Residential energy use accounts for roughly 20% of all greenhouse gas emissions in the United States -- it's as much as countries like Brazil and Germany emit across their entire activity. What's more, these emissions show no signs of shrinking, despite some improvements in household energy efficiency.
A massive study that encompasses the energy demand and accompanying greenhouse gas emissions for 93 million American households shows there is still much room for improvement if the country is to meet its Paris Agreement climate targets for 2050 and beyond.
However, the burden is not shared equally -- quite far from it and rather unsurprising for a nation known for its rampant socioeconomic inequality. According to the study conducted by researchers at the University of Michigan, the homes of wealthy Americans generate about 25% more greenhouse gas emissions, on average, than those in lower-income neighborhoods. In the case of America's most affluent suburbs, emissions can be as much as 15 times higher than the poorest neighborhoods.
"The US is a huge country with an extremely varied housing stock. We had not seen a study of the greenhouse gas emissions (GHGs) from home energy use across the entire US (only for a few cities), even though these emissions are on the scale of Brazil's or Germany's. We stumbled across a large dataset with data on all US buildings and realized that there was an opportunity to do a truly comprehensive assessment of GHGs from household energy," lead author Benjamin Goldstein, a postdoctoral research fellow at University of Michigan's School for Environment and Sustainability, told ZME Science.
American mansions are ruining the climate for everyone
The CoreLogic dataset that Goldstein and colleagues accessed covers over 93 million homes in the contiguous United States, representing around 78% of the national total. The database consists of records of standardized tax assessors, which can be used to determine income, building attributes (age, heating fuel used, type of home), and energy consumption for households.
Greenhouse gas emissions per household were calculated as a function of square meters of residential floor space and the types of fuels used to generate electricity and heating for a given zip code.
Ultimately, these figures were centralized to paint an almost complete picture of America's household energy use and greenhouse gas emissions. This allowed the researchers to make projections about future energy use and greenhouse gas emissions for various scenarios of grid decarbonization and household energy efficiency improvements.
"The biggest challenge was running the scenarios to project emissions to 2050. We did this for about 60 million homes. For each home, each scenario, and for each year between 2015 and 2050 we had to keep track of household heating and cooling technologies, appliances, dynamic local heating and cooling demands under a changing climate, and decarbonizing electrical grids. That is about 8.4 billion household energy and GHG estimates over the entire model," Goldstein told me in an email.
The researchers' assessment shows that the residential GHG intensity is the lowest in the West, while the highest intensity was recorded in the central part of the country, where it can get much colder.
In fact, energy intensity requirements per square meter of floor space were unsurprisingly the lowest in warm and mild regions of the country, but much higher in cold north-central and northeastern states.
The most energy-intensive states were Maine, Vermont, and Wisconsin, while the least energy-intensive states were Florida, Arizona, and California.
A particularly representative city for the study's finding is Los Angeles.
"LA seems to be a tale of two cities. Wealthy areas - Beverly Hills, Hollywood Hills, Sherman Oaks - have very large homes and very high per capita emissions. Some of the lowest per capita emissions we observed across the country were in low-income areas not served by the LA Department of Water and Power, which has a carbon-intensive grid. Our national analysis found higher and lower emissions neighborhoods in other parts of the country, but LA seems to really encapsulate the extreme ends of the spectrum," Goldstein said.
"Wealthier households have high per capita GHG emissions from energy use than low-income households. This is largely driven by larger homes in wealthy neighborhoods," he added.
The study also makes a couple of remarkable observations, some of which can be interpreted as counter-intuitive.
For instance, energy-efficient households do not necessarily translate to low-carbon households. That's "since carbon-intensive electricity grids produce a lot of GHGs per unit delivered energy," according to Goldstein.
The spatial relationship between buildings also matters a lot. Taking Boston and Los Angeles as two different instances of residential density, the researchers found that "low-density, suburban neighborhoods generally had higher GHGs than dense, inner-city neighborhoods."
However, in both cities, the high-emissions neighborhoods were primarily high-income or extremely high-income locations. In contrast, more than half of the lowest-emissions neighborhoods in Boston and L.A. were occupied by people living below the poverty line.
Minimizing America's household carbon footprint
The researchers have identified two primary mitigation strategies for lowering greenhouse gas emissions tied to the U.S. residential sector.
The first approach obviously involves reducing fossil fuel use in both homes (i.e. gas burners for heating) and the grid (i.e. coal-fired power plants). This should be accompanied by home retrofits designed to cut energy use, as well as in-home fuel use if applicable.
Here's the thing, though: even if the entire U.S. grid is 100% decarbonized, meaning all fossil fuels have been phased out, that's still not enough to meet the 2050 Paris Agreement target of 80% emissions reduction.
Having a 100% renewable energy electricity grid would only reduce emissions from the residential housing sector by 28% -- enough to meet the 2025 target under the Paris Agreement, but anything more requires more aggressive home energy retrofits.
In most situations, this would mean transitioning towards smaller homes and denser settlement patterns. In other words, in order for the country to truly fulfill its most ambitious climate targets, most people would likely have to live in highly energy-efficient flats inside large apartment complexes, supplied by 100% clean energy for electricity, cooling, and heating. Of course, it's possible to build an ultra-low carbon footprint home in the suburbs, but that's currently prohibitively expensive for most Americans.
"There exists a number of mature technologies that homeowners can use to reduce their emissions. A lot of US homes are under-insulated and draughty. Installing insulation and new windows can greatly reduce energy bills. More expensive options include modern heating/cooling technologies and solar technologies. Heat pumps are an efficient way to heat and cool your homes, though the correct technology choice will depend on your climate (hot vs. cold). Geothermal heat pumps are especially effective systems that can reduce base energy demands. They also last for decades. Solar panels and solar water heaters substitutes fossil fuels, so these are effective ways to reduce emissions," Goldstein said.
"All of these technologies require financial investment. Although some Americans can afford to invest in low-carbon homes, there is room for the government to help low-income homeowners make these improvements using subsidies and tax breaks. Likewise, rental companies that do not foot the energy bill for the buildings they own also need similar incentives to make energy upgrades. Stringent energy regulations, such as though in the EU, have also been shown to be effective."
"It is important to note that individual households cannot solve this issue alone. The US needs coordinated action across scales and sectors to reach Paris. This includes decarbonization of the electrical grid alongside the necessary improvements to the housing stock," the researcher added.
In the future, the environmental sustainability lab at the University of Michigan is planning to explore and investigate other aspects of energy use and greenhouse gas emissions in the country.
"For instance, we have a PhD student working on the consumption of beef in California’s cities. Focusing on Costco, she reconstructed supply chains from the store back to the facilities that produce beef, finding that livestock production facilities contribute substantially to local air pollution in marginalized, rural communities in California’s Central Valley," Golstein said.
"Household emissions are particularly important because decisions made during building and renovating homes influence energy consumption and GHG emissions for decades. Given the severity of the climate change challenge, we need to make climate-conscious decisions today. Failing to do so risks contributing to further climate destabilization which will produce more extreme storms, sea-level rise, extreme heat, and other changes that will have negative impacts on our homes and our communities," he concluded.
The study appeared in the Proceedings of the National Academy of Sciences.