80% of the buildings that will be here in 2050 are already here, producing 30% of our greenhouse gas emissions. Uber sustainable new construction is cool, but the big carbon reductions will come from electrifying old buildings.

Chicago plans to retrofit 80,000 homes in the next 7 years. A research collaboration between the city, community organizations, a utility, and the National Renewable Energy Laboratory is working out a plan that will minimize emissions, maximize justice and lower peoples' energy bills.

The results convinced me that, at least in Chicago, it's far better to eliminate fossil fuel heating in lots of homes than to spend the same amount of money completely decarbonizing a lesser number. We need to do it all eventually, but this is the way to make big change fast.