Climate optimists argue that it is possible to reduce our production emissions without substantially changing our lifestyles. (Electric cars are just as good!) But what if those lifestyles — in which consumption is perpetually rising — are driving increases in production emissions elsewhere? What if they are making it more difficult for other countries, the ones producing the goods we consume, to reduce their emissions? Spoiler: They are.

If climate change really is a crisis, then surely we — especially the “we” in the wealthy developed world, doing most of the consuming — must take some responsibility for our consumption emissions. This is especially true if we want to make some room for the millions now living in grinding poverty around the world to reach something close to the lifestyles we now enjoy.

Fortunately, things are beginning to shift at the municipal level; cities are sharing to own up to the climate impacts of what they consume. Just a couple weeks ago, C40, a coalition of cities around the world committed to sustainability, issued a report on the “consumption-based GHG emissions of C40 cities.” It attempted, for the first time, to estimate the consumption emissions of 79 participating cities. This is no easy task.

While it’s comparatively easy to measure production emissions, consumptions are different. To directly measure them, a city would need to know about every single material good imported or purchased in the city and its exact lifecycle emissions. And because those things change constantly, a city would have to recalculate constantly. Still, we are finding accurate ways to estimate these numbers, and once we have them, cities can finally address the environmental impacts of their consumption. At the very least, it will be fascinating to see how the calculation of consumption-based emissions impacts the climate policy of cities in the future.