WASHINGTON — For the first time since the topic surfaced in a presidential race in 1988, nominees made no mention of climate change during the prime-time television debates this year between the presidential contenders themselves or their running mates.Debate moderators also chose not to ask President Barack Obama or former Massachusetts Gov. Mitt Romney about the issue, despite a clamor by climate activists and some not-so-gentle prodding on the part of pundits and scientists.

The national hush on climate change – which became a toxic political issue after a cap-and-trade bill collapsed in Congress in 2010 – became so deafening this election year that some activists dubbed it "climate silence." Some environmentalists struggled to summon enthusiasm for the Democratic president’s re-election campaign until Obama’s assertion that "climate change is not a hoax" brought delegates to their feet at the Democratic National Convention.

Even former Vice President Al Gore, whose film "An Inconvenient Truth" swayed public opinion on global warming, made mention of it during Monday night’s debate on foreign policy. "Where is global warming in this debate?" he asked on Twitter. "Climate change is an urgent foreign policy issue."

But no matter who takes office in January, the next administration will have to take bold steps to address global warming and its consequences, environmental experts say. Already, sea levels are rising in some places, and sea ice covering the Arctic Ocean fell to the lowest extent in satellite history this summer. Emergency managers have begun grappling with more intense hurricanes, drought and other extreme weather that could be tied to changing global temperatures.

In contrast to their lack of discussion on climate change, both candidates have talked extensively about developing domestic fossil fuel energy during the debates, with Obama disappointing some environmentalists by not turning his back on traditional sources of energy.

The question isn’t whether anything must be done on climate change after the election, said Andrew Steer, president of the World Resources Institute, an environmental think tank. The question instead is what must be done and whether it’s too late to adequately address global warming, he said.

"We are at the moment in a period in American history when, for various reasons, there’s been a confluence of factors that combined have led to this astonishing unwillingness to grapple with what clearly is a huge issue for the future for us all," Steer said. "I’m not confident that it will change. It’s a very serious and extremely discouraging situation right now."

The time spent on the issue may have been eclipsed by the economy and increasing gridlock in Washington. But in 2008, presidential candidates devoted 10 to 15 minutes to debating climate change, said Brad Johnson, who helped launch the "climate silence" activist website for Forecast the Facts and Friends of the Earth Action.

But there is one sign of progress for those tracking the issue. A Pew survey released last week found that the percentage of Americans saying that there’s solid evidence of global warming has steadily increased over the past several years.

Pew found that 67 percent of those polled believe there’s solid evidence the Earth’s average temperature has been getting warmer over the past few decades, said Leah Christian, a senior researcher for the Pew Research Center. That’s up 4 percentage points since Pew asked the question last year, and up 10 points since 2009, a low point for American attitudes toward global warming.

It remains unlikely, though, that Congress will have the bipartisan wherewithal to once again take on global warming. The Pew poll shows that Democrats are more likely to believe the Earth is warming. "We continue to see a wide partisan gap on this issue," Christian said. "The partisan gap hasn’t really shifted a whole lot."

That may be why much of the work to address climate change is happening outside of Washington, said Steer, who pointed to California’s plans in January to launch its own cap-and-trade program for large polluters and utilities. Reducing emissions doesn’t have to be a partisan issue or one of big government, he said. With a framework in place, he said, much of the work can be left to the private sector or state and local governments with creative ideas.

"In the meantime, we may need to rely on leadership elsewhere," Steer said.

And the election may prove a turning point, say environmentally minded political strategists. It can be a winning issue on the campaign trail, said Betsy Taylor, a political strategist who works with environmentalists. She teaches candidates and advocates to talk about putting American ingenuity to use to address global warming, rather than focusing on science. They also need to focus on the impacts of extreme weather, she said. In that context, people see climate change as their problem, not a faraway global one.

"It’s here," she said. "People believe it."