Biden's plan would dedicate $1.7 trillion to eliminate greenhouse gas emissions by 2050, end fossil fuel subsidies and ban new oil and gas permits on public lands. Biden does not outright support the Green New Deal, but his plan does tout the former vice president's support of elements of the plan that has been near universally endorsed by the left of the Democratic Party.

Biden, along with all of his Democratic opponents, supports rejoining the Paris climate accord, a sweeping multi-national climate agreement that President Donald Trump left early in his administration.

"Science tells us that how we act or fail to act in the next 12 years will determine the very livability of our planet," he said. "That's why I'm calling for a clean energy revolution to confront this crisis and do what America does best -- solve big problems with big ideas."

Bernie Sanders

Where Biden's plan was scaled back, Bernie Sanders ' plan released in August was massive: The Vermont senator called for $16.3 trillion in spending, comparing the task of combating climate change to a World War II-style mobilization of almost every sector of the economy.

The Sanders proposal's goal of reaching 100% renewable energy for electricity and transportation by 2030 matches the timeframe set by the IPCC, which outlined the dire consequences of global warming -- and what it would take to reverse them --in a 2018 report.

That timeline, however, is significantly faster than many of Sanders' opponents.

Sanders said his plan would create 20 million jobs in the transition away from fossil fuels despite imposing a ban on energy extraction, including fracking and mountaintop coal mining. He would also pursue civil and criminal cases against companies that concealed institutional knowledge of the dangers their products posed to the environment.

"Climate change cannot only be addressed by the United States. It is a global issue," Sanders said last month in Iowa. "But my promise to you is, instead of ignoring this issue as Trump does, I will help lead the world in bringing countries together to address the issue."

Elizabeth Warren

Warren , the other leading progressive hopeful, has made the most explicit overtures to Inslee, adopting on Tuesday significant portions of his plan after the two met.

But the Massachusetts senator has also added her own pieces to the puzzle. In June, as part of a broader economic plan, she proposed spending $2 trillion on green manufacturing, research and development, and the marketing of new technology overseas.

On Tuesday, Warren offered a fuller picture of her climate platform. Her goals -- which would be spurred by an additional $1 trillion -- include reaching zero-carbon emission commercial and residential for new buildings by 2028; zero-carbon emission on new light-duty passenger vehicles, medium-duty trucks and all buses by 2030; and zero-carbon emission and renewable electricity by 2035.

Kamala Harris

California Sen. Kamala Harris released a climate plan on Wednesday which aims for a carbon-neutral US economy by 2045, a more expedited timeline than others. The Democrat's plan touts $10 trillion in public and private spending, but the amount the federal government would spend was not released.

Harris' plan has many of the trademark Democratic climate proposals -- like reversing Trump's actions, investing in zero-emission transportation and carbon-neutral electricity and ending and federal subsidies for the fossil fuel industry -- but her plan also leans into the Climate Equity Act, legislation that she and Rep. Alexandria Ocasio-Cortez announced earlier this summer that focuses on "frontline communities," those that have experienced systemic socioeconomic disparities.

Harris' plan also harkens back to her time as a prosecutor, especially when she helped California win an $85 million settlement with Volkswagen for cheating on emissions tests for its diesel vehicles. If she becomes President, Harris' plan states, she will increase penalties for companies that violate federal pollution laws and restoring the "polluter pays" model for funding the Superfund program.

Cory Booker

New Jersey Sen. Cory Booker , too, uses a more expedited timeline in his climate proposal, aiming to spent $3 trillion to reach carbon neutrality by 2045.

Booker's plan, released on Tuesday, would put money in Americans pocked with a "progressive climate dividend" paid to Americans through new carbon fees placed on fossil fuel producers and would use executive action to undo much of Trump's climate action.

Unlike some candidates, Booker ties combating climate change with a direct focus on minority and vulnerable communities, arguing that those without significant economic means are more directly impacted by the issue.

"We are facing a dual crisis of climate change and economic inequality," Booker said in a statement. "Without immediate action, we risk an incredible human toll from disasters, health impacts, rising national security threats, and trillions of dollars in economic losses."

Julián Castro

Castro was another candidate who tied economic instability and vulnerable communities into his plan to combat climate change. Castro claims that his plan released on Tuesday would lead to $10 trillion in spending on addressing the climate crisis, but the former San Antonio mayor does not explicitly outline total federal spending.

But it is Castro's calls for an increased focus on how climate change most impacts vulnerable communities that set his plan apart. Castro says that within his first 100 days as president he will "propose new civil rights legislation to address the disparate impact of environmental discrimination and dismantle structures of environmental racism."

"The problem is that, like our neighborhoods, pollution is segregated," Castro writes in his proposal, noting a 2007 study that found more than half of the 9 million people living close to hazardous waste were black.

Pete Buttigieg

South Bend, Indiana, Mayor Pete Buttigieg takes a more technical approach to combating the climate crisis in his plan released on Wednesday.

Buttigieg explicitly outlines how the Department of Defense would take the lead in combating the issue by creating a "Climate Watch Floor" within the department. The plan also creates a new senior climate security role within the Pentagon.

In total, Buttigieg's plan would commit between $1.5 and 2 trillion to combat climate change, a number smaller than his opponents, but his campaign argued on Wednesday that these federal investments would leverage tens of trillions of dollars in private, state and local investments. Buttigieg's plan would also spend an additional $25 billion on climate research and make $5 billion annually available for grants aimed at rural America.

Buttigieg outright supports the Green New Deal and reentering the Paris climate agreement and would add $1 billion to the Low-Income Energy Assistance program, which helps cover bills in times of crisis like a heat wave or extreme cold.

Beto O'Rourke

Former Rep. Beto O'Rourke released earlier this year a plan focused on combatting climate change by spending $1.5 trillion to reform the United States' energy and transportation infrastructure. O'Roruke, who support portions, but not all, of the Green New Deal, says his plan would lead the United States to reach net-zero emissions by 2050 and leverage $5 trillion in investment.

Unlike other opponents, O'Rourke would like to work through Congress to set legally enforceable standards around pollution and emissions, a goal that, while more difficult, would make O'Rourke's proposal more lasting.

O'Rourke said around the release of his plan that a climate change proposal would be "very first bill he sends to Congress."

Amy Klobuchar

Minnesota Sen. Amy Klobuchar's plan, released days before the CNN town halls, would reinstate the clean power plant and gas mileage standard rules in her first 100 days as president, thereby repealing actions taken by Trump.

Klobuchar, in a more scaled back proposal and in line with O'Rourke, stresses the need to work through Congress to address the climate crisis, but says she will also "take aggressive executive action to confront" the issue.

Klobuchar's plan also seeks to get the United States to net-zero emissions by 2050, on track with many of her opponents. And like others, Klobuchar doesn't support all of the Green New Deal, but does back elements of the plan in her proposal. But the Minnesota Democrat does support reentering the Paris climate agreement.

Andrew Yang

Businessman Andrew Yang can lay claim to possibly the most unique climate plan in the field.

In his proposal released last week, Yang, an outsider candidate who has qualified for the Democratic debate later this month, has called the federal government to move people living in low-lying and flood prone areas to higher ground, seemingly conceding that rising sea levels cannot be reversed.

Yang also leans on his record as a tech entrepreneur and devotes significant portions of his plan for investment in new technology to combat the crisis, including expensive decarbonization research.