House lawmakers approved a Democratic amendment to a defense bill Wednesday that calls climate change a "direct threat to the national security" of the U.S. and orders up a Pentagon study, but only after some fiery opposition from Republicans.

Rep. Liz Cheney, R-Wyo., the daughter of former Vice President Dick Cheney, said she strongly opposed adding the measure to the National Defense Authorization Act during the House Armed Services markup session. The amendment was offered by Rep. Jim Langevin, D-R.I.

"There is no evidence that climate change causes war," Cheney said. "If you look at the refugee flows that are often cited, for example refugee flows across Syria and Iraq are greatest today, people are not leaving their home because they are too hot."

The amendment would require the military services to submit a study to Congress on the 10 facilities in each branch that are most susceptible to changing climate conditions and natural threats such as flooding, drought and wildfires.

The Armed Services Committee was building its final version of the NDAA, which must still be approved by the full House.

Some Republicans did back the amendment, saying it was a minor and reasonable step to order a study.

"There are real changes in the Arctic that do affect the Navy, the Acrtic ice is disappearing there are strategic changes that are being implicated here and it is important for the Department of Defense to report to Congress," said Rep. Jim Bridenstine, R-Okla. "We are talking about a report … It is just a report."

Democrats pressed that climate change is a legitimate threat to military operations and deserves a study.

Rep. Donald McEachin, D-Va., whose district borders Norfolk, Va., said rising seas are a fact of life and are threatening military bases at Hampton Roads.

"It is inconceivable to me that this committee would not want to understand this threat and take proactive steps to stop it," McEachin said.