A self-described conservative North Carolina businessman has promised to spend at least $5 million through his political action committee to back five Republican congressional candidates who have supported taking action to curb climate change.

Even as his party’s presumptive presidential nominee denies the existence of global warming, the businessman, Jay Faison, and his ClearPath Action Fund will spend at least $2 million on digital media campaigns to defend Senate incumbents running in two of the tightest races in the country, Rob Portman in Ohio and Kelly Ayotte in New Hampshire, a recognition of the senators’ support for clean energy, Mr. Faison said Wednesday. The advertisements are expected to start running this week.

ClearPath is also spending several hundred thousand dollars on digital advertising campaigns to support Representatives Carlos Curbelo of Florida and Tom Reed and Elise Stefanik of New York, all Republicans running for re-election in similarly tight races.