(CNN) CNN hosted a presidential town hall Wednesday night in New York City focused on the climate crisis. The event featured ten 2020 Democratic candidates, each of whom appeared on stage individually and took questions directly from a live studio audience — composed of Democratic voters interested in the issue — as well as CNN moderators.

We watched all seven hours. Here are the facts around some of their claims:

ExxonMobil

Sen. Kamala Harris, who formerly served as California's attorney general, was asked what she would do about "disinformation campaigns" from big businesses about the climate crisis. She advocated suing companies that have caused harm to people, just as "we did with the tobacco companies." Asked if that would mean suing ExxonMobil, Harris responded, "I have sued ExxonMobil."

Facts First: Though Harris has sued other big oil companies, she has not sued ExxonMobil.

When CNN asked what Harris was referring to, campaign press secretary Ian Sams emailed us a 2016 article about her decision as attorney general to begin an investigation into whether ExxonMobil lied to the public and shareholders about its knowledge of the risks posed by climate change.

But she did not file a lawsuit before she left the post to become a senator in 2017, and her successor as attorney general has also not done so.

As Sams noted, Harris did take legal action against oil companies on multiple occasions as attorney general. For example, after filing lawsuits , she secured a $14 million settlement from BP and Atlantic Richfield Company and a $11.5 million settlement with Phillips 66 and ConocoPhillips over allegations that they had violated laws governing underground fuel tanks.

Still, her claim at the town hall was that she sued ExxonMobil in particular, and it is false.

RL Miller, chair of the California Democratic Party's environmental caucus and president of the Climate Hawks Vote Super PAC, said on Twitter during the town hall: "As Cal AG, Harris opened a file shortly after the #ExxonKnew news broke in fall 2015. She never did anything with it."

The attorney general of New York filed a lawsuit against ExxonMobil in October 2018. Harris' successor, Xavier Becerra, declined to immediately join the lawsuit.

ExxonMobil denies any wrongdoing. The company says on its website : "#ExxonKnew is an orchestrated campaign that seeks to delegitimize ExxonMobil and misinterpret our climate change position and research. For the past several years, activist organizations have sought to punish ExxonMobil for voicing its opinion on climate policy, even though ExxonMobil supports policies to limit climate change."

Los Angeles

In discussing air pollution, Harris brought up the progress Los Angeles has made in cleaning up its air.

"Have any of you gone out to Los Angeles, California, about 20 years ago and remember what that sky looked like? It was brown. Babies had asthma. There were warnings that seniors should not go outside because breathing that ... would cause incredible damage to their lungs. And then leaders lead; the public said enough. You look up at the sky in Los Angeles today it's blue."

Facts First: The claim about Los Angeles's present-day skies is an exaggeration. Harris was correct that LA's skies are less polluted than they were 20 years ago, but it remains one of the The claim about Los Angeles's present-day skies is an exaggeration. Harris was correct that LA's skies are less polluted than they were 20 years ago, but it remains one of the most polluted cities in the country.

Air quality has improved in LA and in many cities around the country since the 1990s. This is largely due to better air quality-control policies at the federal, state and local levels. The improvement in air quality has had a positive health impact on LA residents. Studies show better lung function in children who live in the region.

Those bluer skies, though, are still extremely polluted . The Los Angeles area has the worst level of ozone pollution in the country, according to the annual American Lung Association's State of the Air report Ozone , also called smog, essentially causes a sunburn of the lung, irritating and inflaming the lining of our lungs when we breathe it in. It can leave us winded, cause asthma attacks , make us more susceptible to infection and even shorten our lives.

In 2018, the region violated federal smog standards 87 days in a row, the longest stretch in 20 years.

The Los Angeles area is fifth worst for year-round particle pollution and seventh for short-term particle pollution, according to the annual State of the Air report. Particle pollution is the mix of solid and liquid droplets in the air, according to the US Environmental Protection Agency. It can come in the form of dirt, dust, soot or smoke. Particle pollution comes from coal- and natural gas-fired plants, cars, agriculture, unpaved roads and construction sites.

California, while typically progressive on environmental issues, appears a disproportionate number of times on these bad air lists. It's in part because of topography that traps ozone and pollution. The sunny, warm climate doesn't help and neither do the pollution-generating activities of the 39 million people living there.

Cars, trucks, factories, oil and gas extraction, and power plants all create pollution.

Wildfires are also a big source of air pollution and are becoming a bigger problem with the climate crisis.

Green New Deal

During his town hall, businessman Andrew Yang claimed that the Green New Deal -- a Democratic resolution to address climate change -- called for banning air travel. "I love the vision of the Green New Deal," Yang said. "But the timeline they put out there would do away with commercial air travel and a lot of other things in a particular time frame."

Facts First: While an FAQ on the Green New Deal that circulated earlier this year did mention getting rid of emissions from air travel, the actual resolution does not.

New York Rep. Alexandria Ocasio-Cortez, who introduced the resolution in the House, had an FAQ released on her government webpage which explained that the resolution called for net-zero emissions in 10 years instead of zero emissions because "we aren't sure that we will be able to fully get rid of, for example, emissions from cows or air travel before then." The FAQ was not an official part of the GND and Democrats who supported the resolution did not endorse it.

The FAQ has since been removed. Ocasio-Cortez tweeted that "there are multiple doctored GND resolutions and FAQs floating around. There was also a draft version that got uploaded + taken down." She then pointed to the actual resolution which does not mandate that air travel be banned within a certain time period as Yang claimed. It does however call for "achieving net-zero greenhouse gas emissions" through "a 10-year national mobilization effort" as the summary of the bill notes.

Syria and climate change

Both South Bend, Indiana, Mayor Pete Buttigieg and former congressman Beto O'Rourke said climate change contributed to causing the Syrian civil war.

"Let's talk about national security, at a time when our military leaders say that this (climate change) is one of the greatest threats to stability. There's a lot of evidence that the Syrian civil war was one of the first that was partly caused as a consequence of climate change," Buttigieg said.

O'Rourke was more definitive, omitting the "partly."

"There will be a fierce competition for resources on this planet. Wars that were precipitated by climate change, like Syria, will pale in comparison to the wars that we see in the future," O'Rourke said.

Facts First: Buttigieg and O'Rourke did not invent this claim: scholars have published research arguing that climate change did contribute to creating the social conditions that led to the outbreak of the Syrian civil war. Other scholars, however, have argued that there is insufficient evidence for this conclusion.

The general argument from climate scientists who agree with Buttigieg and O'Rourke is this: Syria's major multi-year drought, which started in 2006 , was made more likely and more severe because of climate change; this drought caused poverty and hunger that led to significant internal migration from rural areas to cities; these issues fueled the social unrest that sparked the 2011 protests that led to the war.

In a paper published in 2015 in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), scholars from the University of California, Santa Barbara, and Columbia University noted that "civil unrest can never be said to have a simple or unique cause," and that Syria's was no exception.

But they wrote that "the drought had a catalytic effect" on unrest in Syria, and that the severity and duration of the drought were "more than twice as likely as a consequence of human interference in the climate system."

In a paper published in 2017 in the journal Political Geography, scholars on the other side, from the University of Sussex, University of Hamburg and elsewhere, wrote that "there is no clear and reliable evidence that anthropogenic climate change was a factor in Syria's pre-civil war drought; that this drought did not cause anywhere near the scale of migration that is often alleged; and that there exists no solid evidence that drought migration pressures in Syria contributed to civil war onset."

Regardless, it is clear that political factors unrelated to climate change, such as decades of repression from President Bashar al-Assad and his predecessor and late father Hafez al-Assad, contributed to producing the Syrian uprising.

Versions of Buttigieg and O'Rourke's claims have previously been made by President Barack Obama and Secretary of State John Kerry. Obama, unlike the two 2020 candidates, acknowledged that the research finding a link between the war and climate change was "not definitive." But he called it "powerful."

Yucca Mountain

While discussing the difficulty of storing nuclear waste, Harris claimed that the Trump administration put waste in Yucca Mountain, Nevada, in the middle of the night.

"They were, in the middle of the night -- this administration," Harris said, "in the middle of the night, carting in waste into Yucca mountain without the authority and the permission of the leaders of the state of Nevada."

Facts First: The Trump administration has not moved any nuclear waste to Nevada's Yucca Mountain, secretly or otherwise. In 2018, the federal government did move weapons-grade plutonium -- not waste -- to a different location, the Nevada National Security Site, without alerting the state's government.

The federal government has long had an eye on Yucca Mountain as a potential place to store nuclear waste; however, efforts have been continually held up. As the Yucca Mountain Information Office notes on its website, Yucca Mountain has no existing infrastructure to transport or store waste inside the mountain. "Today, the only thing that actually exists at Yucca Mountain is (a) single 5 mile exploratory tunnel," the website states

In 2017, a US district court in South Carolina ordered the federal government to remove at least 1 metric ton of plutonium from the Savannah River Site in South Carolina.

As a result, in 2018, the Energy Department moved half a metric ton of plutonium from the South Carolina site and onto the Nevada National Security Site, a federal nuclear laboratory. The move was made without alerting Nevada state authorities.

The State of Nevada filed a lawsuit in November 2018 to stop the potential transportation of the plutonium, but the Department of Energy -- in documents released in January as part of the lawsuit -- said that the plutonium had already been shipped. At the time, National Nuclear Security Administration (NNSA) Chief of Staff William White noted in a letter that the plutonium is not waste and will eventually "be used for vital national security missions."

In response to the revelation that the shipment had already been completed, US Sen. Catherine Cortez Masto of Nevada tweeted in January that "it's unconscionable that (the DOE and NNSA) failed to disclose the shipment of weapons grade plutonium to Nevada."

In their court filings , the DOE said that it does not "release information about the status of the shipment(s) until sometime after the shipping 'campaign' is concluded."

The Harris campaign declined to comment.

This story is being updated.