Cities Are Green After All

04/21/2015 02:23 pm ET | Updated Jun 21, 2015

Many of us are accustomed to think of urban smog as a root cause of global warming and environmental degradation that is pushing us to an existential precipice. Leading environmentalist Stewart Brand thinks otherwise. He explains why he was weaned from the village romanticism of a Mahatma Gandhi.

Agriculture Causes Global Warming
Drawing on the work of paleoclimatologist, William Ruddiman. Brand points out that the dozens of ice ages during the past 2.75 million years were largely explainable in terms of "three intersecting astronomical cycles affecting solar intensity. Ice-core data from Greenland matches the cyclic theory closely until about five thousand years ago, when, in the midst of our current routine interglacial, the standard steep drop in methane suddenly reversed and headed up."

Brand suggests that the cause was "the sudden adoption of irrigation in China and south Asia for an agricultural innovation, wet rice cultivation. Vegetation rotted in the new artificial wetlands and emitted methane."

A similar unexpected reversal in atmospheric carbon dioxide some eight thousand years ago is attributed to the burning of forests as agriculture took off, the population grew and forests were burned to make new fields thus turning the atmosphere into a greenhouse.

Just as agricultural activities are correlated with unusual global warming events, there are unusual drops in atmospheric carbon dioxide that mirror reduced farming. "What could explain the peculiar dips in atmospheric CO2 between 200 and 600, between 1300 and 1400, and 1500 and 1750? These dates happen to match major human diebacks from pandemics -- Roman era pandemics, the Black Death in Europe and the devastation of North American native populations by human diseases." So a case can be made that Stone Age farmers had a greater impact on the landscape per person than the average modern urban resident.

Why Cities are Greener than Villages
When we think of growing cities after the Industrial Revolution, the first thing most of us think about is smog, pollution and disease epidemics. How could cities possibly be green?

This argument rests partly on an analogy between body size in animals and town size. According to Kleiber's law (also known as the mouse to elephant curve) as animals get bigger, their metabolism slows down. hey become more energetically efficient. This is partly a matter of physics because larger animals have a smaller surface area to volume ratio which means that they lose heat more slowly. In cities, high rise building and the dense packing together of apartment homes means that less energy is used per person to heat homes. Bringing people together in cities increases efficiency because a little less of everything is needed per person, whether it is heating energy, electrical cable or water pipes.

Cities create environmental problems as they grow, of course, but they also generate innovations to solve those problems, such as catalytic converters to reduce air pollution, and vaccines to keep epidemic diseases in check.

One critical difference between bigger cities and bigger animals is that as animals get bigger, their bodies slow down so that a mouse has a much faster heartbeat (and lives a shorter life) compared to an elephant. As cities get bigger, they speed up because residents of larger cities are busier and more productive. They are also more creative, and they even walk faster. For these reasons, larger cities are hubs of economic growth and their business districts light up the night sky and glow from space.

Although they use lots of electricity, cities remain more efficient than villages in terms of energy use per person. Greenhouse gas emissions per person are consequently lower. Urbanites help the atmosphere further by avoiding the practice of agriculture. Who would have guessed that urbanization could be so good for the environment?