In less than six years, Ed Mazria and his nonprofit group, Architecture 2030, based in Santa Fe, New Mexico, have leapt to the forefront of conversations about the role of buildings in global climate change. They got there simply by pointing out that the built environment has a disproportionate effect on the burning of fossil fuels.

Making the world’s new building stock carbon neutral within two decades is the challenge issued by Architecture 2030. In fact, Mazria has made it clear that seemingly minor design decisions, multiplied by tens of millions of buildings worldwide—from single-family homes to college dorms to high-rise office towers—can help reduce global energy use to a shocking extent. Reorienting a building in relation to the sun not only can trim home energy bills but can keep tons of carbon dioxide out of the atmosphere. After all, if a well-placed window means you don’t need air-conditioning, then your local power plant doesn’t have to burn coal to keep the juice flowing.

Here, Mazria explains what the climate-change debate all comes down to—–giving us some hints for what’s next in sustainable design.