The most consequential impact of Trump’s climate policies? Wasted time.

For decades, climate experts have warned that delaying action to limit global warming would make the problem more dangerous and harder to solve. So how much impact did four years of delay under President Donald J. Trump actually have?On the total amount of extra carbon dioxide added to the atmosphere in the past few years, surprisingly little, says Leah Stokes, a climate policy expert at the University of California, Santa Barbara. But the bigger cost was to slow down progress that was being made. Climate and economic costs of creating a future with fewer fossil fuels are increasing steeply each year, so an extra four years on hold, at least in the United States, puts even more pressure on future leaders.“It’s not just that we’ve been moving in the wrong direction, but also we haven’t been moving in the right direction,” Stokes says.What policies mattered most?During his campaign in 2016, Trump had already announced his skepticism of climate change. After he took office in 2017, his administration made decision after decision that slowed or deprioritized climate action. It rolled back policies that helped mitigate warming, relaxed regulations for climate polluters, approved the Keystone XL pipeline, left the Paris Agreement, and more.In early 2017, for example, Trump told the EPA to dismantle the Clean Power Plan, an Obama-era policy that aimed to reduce carbon emissions from the power sector to 32 percent below 2005 levels by 2030. That plan would have avoided about 70 million tons of emissions by this year and over 400 million tons by 2030.