Urbanization is widely recognized as one of the greatest threats to global biodiversity. But what about the biodiversity of cities themselves? As the world urbanizes, is the living world becoming more the same? The answer is surprisingly complex.

When snow in the Northeast finally melts away, so will the salt. But it doesn’t really leave. Road salt is part of a human-driven cycle that brings salt from places around the world into urban areas, where it remains even after it has washed out of sight.

It’s easy to vilify asphalt as the ultimate harbinger of the Anthropocene, the paver of paradise. But asphalt is also, more than just about any material, part of the intimate lived experience of most humans. Asphalt is the paver of paradise and our constant companion. How did it become the built world’s connective tissue?

Last April, I decided to take my students at Boston College out for a quick “forest bath.” Forest bathing is a trendy term for an old idea, which is that getting out in nature is helpful physically, mentally, and spiritually. And doing this exercise got me thinking: Is there an equivalent way to help people connect with the built environment? Is it possible to go “infrastructure bathing”? What would that even look like?

What do we lose by seeing ourselves as separate from nature? Let’s start with an example about carbon. Where are carbon dioxide sinks in urban areas? In this post, I’ll explore how dividing cities into “green” versus “gray” makes us overlook the complexity of how carbon cycles through the environment.