How do buildings contribute to climate change?

We know reducing carbon dioxide emissions is the only way to slow climate change. But what’s actually the biggest polluter? Judging from recent soundbites, it’s often hard to tell.

Global warming is caused by the combustion of fossil fuels, which leads to high levels of carbon dioxide—a greenhouse gas—accumulating in the atmosphere. During CNN’s Climate Change Forum earlier this month, Sen. Elizabeth Warren said: “I want to think about the three areas where we get the most carbon pollution in America right now. And what are they? They’re in our buildings and homes, right, what we’re burning. It’s our cars and light-duty trucks that we drive. And it’s the generation of electricity where we’re still using a lot of carbon-based fuel to make that happen.”

The CO2 emissions “pie” is more complicated than the sector-by-sector breakdown, as each of these areas contributes to the others. Understanding how exactly buildings contribute to carbon emissions is important for addressing the problem. And it turns out that buildings contribute to carbon emissions on multiple levels: in how we construct buildings, how we use them, and where they’re located.

What is the carbon footprint of a building?

Buildings and their construction together account for 36 percent of global energy use and 39 percent of energy-related carbon dioxide emissions annually, according to the United Nations Environment Program. In the United States, residential and commercial buildings account for 40 percent of energy consumption, according to the U.S. Energy Information Administration.

Building emissions, as typically measured, are a combination of two things. First is day-to-day energy use—known as the “operational carbon emissions” that comes from powering lighting, heating, and cooling. Globally, building operations account for about 28 percent of emissions annually. Second is the amount of carbon generated through manufacturing building materials, transporting materials to construction sites, and the actual construction process—what’s known as the “embodied carbon of a building,” which accounts for about one quarter of a building’s total lifecycle carbon emissions. Globally, the embodied carbon of a buildings account for about 11 percent of emissions.

How can the building sector reduce carbon emissions?

To meet the goals of the Paris Climate Agreement, which aims to limit global temperature rise to 1.5 degrees Celsius, the built environment’s energy intensity—a measure of how much energy buildings use—will have to improve by 30 percent by 2030, according to UN Environment. Globally, the energy intensity of the building sector is improving by about 1.5 percent every year; however, the number of buildings is on the rise—global floor area grows by about 2.3 percent annually—which offsets some of those energy intensity improvements. Carbon emissions related to buildings are expected to double by 2050 if action at scale doesn’t occur.

Decarbonization, or trying to eliminate carbon dioxide emissions, in the building industry can take many forms. This week, the World Resources Institute published a paper about ways the building sector and related policy at the local, regional, and federal levels can address emissions. “Although all buildings must be net zero carbon by 2050 to meet the goals of the Paris Agreement, not even 1 percent of buildings are considered net zero carbon today,” the report states.

Since most building-related carbon emissions come from energy use, the first—and easiest—step in addressing emissions is reducing consumption through energy efficient design. The next is replacing fossil fuels with on-site carbon-free renewable energy, then off-site renewables—a taller order since that means addressing our energy infrastructure. The final, and least preferred option, according to the WRI, is purchasing carbon offsets.

An energy efficient building could be a brand-new structure or an existing one retrofitted with new mechanical systems, heating, cooling, and lighting. In the United States about 95 percent of all buildings are more than a decade old and 82 percent of all commercial buildings were built before 2000. Meanwhile, about half of the floor space of all buildings in the U.S. is heated by burning fossil fuels onsite. Retrofits and renovations will be a crucial part of decarbonization.

Decarbonization could look like a net-zero building, meaning that it produces renewable energy onsite and delivers as much energy to the electric grid as it uses. Taking it one step further is a net-zero carbon building, meaning that it produces as much power as it consumes annually, and the power comes from carbon-free renewable energy sources onsite or nearby. A net-zero carbon building, including embodied carbon, means that the building produces enough renewable energy to meet operations annually and offset the carbon emitted from construction.

How is the building sector already reducing carbon emissions?

Leaders in the architecture and building industry are exploring ways they can make a difference—work that has been going on for many years through certification programs like LEED, Energy Star, Passive House, and the Living Building Challenge. But with the climate crisis coming into sharp relief, it’s taking on more urgency.

Architecture 2030, a group established in 2006, is working toward net-zero emissions in the building sector by 2050 by publishing educational materials and consulting with architects, policymakers, financial institutions, and governments. C40, a network of cities committed to addressing climate change, is pursuing net-zero carbon in all new buildings by 2030 and all buildings by 2050. Last year, the U.S. Green Building Council launched LEED Zero, a new program to help designers achieve zero net energy in their structures.

However, these effectiveness of these voluntary pledges is debatable. Of the 252 firms that have signed a 2030 pledge with the American Institute of Architects (AIA), the largest professional architecture organization in the U.S., only 16 have reached the benchmark goal of reducing energy consumption by 70 percent, compared to similar conventional buildings, in the projects they design. The average reduction from firms who signed the pledge is closer to 46 percent.

This week the AIA released a Climate Action Plan that shows how adapting architecture and design best practices can serve the 2050 goal. The AIA plans to hold more professional development courses on energy efficient design, increase initiatives to make low-carbon materials sourcing easier and more readily available, and lobby for building code updates—a critical measure to scale decarbonization.

How are cities reducing carbon emissions from their buildings?

Incremental approaches to decarbonizing buildings won’t be enough. What we need is policy at all levels of government: local, state, and federal. Cities like San Jose and Berkeley are banning gas hookups in new residential construction. New York City recently passed a slate of new bills in its Climate Mobilization Act, which calls for building retrofits to achieve a 40 percent decrease in greenhouse gas emissions by 2030. International cities are going even further. So far, 25 cities around the world have signed the C40 pledge to make all new buildings zero carbon.

But addressing building emissions isn’t just a matter of net-zero design. It’s really about how we live, how we work, and how we conceive of our environments—and the architecture, design, and construction industry will have to profoundly change. This is also where another slice of the CO2 pie comes into play: transportation, which accounts for about 29 percent of carbon emissions in the United States, according to the EPA. American land-use policy—the what and where of construction—is a major part of this problem. In other words, it’s car-dependent sprawl. Building denser, building close to transit, building more transit, and building amenities like on-site bike storage can help here.

The Architecture Lobby, a progressive organization of workers in the building industry, issued one of the strongest statements about how the building industry can respond to the climate crisis in its support of the Green New Deal. “Architects must embrace decarbonization as a social justice issue that calls for a reconstruction of our way of life,” it said. “We must redefine sustainability to acknowledge the economic, social, racial, and class-based dimensions of the climate crisis.”

If we’re to make a real difference with regard to climate change, it will involve an exciting transformation that’s bigger than buildings.