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Conventional political wisdom says you don’t talk about climate change on the campaign trail.

That’s mostly because it’s a deeply polarizing issue. In a recent Pew Research Center survey, 72 percent of registered voters supporting Democrats in the upcoming midterm elections said climate change was a “very big” problem, compared with 11 percent of Republican voters.

That divide has led many candidates and the groups that support them, even those who favor addressing planet-warming emissions, to struggle with discussing the issue during election campaigns.

But that’s starting to change. Across the country, there’s been a small explosion of political ads about global warming.

In Nevada , the Democratic candidate for governor, Steve Sisolak, pledged in an ad to uphold the Paris Agreement. In Illinois, a Democratic candidate for the House, Sean Casten , assailed President Trump for calling climate change a “hoax.” And more than two dozen other candidates in tight races have released ads highlighting their views on climate change.