With the stroke of a pen, President Donald Trump signed an executive order last week that unwinds the environmental policies of his predecessor. The order directs the Environmental Protection Agency to begin withdrawing the Obama-era Clean Power Plan, which aimed to reduce carbon emissions by closing coal plants and building new solar and wind farms. By signing the order, Trump reiterated his campaign promise to bring back energy-industry jobs while bolstering arguments made by climate change opponents. But some experts think the act was more flash than substance, saying there is still a long and tangled regulatory path before America can abandon its role in curbing global warming.…