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NASA's top climate scientist and government official James Hansen was arrested Wednesday outside the White House -- at least the fourth arrest now for the scientist.

Hansen, a controversial and highly vocal proponent of the argument that man's actions have dramatically affected the planet's climate, is the director of the Goddard Institute for Space Studies -- a position for which he earns a $180,000 taxpayer-paid salary.

'We have reached a fork in the road.' — James Hansen, head of the NASA Goddard Institute for Space Studies

He was arrested alongside actress Daryl Hannah; Adam Werbach, the founder of the Sierra Club; Bill McKibben, founder of 350.org; Julian Bond, former president of the NAACP; and a few dozen eco-activists protesting the planned Keystone XL oil pipeline from Canada to the U.S. Gulf of Mexico.

“We have reached a fork in the road," Hansen reportedly told a crowd of protesters before his arrest. "The politicians have to understand we either go down this road of exploiting every fossil fuel we have — tar sands, tar shale, off-shore drilling in the Arctic — but the science tells us we can’t do that without creating a situation ... our children and grandchildren will have no control over,” he said.

As a government employee, Hansen is essentially taking pot shots at his own employer. Yet a NASA spokesman told FoxNews.com after a 2011 arrest that what Hansen does in his own time is none of the government’s business.

"The agency doesn't comment on personnel matters," Ed Campion, a spokesman for parent organization Goddard Space Flight Center, told FoxNews.com.

“We really shouldn’t have to be put in handcuffs to stop KXL,” said 350.org founder Bill McKibben on Wednesday. “But given the amount of money on the other side, we’ve had to spend our bodies, and we’ll probably have to spend them again.”

In a May, 2012 essay for the New York Times, Hansen explained his decision to join the Tar Sands Action protest group, claiming that by burning the oil trapped in tar sand in Canada, the U.S. would be put dangerously at risk from climate change.

“The Western United States and the semi-arid region from North Dakota to Texas will develop semi-permanent drought … economic losses would be incalculable. More and more of the Midwest would be a dust bowl. California’s Central Valley could no longer be irrigated. Food prices would rise to unprecedented levels.”

Hansen has been arrested at least three times before in protests over climate issues, in 2009, 2010, and 2011.