When we think of the culprits of climate change, we tend to picture coal-burning power plants, airplanes and traffic-clogged highways. But there are other offenders — the places we live, work, study and shop.
From urban high-rises to squat suburban malls, buildings are responsible for about 40% of global energy use and 30% of greenhouse gas emissions, according to the United Nations Environment Program. Officials say this amount could be significantly reduced by introducing relatively simple new practices and technologies.
Most of the average building's emissions come from everyday needs: to warm and cool our environment, provide light, cook food. And don't forget surfing the Internet.
The fossil fuels we rely on to generate this electricity create carbon dioxide emissions that trap heat in the atmosphere, resulting in a greenhouse effect. To achieve the goal of preventing global temperatures from rising more than 2 degrees Celsius — 3.6 degrees Fahrenheit — experts say improving buildings' energy efficiency is crucial.
With massive growth in new construction in developing economies, alongside inefficient existing structures in the developed world, the building sector offers much potential for long-term, cost-effective cuts in greenhouse gas emissions: Energy consumption in new and old buildings could be reduced by an estimated 30% to 80% by harnessing existing technologies, according to a 2009 U.N. report.
Part of the solution, environment advocates say, involves persuading consumers to change their habits, such as turning lights off when they leave a room and limiting their use of air conditioning.
Beyond that, tactics depend on where we live. In developed nations, the priority is retrofitting old buildings and making them more efficient: installing double-pane windows, insulating walls and roofs, upgrading to LED lighting.
In developing nations, the focus centers more on utilizing modern technology to design sophisticated new structures that introduce natural light and ventilation, as well as installing more renewable energy, such as rooftop solar panels and geothermal technology.
"Across the world, there are dual challenges," said Curt Garrigan, coordinator of the U.N. Environment Program's Sustainable Buildings and Climate Initiative. While projections show that most of the future building stock needed by 2050 is already in place in the developed world, more than half of the buildings needed in the developing world have yet to be built.
Historically, most emissions have come from North America, Europe and Central Asia, but emissions from developing countries are expected to make up the majority within a few decades.
With the global population expected to reach 8.5 billion by 2030, a major priority is urban residential buildings in emerging markets in China, Indonesia, Malaysia and North Africa, where people are expected to become more affluent and warm climates are projected to become even warmer.
"We're going to see an increased demand for air conditioning in a large part of the world," said Peter Graham, executive director of the Global Buildings Performance Network, a Paris-based policy group.
In many poor, rural parts of the world, a large amount of energy comes from burning wood, dung and crop residues to heat buildings and cook food. In China, one study found that energy use per capita was three times higher in rural than urban areas because of inefficient fuels, such as stalks and wood.
Yet experts warn that emissions are likely to increase as countries develop and consumers replace low-efficiency fuels — partly because electricity access prompts new demand for electrical devices. And electricity generated from fossil fuels is a key source of emissions.
Last week, as more than 190 nations met at the U.N. Climate Change Conference outside Paris in an effort to cut global warming, representatives of 20 countries and 60 organizations launched a new Global Alliance for Buildings and Construction to cut emissions levels in the building sector and build more climate resilience into urban infrastructure.
"We already have the technology, and we're already showing environmental and economic returns," Graham said. "The real challenge now is taking all this technology and know-how and trying to organize all of this capability to meet the 2-degree challenge."
Some parts of the globe are already setting ambitious new targets. France, for example, is working toward a "positive energy" program, requiring new, publicly subsidized buildings to produce more energy than they consume by 2020. China, the world's most rapidly developing country, is also introducing regional targets for improving energy efficiency in buildings.
In the United States, President Obama has sets targets for the federal government, which controls 360,000 buildings, to cut greenhouse gas emissions by 40% from 2008 levels by 2025. Some cities, such as New York, Boston and Denver, have also set goals to reduce greenhouse gas emissions by 80% by 2050.
In Philadelphia, where buildings account for up to 60% of the city's greenhouse emissions, researchers say the priority is making improvements to buildings in the commercial sector — such as hospitals, schools and grocery stores — rather than focusing on residential housing. Retrofitting large structures with high occupancies could cut buildings' energy consumption in half, said Patrick Gurian, an associate professor in Drexel University's College of Engineering and lead author of a study that explores how to limit carbon emissions in the city.
But raising the energy efficiency of buildings requires financial commitment. The Lima-Paris Action Agenda, a joint initiative of Peru, France and U.N. authorities, is calling for an additional $220 billion by 2020. Yet returns on investment, the group notes, could be as high as 124% if action is taken now.
The downside is that developers have to incur the initial cost for new structures that save over the long term. Many owners want their money back in a short time. "When you go to a hospital and you tell the manager you can save them energy, the utility bill is probably the last thing on their mind," Gurian said.
Ultimately, experts say, cutting emissions will require a host of new regulations and incentives. "The most effective policies involve mandatory building codes that require certain energy targets," Garrigan said.
Jarvie is a special correspondent.