The organizers of Power Shift say a green economy is the only way to head off catastrophic global warming and build a healthier future for everyone, including workers and their families. Pittsburgh was chosen for the biannual conference partly because it's at the crossroads of old and new energy. The city itself has banned fracking, yet the surrounding county recently signed a huge drilling lease for land under the Pittsburgh International Airport. Western Pennsylvania is also the birthplace of the oil and steel industries, but tech firms are attracted by students from Carnegie Mellon University and other schools.

Sierra Club executive director Michael Brune said their goal is to simultaneously decrease pollution from existing fossil fuels and increase clean energy, "while taking care of workers in the process."

"We have to begin replacing old, outdated, dirty fossil fuel projects with energy efficiency and clean energy," Brune said. "We're talking about a massive transition, with millions of people who will be affected."

The Power Shift conference is organized every two years by the Washington, D.C.-based Energy Action Coalition, with support this year from groups including the Sierra Club, the Natural Resources Defense Council, 350.org, and the Rockefeller Brothers Fund.

But it's not clear how much some of the members of Power Shift are willing to compromise with workers as far as the timing of shutting down polluting industries. On Saturday many Power Shift sponsors, such as 350.org, also held a "Global Frackdown" with protests that sought to "Ban Fracking Now."

Some young people attending Power Shift say they're sensitive to the needs of workers.

To change to a green economy "we need all hands on deck, and that includes the coal workers," said Seth Bush, a 23-year-old graduate of the University of Pittsburgh who now works for the Sierra Club. "And part of the conversation involves making sure that those people can put food on the table."

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