So far, the company has only released estimates for five cities, including Pittsburgh, Buenos Aires, and Mountain View, California. It plans to expand the program gradually to cover municipalities worldwide, but has declined to provide more specific plans. “What we envision is an open search bar for users to search for their own city in the future,” Van Groenou told me.

As part of this initiative, Google says it will also release its proprietary estimates of a city’s annual driving, biking, and transit ridership, generated from information collected by its popular mapping apps, Google Maps and Waze. The company has never released this kind of aggregate transportation data to the public before, and it says it may share even more specific types of data with individual local governments.

“This information has historically been really hard to get a hold of,” Van Groenou said. “But this is precise data, like looking at the ‘red-yellow-green’ traffic in Google Maps and aggregating it up for an entire year.”

Google made the announcement earlier this month as part of the Global Climate Action Summit in San Francisco. The summit, organized in part by California Governor Jerry Brown, was meant to encourage states and cities that have advanced climate policy since President Donald Trump took office. These local programs do much, but they have not replaced climate policies revoked by Trump: A recent report from Yale and a number of European think tanks found that these “subnational” programs could make up about half of the United States’ pledged carbon cuts under the Paris Agreement.

Google has framed the new project, called the Environmental Insights Explorer, as a way for leaders to focus and improve local climate programs.

The victims of climate change are already here.

The explorer remains a better tool for getting a glancing sense of a city’s carbon emissions than it is for making meticulous policy. Right now, it can only estimate carbon emissions from electricity and transportation—two important sources of pollution, but not the only ones. Heavy industry and agriculture, for instance, generate roughly a third of U.S. emissions. Google is also hampered by the age and quality of some data: To estimate how much carbon is emitted to power a given city, it must use a six-year-old data set from the EPA.

But it can still provide useful information. In Pittsburgh, for instance, it estimates that the power grid drives more than three times the emissions as the transportation sector. The situation is reversed in Buenos Aires, where cars and trucks produce twice the pollution created by the electricity grid.

“This is not sufficient information to decide whether to build another tunnel underneath the Hudson. We don’t know that yet. But we can say that in Buenos Aires, you should probably focus on transportation as opposed to building emissions,” Van Groenou said.