DON’T expect to hear much about climate change at the Republican and Democratic conventions.

Yes, there will be plenty of speeches about unemployment, budget deficits and other immediate problems. But the threats posed by global warming are decades away — or so we have been told repeatedly in recent years.

Many climate scientists, however, are now pointing to evidence linking rising global temperatures to the extreme weather we’re seeing around the planet. The United States has just endured its hottest 12-month period on record. The worst drought in a generation has parched the nation’s crop belt. Floods that happened once a century now occur every few years.

With distressing images of weather-related disasters saturating the news media, climate change no longer seems such a distant and abstract worry — except, perhaps, in Washington. In 2009, President Obama persuaded House Democrats, then in the majority, to pass a bill aimed at curbing greenhouse gas emissions. Facing a Republican filibuster in the Senate, however, the legislation died. And its prospects dimmed further when Republicans took control of the House in 2010. Mr. Obama has remained relatively silent on the issue since then.

Mitt Romney, for his part, has been equivocal about whether rising temperatures are caused by human action. But he has been adamant that uncertainty about climate change rules out policy intervention. “What I’m not willing to do,” he told an audience in New Hampshire last summer, “is spend trillions of dollars on something I don’t know the answer to.”