Monday, May 20, 2024

One of our few rooftop gardens in Cambridge – atop the Green Garage in Kendall Square. (Photo: Cambridge Mothers Out Front)

Let’s take a bird’s eye view of Cambridge. We see mostly empty rooftops, and some with mechanical systems on top to protect them from flood damage. Many of the flat roofs are heat-absorbing black, which can reach upwards of 140 degrees Fahrenheit in the summer, increasing the city’s heat island effects. These aren’t the rooftops that a city such as Cambridge, which is committed to fighting climate change, ought to have, and we know it. Why aren’t we acting on what we know? Why don’t we have more white roofs that can reduce surface temperatures by an average of 43 degrees in the summertime? More solar collectors? Where are roofs with growing plants? 

Scientific timetables tell us that Cambridge will experience a rising risk of flooding and longer periods of intense heat in the years ahead. Yet we’ve lost, not grown, our tree canopy. And we haven’t given enough consideration to roofs, a valuable resource for resilience in the face of circumstances we know are coming our way. It’s time to use these spaces wisely to protect against climate change while reducing our city’s heat islands and food deserts. We can do this, and we should.

Cambridge Mothers Out Front is launching a campaign to urge the city to do more than talk about green roofs and instead act to employ our city’s roof space in the fight against climate change. Rooftop gardens and farms insulate buildings, which decreases energy use and lower heating and cooling costs; and they prolong the life of the roof itself by blocking UV radiation that degrades roofing materials. Plants filter the air and cool the urban heat island as they photosynthesize, by absorbing carbon dioxide and releasing oxygen. Vegetated roofs help prevent flooding by capturing and slowing storm water discharge. Further, when solar collectors and green roofs are used in combination, they increase the efficiency of the panels by cooling the surface.

Green roofs can also serve another purpose in Cambridge: creating additional open spaces for residents. They can be parklike or active gardens for growing food. Think of our city’s successful community gardens, and imagine them on rooftops. Roof gardens are beautiful, and they can connect people to nature in neighborhoods throughout the city, which is something residents need and want. They provide habitat for pollinators, and help sustain biodiversity.

Clearly, green roofs are not meant to replace open spaces and trees on the ground, but to supplement and enrich the green infrastructure in Cambridge. We know from Cambridge’s own reports (a Climate Protection Plan in 2002; from the Cambridge Green Building Task Force in 2009; and this year’s Envision) that green infrastructure is crucial for mitigating climate change and for providing city dwellers with a high quality of life.

Mothers Out Front is a national environmental organization founded by two mothers sharing their concerns about the climate and their children’s future at a kitchen table in Cambridge in 2013. This volunteer-led organization is committed to halting and reversing climate change so that we ensure a livable climate for all children. Green roofs are a vital step. We urge city leadership to act more quickly, with zoning policies that call for green roofs on new construction and retrofits of buildings over a certain size and density. 

In neighboring Watertown, the city requires that buildings of a certain size put solar arrays on their roofs. In Cambridge, let’s do the same, and add green roofs to the strategies for those developing buildings in our city. Denver, San Francisco, New York City, Portland, Oregon and Toronto are leading the way on green roofs and solar arrays; and Boston has enviable urban farms on the Boston Medical Center and Fenway Park. When large buildings are built in our city – with large energy needs – residents ought to reap benefits that keep our city livable as climate change intensifies. We need to create green layers, on the ground and on our rooftops, if Cambridge is to remain livable for our children.


Florrie Wescoat is a member of Cambridge Mothers Out Front; Green Roofs Team members Leslie Bliss, Kathryn Rodgers, Melissa Ludtke, Wendy McCluskey and Diane Martin, contributed to this op-ed.