e2 | PBS

Carbon trading is a business arrangement in which someone who produces CO2 pays a fee, which in turn is used to support a project that reduces CO2. The carbon trading market is a measurable and deliverable means to offset emissions for which a person is responsible. If all airline passengers paid a "carbon tax", for example, it could have a broad impact on carbon reduction projects around the world.

Portland is a city that successfully implemented a plan for transit-oriented development. Its urban planners made the public domain more appealing and accessible by emphasizing density and pedestrian travel. These transit policies are credited with spurring urban rejuvenation in Portland and many cities, while slowing the postwar dominance of the suburbs.

Cities are population magnets, and soon two thirds of the world's population will be urbanized. People often move to cities for economic opportunities, and this requires that the public domain be more than a place of automobile passage, but an interface for commerce and human interaction. Seoul is one of those cities, set apart by its focus on creating a positive public environment.

Today, food travels an average of 1,500 miles from its production source to plate. Now, however, the end of cheap, abundant fuel is leading to the end of cheap food. Unpredictable fossil fuel costs and federal ethanol policy are both reshaping the global food economy.

Paris' citywide bike-sharing plan, Velib', has been so successful that the mayor wants to create a similar system for cars. Autolib', as it would be called, could offer a reliable and affordable alternative to driving personal vehicles in the city's congested streets. Some, however, feel that giving people the option to use a car in lieu of public transport is a step backward.

The majority of the world's population is now urban, making cities major sources of greenhouse gas emissions. In response, leaders from 40 cities met in London to tackle the challenge of making urban areas less polluting. The result is a worldwide network of cities - named C40 - that shares innovative strategies and advances climate change policy on the political agenda.

The architects of 2012 Architecten in Rotterdam, The Netherlands, use discarded materials for their design purposes. But in order to work with waste, one needs certain tools. One of these is the "harvest map," a guide to regional dump sites and the materials they contain. Another tool is the Superuse Web site, where architects and the general public share designs that incorporate waste materials.

The Make It Right Foundation - founded by celebrity activist Brad Pitt - made history in storm-ravaged New Orleans by placing 150 pink symbolic homes in the city's hardest hit neighborhood, the Lower Ninth Ward. Each of Pitt's pink houses represents a sustainable home that will eventually be built in its place as money is raised by the foundation. Thirteen architects from around the world were recruited by Make It Right to design innovative, affordable, sustainable housing, which would also ensure the strongest protection possible against volatile weather.

The storm surge of Hurricane Katrina could have been mitigated had New Orleans' wetlands remained undeveloped. Now, citizens of the city's Lower Ninth Ward have begun the restoration of Bayou Bienvenue, which runs along the devastated neighborhood's northern border.

For architect Renzo Piano, the building site is a magical place where the art of construction takes place. He calls his office the Building Workshop, acknowledging the birthplace of his designs in respect to their final outcome: a structure. Ambivalent about tradition, he sees creation as a branch between past and future.

Melbourne, Australia's Council House 2, or CH2, has set a new standard for sustainable building design. While it employs established sustainable technologies, like energy and water conservation, the design includes many features that enhance the quality of the indoor environment.

Brian MacKay-Lyons feels that modern architecture education distances students from the tangible act of building. To provide students with more hands-on experience, he created the Ghost Architectural Laboratory. For two weeks each summer, students and professors work under MacKay-Lyons's guidance to build structures that explore what is sustainable and meaningful.

His Highness the Aga Khan, spiritual leader of the Ismaili Muslims, has deep ancestral roots in the city of Cairo. His sponsorship of numerous social and economic development projects is grounded in the principle that people should be active participants in their communities and cultures.

See architect and activist Edward Mazria's compelling presentation, which calls on buildings to be carbon neutral by the year 2030. Mazria has been speaking to leaders from the building industry and government on practical ways to reduce buildings' carbon footprint.

Dutch architect Frits van Dongen discusses his building, The Whale. The Whale is the centerpiece of Borneo Sporenburg, a high-density urban housing development situated on Amsterdam's eastern docklands. Van Dongen describes how many units in the building do not share the same floor plan.

Biophilia is a hypothesis that describes humans as emotionally connected to all other living systems. Jonathan Rose, a New York City-based real estate developer, describes how biophilia can guide building design in dense urban environments. In many instances, biophilia shares the same principles as sustainable building design.

During his tenure as mayor of Bogota, Colombia, Enrique Penalosa was both revered and scorned for his urban planning and transportation policies. His public works projects, which largely favored the pedestrian experience, were unlike anything previously built in Bogota. Penalosa describes the environmental and social importance of minimizing automobile culture.

Architect Thom Mayne describes his philosophy toward sustainability and design. Mayne, a Pritzker Prize-winner and the architect of the San Francisco Federal Building, is a maverick and a leader in his field. He believes that people will have to adapt to new, sustainable building designs now and into the future.

The Druk White Lotus School was constructed despite challenges ranging from financing, to Ladakh, India's harsh climate and remote location. The school's founder, His Holiness The Twelfth Gyalwang Drukpa, describes how the school was built in stages, while architect Jonathan Rose discusses the plethora of fundraising sources used for expansion.

A process called "carbon sequestration" may one day allow the United States and other countries to burn abundant coal reserves without emitting greenhouse gases. But the technology is far from complete, and some skeptics question its ability to effectively capture carbon dioxide. Learn more about the carbon capture process from leading researchers in the field.

Terry Tamminen, a policy advisor to California Governor Arnold Schwarzenegger on energy and environmental issues, helped draft much of the state's forward-thinking environmental policy. Tamminen discusses California's achievements, and the imperative of new laws and policies that promote sustainabile practices.

The production of ethanol and other biofuels requires many of the same resources - such as arable land - as the production of food. As the biofuel industry expands in the United States and abroad, there is increasing question of how food production will be impacted. Experts discuss the tension between these two industries in Brazil and the United States, the world's two largest ethanol producers.

Learn how ultra-lightweight materials are playing an increasingly crucial role in automobile design as manufacturers try to design more efficient vehicles. Jon Fox-Rubin, the president and C.E.O. of Fiberforge, demonstrates his company's production process for lightweight carbon fiber composites that will be used by the automotive industry.

Muhammad Yunus - the founder of the Grameen Bank and a Nobel Peace Prize-winner - describes his philosophy toward poverty, and how energy access can play a major role in poverty alleviation.

Learn how wind turbines are manufactured at the Suzlon Rotor Corporation in Pipestone, Minnesota, which supplies turbines to the state's rapidly expanding community-owned wind farms.

Meet maverick designer Cameron Sinclair, whose "design like you give a damn" credo was an inspiration for the e2 series.

Tad Fettig, the director of the e2 series, shares his perspectives on filming in China as this sleeping giant of industry, technology and consumer demand awakens in the 21st century.

A closer look at how much energy is used and how much pollution is created by construction. The impact on our environment is staggering.

Thirty years ago in Freiburg, Germany, the "Green Movement" was born. Today the city serves as a model of environmental consciousness for architects, planners, and even politicians.

Learn more about the inspirational architect Sergio Palleroni, who is introducing sustainability to poor and underdeveloped communities around the world.

David Owen, a writer for The New Yorker, discussues the complex issues of sustainability as they relate to urban and suburban life.