The final debate between President Obama and challenger Mitt Romney on Monday night was a record breaker, and not just for the number of times someone said "tumult" or "bayonet." It also marked the first time in 24 years that an entire presidential debate season passed without a single mention of global warming.


Manmade climate change first came up in the 1988 debates, and was mentioned again during at least one general-election faceoff in 1992, 1996, 2000, 2004 and 2008 (see video below). Yet even though this summer brought record heat to the U.S., 2012 is now the first year since 1984 that no presidential or vice presidential candidate — or moderator — deemed global warming worthy of a national debate.


The theme of Monday's debate was foreign policy, so Obama and Romney mainly focused on issues related to defense, diplomacy and trade. They still had chances to address climate change, though, whose global nature inevitably makes it an international problem. (The U.S. military has recognized this, as did Secretary of State Hillary Clinton in a recent speech.) Moderator Bob Schieffer never asked about climate directly, but he at least opened the door with questions like "What do you believe is the greatest future threat to the national security of this country?"


While neither candidate mentioned global warming, both did talk about issues related to it. Obama was the first to bring up energy policy, citing his "all of the above" approach as a way to make the U.S. energy-independent.


"We've cut our oil imports to the lowest level in two decades because we've developed oil and natural gas," he said. "But we also have to develop clean energy technologies that will allow us to cut our exports in half by 2020." Romney later echoed this idea, pledging that "we are going to have North American energy independence. We're going to do it by taking full advantage of oil, coal, gas, nuclear and our renewables."


Obama and Romney often shifted to domestic issues despite the debate's theme, trying to frame foreign policy as a function of domestic strength. This revived some talking points from previous debates, including a brief spat over clean energy. "[I]f we're not making investments in education and basic research, which is not something that the private sector is doing at a sufficient pace right now and has never done, then we will lose the lead in things like clean energy technology," Obama said. Romney countered that "it's not government that makes business successful," repeating his earlier critiques of federal investment in clean energy companies.


Aside from that, the final debate of 2012 featured almost no debate on energy, let alone climate. The Obama campaign has tried to downplay this, recently emailing environmental groups with a list of climate references in Obama's stump speeches — including statements that it's "not a hoax" and is "one of the biggest issues of this generation." Yet Obama, Romney, Joe Biden and Paul Ryan all helped break the 20-year streak of climate change as a debate issue. And they may be snubbing more than environmentalists: A recent poll found 55 percent of all registered voters will consider candidates' views on global warming when deciding how to vote.


For a look back at environmental issues in past debates, check out this gallery of word clouds. And don't miss the video below, in which Brad Johnson of Climate Silence compiles two decades of climate debate (h/t Andy Revkin, Stephen Lacey):



For more environmental angles on U.S. politics leading up to Election Day on Nov. 6, see MNN's Politics page as well as the related stories below.


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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Obama-Romney debates end 20-year streak
For the first time in two decades, a U.S. presidential debate season has passed without any candidate or moderator mentioning climate change.