By Laila Kearney

(Reuters) - Seattle financial worker Harrison Karlewicz had been considering joining an environmental activist group for a while. The day after Donald Trump won the White House, he signed up.

"That was a big push for me, kind of a wakeup call," the 25-year-old said, after joining 350 Seattle, a group that stages mass protests against fossil fuel use. "I thought, 'I don't feel involved. I want to get out there.'"

During his campaign, Trump said global warming was a hoax and called for the Environmental Protection Agency to be gutted. He promised to "cancel" the Paris climate agreement between the United States and nearly 200 other countries to slow climate change, and he pledged to revive the coal industry.

Karlewicz represents what environmental activists say is the silver lining of Trump's electoral victory: Environmentally minded people angered by the outcome are rallying to their cause.

At 350 Seattle, people packed a volunteer drop-in meeting after news of Trump's confirmed win, said organizer Emily Johnston. The group blocked a rail line in Washington state that transports oil to Shell and Tesoro refineries earlier this year.

    "This was surprising to me, because I personally was so shaken that I felt practically paralyzed, and I know many other people did, too," Johnston said. "The fact that many others responded by immediately engaging is incredibly heartening."

Jay O'Hara, a Vermont-based climate-change activist with the Climate Disobedience Center and a mastermind behind a coal shipment blockade in 2013 that spurred more radical fossil fuel activism, said Trump's win represents an opportunity for environmentalists to focus on a clear enemy.

"In some ways, it can almost be seen as a relief,” he said of Trump's win. "We are going to have a real fight here, or maybe an actual argument."

Johnston, of 350 Seattle, who camped for a week at North Dakota's Standing Rock Sioux reservation to protest pipeline construction, said that protesters would continue to take advantage of the vulnerability of energy infrastructure.

"All these pipelines, all these tankers, all these trains have to go through thousands of miles" and could be potential protest targets, she said.

DEFENDING GAINS

Some of the well established national environmental organizations that helped draft the Obama administration's environmental initiatives, like the Clean Power Plan to curb carbon dioxide emissions, will be shifting to a defensive posture under Trump's leadership.

"We'll be in the Congress, in the courts, in the boardrooms and in the streets," said Gene Karpinski, president of the Washington-based League of Conservation Voters, which backed Trump's Democratic rival Hillary Clinton and spent over $45 million to support candidates in the 2016 elections.

Karpinski said he expected legal action to prevent Trump from following through on his agenda.

Trump has appointed Myron Ebell, a known climate skeptic, to guide the reshaping of the EPA, and Trump energy adviser Kevin Cramer, a U.S. representative from North Dakota, said Trump is likely to target the Clean Power Plan and Waters of the United States rules during his first 100 days in office.

Dan Farber, an environmental law professor at the University of California, Berkeley School of Law, said the best that advocates for climate change action could hope for from courts is to “play successful defense against an anti-environmental onslaught” from the new administration.

    “It’s a fairly grim situation,” he added.

Several groups also said they would put a greater focus on state-level environmental initiatives to sidestep Trump's administration.

The Sierra Club, which is headquartered in California, said it would push ahead with its Beyond Coal campaign, which has led to the retirement of hundreds of coal plants since it was launched more than a decade ago. The campaign mobilizes local activists and lawyers to push utilities and state regulators to shutter older plants and replace them with renewable energy.

"Clearly, we are going to have to fight and resist the worst impulses of the next administration," said Michael Brune, Sierra Club's executive director. "But we are also mindful that despite all odds, we were able to make great progress during the Bush administration and we hope to do it again."

(Reporting by Laila Kearned in New York; Additional reporting by Nia Williams, Nicole Mordant, Valerie Volcovici, and Lawrence Hurley; Editing by Simon Webb and Cynthia Osterman)