In the debate over how to respond to the perils posed by the earth’s changing climate, the ground has been rapidly shifting in recent years: as the Trump administration has retreated from efforts to curb greenhouse gas emissions and engage in climate diplomacy and public demand for action has grown—particularly among younger generations—cities and states have stepped into the breach.

Last Friday 16-year-old Swedish climate activist Greta Thunberg led the largest of her global climate strikes in advance of today’s United Nations Climate Action Summit, an attempt to spur countries and businesses to step up their efforts at reducing carbon emissions. These calls to action come just days after the Trump administration announced it would revoke California’s prerogative to set its own air pollution rules in a battle over vehicle-emissions standards. Though President Donald Trump plans to withdraw the U.S. from the landmark Paris climate agreement next year, dozens of cities and seven states, along with Washington, D.C., and Puerto Rico, have pledged to shift to 100 percent renewable energy to honor the agreement. The next few years will show whether this is a watershed moment.

During Gina McCarthy’s time as administrator of the Environmental Protection Agency under former president Barack Obama, she spearheaded many of the hallmark climate regulations that Trump is now undoing. Scientific American spoke with her about why she thinks we may be turning a corner on combatting climate change, the work she is doing in her new role as director of Harvard University’s Center for Climate, Health, and the Global Environment and what it has been like to watch as her signature accomplishments have been dismantled.

Are we, as a society, at a turning point in our willingness to combat climate change? And if so, what do you believe is fueling that shift?