These five speakers grapple with shifting notions of sustainability.

Judith Layzer advocates “strong sustainability” in lieu of the conventional approach, which imagines human-made capital and technology can always substitute for the wealth of resources drawn from the natural world. Development and affluence have instead degraded ecosystems. Strong sustainability “entails living within the productive capacity of nature…meeting the needs of the current generation as opposed to their demands.” Wealthy societies must adopt laws to contain population growth and curb consumption, and develop regional cooperation and fair trade policies.

Jason Corburn describes an environmental justice framework that connects ecological, economic and social justice issues, especially in urban settings. Corburn asks about the distribution of environmental goods and evils (such as parks and pollution); who participates in rule-making and enforcement; and how environmental justice evolves institutionally, and is enforced. The key lesson of the past is that voluntary enforcement of environmental justice guidelines don’t work, and we must “find a legal or regulatory stick to implement” its goals.

“Where I’m from, I see this green thing as a rich people’s movement,” says Phillip Thompson, who was a housing manager in New York. Environmentalists pushed clean air laws that ended the incineration of garbage -- but left housing projects with an unfunded mandate to bag their own waste. Thompson acknowledges the energy crisis is an emergency for many lower-income city dwellers hit with high heating costs: “We can’t do affordable housing if it isn’t green.” But transforming cities into affordable and green places means systemic change. Who, for example, will pay for outfitting buildings in poorer neighborhoods with energy conserving technology, and who will train and educate the workforce required for this transformation?

“What are we trying to sustain?” asks Chris Zegras. He believes the answer is access to opportunities that enable development. How do societies expand accessibility without depriving future generations of the ability to do so? Zegras says it’s hard to argue the importance of climate change to someone “who travels 3 ½ hours a day on a bus to get to a job, and half the salary is eaten up by the bus ride.” First, we must alleviate fundamental issues of accessibility for the poor: their lack of affordable transportation and proximity to schools and jobs. Zegras recommends addressing the worldwide crisis in transportation, in part through such innovations as bike and car sharing.

Looking down on Earth as if it were one country, says Adil Najam, you’d have to conclude it is poor, extremely divided, degraded, poorly governed and unsafe – a Third-world country. Addressing the environment turns on development, since “the poor are hit first and hit most.” The climate question has moved from discussion of molecules to adaptation, but we remain largely ignorant about how to mitigate and adapt, Najam says. Worse, nations are off on the wrong foot, measuring the problem in terms of only “emissions and dollars.” When a Bangladeshi fisherman loses his work to rising waters, what is the cost? “We need to add the currency of livelihood,” concludes Najam.