DES MOINES — Setting ambitious goals for producing energy from the sun, wind and other renewable sources, Hillary Rodham Clinton seized on an issue Monday that increasingly resonates with Democratic voters and sets up a stark contrast with the Republican presidential field.

With many Republican candidates saying they do not believe that climate change is a threat or requires government intervention, Mrs. Clinton assailed their logic, saying, “The reality of climate change is unforgiving no matter what the deniers say.”

She set a goal to produce 33 percent of the nation’s electricity from renewable sources by 2027, up from 7 percent today — a higher goal than the 20 percent that President Obama has called for by 2030.

Mrs. Clinton’s strategists see climate change as a winning issue for 2016. They believe it is a cause she can advance to win over deep-pocketed donors and liberal activists in the nominating campaign, where she is facing Democratic challengers to her left on the issue. It is also one that can be a weapon against Republicans in a general election. Polls show that a majority of voters support candidates who pledge policy action on the warming climate.