Cities in Climate Change Danger, Warns Capitan Planet

Cities: ground zero for climate change (Image: Flickr/Jamie in Bytown).

Cities have been getting a lot of love these days, as home to more than half of the world’s population and sites of revitalization, innovative governance strategies, and cultural vibrancy. But urban locations may also be ground zero for climate change, both as perpetrators of a warming atmosphere and as victims of its multi-tiered effects.

So says Dr. Shepherd Marshall, a professor of Geography and Atmospheric Sciences at the University of Georgia and a leading voice in climate science circles. “Cities are where things are most rapidly heating,” he says, “and they also represent particular concentrations of vulnerability.”

Localized heating in and around cities has long been noted – the “urban heat island effect” is caused largely by resurfacing vast areas with materials that absorb and trap short-wave radiation. Marshall and his colleagues, however, have noticed a new phenomenon in which the whole effect of agglomerated urban areas is greater than the sum of the parts. They’re calling it the urban heat archipelago, where “aggregate urban regions take on a disproportionately large climate forcing function,” Marshall says, “comparable to the scaling of a mountain chain versus an isolated mountain.”

The replacement effect is also significant. Paving over the Sahara Desert wouldn’t take too much primary production out of commission, but “we tend to put cities on the most fertile of landscapes,” as Marshall explains. After all, population centers typically formed around areas of consistent water availability – for food production or for trade purposes – and the spatial expansion of built areas removes highly productive land that would otherwise help sequester carbon.

The impacts of a warming climate will be felt disproportionately by cities, Marshall contends, because of growing population levels and dated infrastructure. The former creates more paved surfaces and more surface runoff, while the latter can’t always handle the new burden. “Stormwater management systems were designed for 1970s rainstorms,” Marshall says, but stronger storm events and decades of neglect have conspired to create a dangerous situation. On the other end of the spectrum, droughts can be more threatening to more people, since water storage capacity has not kept pace with growth. A medium-intensity 2007 drought in Atlanta, for example, caused a near-critical situation because more people were vying for the same quantity of reserves. At one point, the city was 30 days from running out of water.

Low-relief coastal cities – New Orleans, Houston, Miami, New York, Washington D.C. – are particularly vulnerable, as rising waters have cut the margin of error. “Hurricane Sandy wasn’t a particularly strong storm, all things considered,” Marshall says of the 2012 storm that wreaked havoc on the Eastern seaboard, “but it was pushing more water onshore than it would have 100 years ago.”

Marshall will be receiving the Captain Planet Protector of the Earth Award – yes, such an amazing title exists – today in Atlanta, in recognition of his hands-on environmental stewardship. And as a planetary guardian, he has some practical pointers that could help gird urban areas against the coming threats of a changing climate. “Strategic greening,” – it turns out placement and orientation matters when planting trees – “and having more white or highly reflective surfaces are things that can almost immediately reduce the temperature in cities.” It probably won’t be enough to save the planet on its own, but such minor modifications may at least help turn the tide.