DENVER — After campaigning successfully last year as a “different kind of Republican,” Colorado Sen. Cory Gardner is under fire from conservationists for voting Wednesday against an amendment stating that humans contribute to climate change.

Fifteen Senate Republicans, including 2016 presidential contender Sen. Rand Paul, joined Democrats in backing the amendment, but not Gardner.

The vote took place amidst a flurry of amendments to the Republican bill to build the Keystone XL pipeline and were part of an effort by Senate Democrats to bait Republicans into a number of politically risky votes on the subject of climate change.

“We are surprised and disappointed that Senator Gardner chose not to join thirteen of his Republican colleagues in voting to agree that humans are having an impact on climate change,” said Conservation Colorado’s Pete Maysmith.

“This is an established fact in the scientific community.”

Gardner did join with almost every senator in voting yes on another amendment to the Keystone XL pipeline bill that states that “climate change is real and not a hoax,” which was approved on a 98-1 vote.

Most Republicans who voted that they believe humans contribute to global warming balked at another Democratic amendment stating that humans “significantly” contribute to climate change.

During a competitive U.S. Senate race last year, Gardner ran a TV ad shot in a wind farm touting himself as a next generation conservative who supports clean energy and an all of the above energy plan; however, during debates, he was reluctant to state a clear position on the role of humans in causing climate change.

“During this fall’s campaign, Senator Gardner declared himself to be a different kind of Republican,” Maysmith said. “Instead, his vote today shows that he is not yet ready to stand up to those in Washington DC who deny that people play a role in climate change.  He ducked this issue during the campaign and now on the floor of the U.S. Senate.

“We call on Senator Gardner to acknowledge and next time vote what a majority of Coloradans believe – that people are having an impact on climate change.”

According to a poll released following the November election, 69 percent of Coloradans want their senators to address the impact of climate change; the same poll showed that 68 percent of respondents are more likely to support a candidate “who accepts the scientific consensus that carbon pollution from man-made sources contributes to climate change.”

Gardner’s staff did not respond to FOX31 Denver’s request for a comment; this post will be updated if and when they do.

NOTE: An earlier version of this story mistakenly stated that the poll showed that 69 percent of Coloradans believe that humans are contributing to climate change. The author regrets the error.