A rooftop is covered with solar panels at the Brooklyn Navy Yard in New York. (Mark Lennihan/AP)

Fewer Republicans say they believe that there is a scientific consensus on climate change or that the effects of global warming have already begun, according to a new Gallup poll, which showed a widening partisan gap near record levels.

The moves comes after a year in which President Trump, who has called global warming a “hoax,” withdrew from the 2015 Paris climate accord and removed climate change from a list of top national security threats.

As Republicans moved in one direction, Democrats have moved in the other. An increasing number of Democrats believe that the effects of global warming have already begun and that warming will pose a “serious threat” in their lifetimes. As in earlier surveys, an overwhelming portion of Democrats are worried about climate change and link it to human activities.

Overall, 45 percent of those surveyed said global warming would pose a serious threat in their lifetimes, the highest overall percentage recorded since Gallup first asked the question in 1997. Despite partisan divisions, majorities of Americans as a whole continue to believe by wide margins that most scientists think global warming is taking place, that it is caused by human activities and that its effects have begun.

But as it did last year, the Gallup poll painted sharp differences between the two parties. Nine out of 10 Democrats worry about global warming and believe it is caused by human activities. Only a third of Republicans do. Seven in 10 Republicans think the seriousness of global warming is “generally exaggerated,” while only 1 in 25 Democrats do.

Those positions inched further apart over the past year.

The divide between the parties grew most markedly on the question of whether the effects of global warming have already begun. Only 34 percent of Republicans agreed with that, down from 41 percent in early 2017. Meanwhile, 82 percent of Democrats agreed with that, up from 73 percent a year earlier.

Gallup asked whether people agreed that most scientists believe global warming is occurring, and 42 percent of Republicans said yes, down from 53 percent a year earlier and back to a level last seen in 2014. Just 35 percent of Republicans said that they believe global warming is caused by human activities, down from 40 percent.

Gallup surveyed 1,041 adults nationwide during the first week of March. The survey has a four-point margin of error overall but higher rates for each individual party.

Independents also became less convinced about climate change and its impacts. The portion of independents who believe global warming is caused by human behavior fell to 62 percent from 70 percent.