Democratic presidential candidates bet big on climate change at Tuesday night's debate, presenting it as a matter of life-or-death for the planet, and -- to judge by the frequency and passion with which they brought it up -- a winning general election issue. But few new details emerged about how each candidate would actually deal with the issue, even as they jostled fiercely for rank as the best choice for green voters.
Four of the five candidates at the Las Vegas forum -- most notably front-runner Hillary Clinton and her two most prominent competitors, Sen. Bernie Sanders of Vermont and former Gov. Martin O'Malley of Maryland -- highlighted the threat in their opening statements. But Sanders had perhaps the biggest moment, regaining some of his early edge as a climate hawk.
It came when the candidates were asked to rank the top threat facing the country. Former Secretary of State Clinton, former Rhode Island Gov. Lincoln Chafee and former Virginia Sen. Jim Webb ran through a familiar list of nuclear weapons, Iran, China and the spread of the Islamic State. O'Malley pulled from a similar list, mentioning that "climate change, of course, makes cascading threats even more dangerous."
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But Sanders singled out climate change alone when asked to name the "greatest national security threat."
"The scientific community is telling us that if we do not address the global crisis of climate change, transform our energy system away from fossil fuel to sustainable energy, the planet that we're going to be leaving our kids and our grandchildren may well not be habitable," he said. "That is a major crisis."
Clinton started the campaign to the right of Sanders on climate issues, or at least undeclared. But in recent weeks she has taken back some of his territory, coming out against the Keystone XL pipeline and drilling in the Arctic, two acid test issues for environmentalists.
On Tuesday she worked hard to portray these decisions as true to a long history of environmental action, including a central role in the 2009 Copenhagen Accords -- the first climate agreement signed by China.
That conference was a contentious near total failure, salvaged in the final hours when world leaders agreed on the goal of limiting warming to no more than 2 degrees Celsius.
"When we met in Copenhagen in 2009 and, literally, President Obama and I were hunting for the Chinese, going throughout this huge convention center, because we knew we had to get them to agree to something. Because there will be no effective efforts against climate change unless China and India join with the rest of the world," Clinton said.
"They told us they'd left for the airport," she continued. "We found out they were having a secret meeting. We marched up, we broke in, we said, "We've been looking all over for you. Let's sit down and talk about what we need to do. And we did come up with the first international agreement that China has signed."
Webb waved away that deal and Obama's more recent deals with the Chinese, arguing that they are non-binding and therefore "illusory," echoing a common Republican criticism. But Clinton and former O'Malley framed climate change in a slightly more business-friendly way than they have in the past, emphasizing the opportunity as much as the threat.
"We must square our shoulders to the great challenge of climate change and make this threat our opportunity. The future is what we make of it," O'Malley said.
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Clinton also deployed the "o"-word.
"I've traveled across our country over the last months, listening and learning, and I've put forward specific plans about how we're going to create more good-paying jobs: by investing in infrastructure and clean energy," Clinton said.
Her administration, she added, would seize "the opportunity posed by climate change to grow our economy."
Sanders made a similar claim in his opening statement, saying he would summon our "moral responsibility to transform our energy system away from fossil fuel to energy efficiency and sustainable energy and leave this planet a habitable planet for our children and our grandchildren."
But as for how each of them will actually do it, the debate offered few new revelations. Anna Bettis, a young viewer from Arizona, got the chance to ask for them.
"As a young person," she said, "I'm very concerned about climate change and how it will affect my future. As a presidential candidate, what will you do to address climate change?"
O'Malley touted his plan to move America onto a 100% clean electric grid by 2050, saying he would shift resources to it on his very first day in office.
No other candidate was given the chance to answer the question.