Can cities really be ‰ÛÏgreen?‰Û They have to, if we are to build a sustainable society. The role of the ‰ÛÏbuilt environment‰Û is the theme of Earth Day 2014.

For many, the word ‰ÛÏenvironment‰Û conjures up some familiar and pleasing images: A dolphin launching itself above the ocean surface, perhaps, or herds of elk grazing in lush mountain meadows. Whatever the image, it’s probably accompanied by a soundtrack of whale songs or chirping birds.

Then there’s the human sphere ‰ÛÒ primarily cities ‰ÛÒ marked by traffic jams, bad air days, and the headache-inducing cacophony of car horns and jackhammers.

The phrase ‰ÛÏthe built environment‰Û is an oxymoron for most of us who are caught in this either-or mindset. But the truth is more complex. With half of humanity now living in cities (a percentage expected to rise to three-quarters by 2050), the built environment is our daily reality, and making cities green is a key to a sustainable future for the planet as a whole. That’s why the Earth Day Network (EDN) has made ‰ÛÏGreening our Cities‰Û the theme of this year’s Earth Day, the 44^th annual observance, on April 22.

According to the EDN: ‰ÛÏBy focusing onåÊbuildings, energy, and transportationåÊissues in cities this year, [we] hope to raise awareness about the importance of making improvements in efficiency, investments in renewable technology and regulation reform in the urban areas.‰Û

Transportation

How people get from point A to point B is a critically important part of the built environment. After all, vehicles account for a large share of primary energy usage and contribute huge quantities of greenhouse gas emissions. As science writer Elise Mulder Osenga points out in a separate article, cities like Hamburg, Germany, a 2011 European Green Capitol, have been transforming their transportation system to reduce their carbon footprint. Increasing the efficiency and availability of public transportation are important components to Hamburg’s ‰ÛÏgreening.‰Û The trend is also taking root in the United States, often considered the world’s most car-friendly industrialized nation. The numbers tell the story: With 2,605,000 paved miles of roads, the U.S. has the largest such network in the world. It also ranks near the top in miles of paved roads per capita (8,376) and is No. 1 in motor vehicles ownership (786 per 1,000). On average, Americans drive nearly 9,000 miles annually, with 86.1 percent of workers commuting in cars, trucks, or vans. The vast majority of the U.S. workforce (76.1 percent) drives to work alone.

But American car culture appears to be changing. Americans used public transportation 10.7 billion times in 2013, the highest ridership in 57 years, according to a recent report by the American Public Transportation Association. And the total distance driven has declined across several key metrics over the last few years, leading some analysts to conclude that the U.S. may have reached ‰ÛÏpeak car.‰Û

Public transportation isn’t the only alternative to our transportation problems, however. Another focus, in Hamburg and elsewhere, is making urban areas more friendly for bicycles.

‰ÛÏThe bicycle makes sense in cities,‰Û says Copenhagenize Design, a Danish consulting firm that advises cities on transportation issues. ‰ÛÏInvestment in bicycle infrastructure is a modern and intelligent move for a city to make.‰Û According to one study, society has a net profit of 23 cents for every kilometer traveled by bike, and a net loss of 16 cents for each kilometer covered by a car.

Copenhagenize Design took a novel approach to Earth observation to produce an analysis of how bikes and cars interact. For the project, ‰ÛÏThe Choreography of an Urban Intersection,‰Û the company first filmed a busy intersection outside of their office in Copenhagen for 12 hours on a typical Wednesday. Anthropologist Agnete Suhr then analyzed the footage for patterns and behaviors of both cyclists and operators of motorized vehicles. The result is an illuminating ‰ÛÒ and sometimes surprising ‰Û҉ÛÒ study of traffic that’s ‰ÛÏmore ballet than urban jungle warfare.‰Û

Bicycle sharing programs are popular in European cities like Hamburg, Paris, and Barcelona. After paying a one-time registration fee, urban residents rent bikes by the hour from stations located in high density areas. In the U.S., a country with a traditionally low number of commuters using bicycles, bike-sharing programs are spreading in urban areas including New York City, Boston, San Francisco, Denver, and Washington, D.C.

But more needs to be done to encourage bike usage, according to Jake Lynch, a spokesperson for the Rails-to-Trails Conservancy (RTC), a nonprofit based in Washington D.C.

‰ÛÏBike trails and pathways for active transportation are also proving themselves to be critical pieces in planning sustainable cities,‰Û he says. ‰ÛÏIncreasingly, people are choosing to live places where they are easily connected to shops, work and other destinations, where physical activity is a part of their everyday life, and where they have options for getting around. In a time when less and less Americans are choosing to get a driver’s license, biking and walking infrastructure is the key to attracting residents, reducing congestion, and building vibrant communities that function.”

RTC’s goal is to build a national network of bike and walking trails by re-purposing abandoned railway lines. When the group was founded in 1986, there were fewer than 200 ‰ÛÏrail-trails.‰Û Today, there are some 1,600 of these trails, spanning more than 20,000 miles and used by millions of Americans each year. Says Lynch, ‰ÛÏWalkable and bikeable communities are sustainable communities because they alleviate some of the massive environmental, social, logistical and health costs of a car-centric landscape.‰Û

Buildings

One-third of all greenhouse gas emissions worldwide come from the energy needs of buildings, but proper citing and design can dramatically reduce the environmental impacts of buildings, from carbon dioxide emissions to water use. On the 44th Earth Day, it’s instructive to look at the example set by Denis Hayes, the man who organized the very first Earth Day in 1970. Today, as president of the Seattle-based Bullitt Foundation, Hayes is working on several areas of sustainable development, including advances in green buildings.

‰ÛÏA deep green building is not a mere stylistic preference,‰Û says Hayes. It is, rather, ‰ÛÏa necessary component of resilient cities and resilient cities are a strategic necessity if the current generation is to pass on a diverse, habitable planet to the next.‰Û

The foundation is housed in the Bullitt Center, a six-story, 50,000-square-foot ‰ÛÏdeep green building‰Û that had its grand opening on Earth Day 2013. åÊThe building has a number of unique features, including pumps that draw heat from deep underground to warm the building and heat water, a rooftop solar array with 575 solar panels that produces more electricity than the building consumers in the summer, and an advanced waterless toilet system that composts waste without any odors.

Energy

The Bullitt Center represents a step down the road (or a pedal down the bike-path) to a green built environment, but it owes a large debt to an earlier ‰- and surprising— entry to the green building movement: the Reichstag. Located in Berlin, the German parliament building was rebuilt in 1999 to be a showcase for the country’s transition from a dependence on fossil-fuels and nuclear power to renewable energy.

The British architecture firm Foster + Partners replaced the heavy dome with a glass cupola housing a cone-shaped ‰”light sculpture.‰” Three hundred and sixty mirrors funnel natural sunlight down into the main parliament chamber, and solar panels power a metal curtain that tracks the sun’s path, filtering out the harshest rays. A cogenerator in the basement burns rapeseed oil to produce heat and electricity. In the summer, excess heat is pumped a thousand feet down into a natural aquifer, where it can be reclaimed to keep the Reichstag warm in the winter. When the building doesn’t produce enough electricity for all its needs, the government purchases power from exclusively renewable sources (primarily hydro, wind and solar).

While protecting wild areas will always be important, the organizers of Earth Day 2014 want people to understand that how we modify the built environment ‰- where most people now live ‰- plays a key role in creating a society that is sustainable for future generations.