The politically expedient way to mitigate climate change is essentially no way at all, according to a comprehensive new study. Among the climate pollutants humans put into the atmosphere in significant quantities, the effects of carbon dioxide are the longest-lived, with effects on climate that extend thousands of years after emissions cease. But finding the political consensus to act on reducing carbon dioxide emissions has been nearly impossible. So there has been a movement to make up for that inaction by reducing emissions of other, shorter-lived gasses, such as methane, hydrofluorocarbons, and nitrous oxide, and particulates such as soot and black carbon, all of which contribute to warming as well.