Phasing out fossil fuels requires fundamentally changing our buildings

Opinion  Want to phase out fossil fuels? We must fundamentally change our buildings.

By Joseph G. Allen, 

Parichehr Salimifard and 

Jonathan Buonocore

September 26, 2022 at 7:00 a.m. EDT

Joseph G. Allen is an associate professor and director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health. Parichehr Salimifard is an assistant professor at the College of Engineering at Oregon State University. Jonathan Buonocore is an assistant professor at Boston University School of Public Health.

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Just about everybody understands that getting off fossil fuels is central to our climate goals. What few people understand, however, is that we won’t be able to do it without fundamentally changing our buildings.

Buildings consume an average of about 40 percent of U.S. energy. And in some cities, that number is much higher — upward of 70 percent.

Local governments are attempting to address this by passing legislation that would require building owners to reduce emissions from their energy use. Local Law 97 in New York City, for example, requires them to reduce greenhouse emissions by 40 percent by 2030 and by 80 percent by 2050. Those who don’t hit the target could face massive financial penalties.

These are worthy measures that will help to “electrify everything” — a strategy that will shift buildings away from dirty fossil fuels, such as natural gas, and toward the electrical grid. In the meantime, we can work to make the grid cleaner by expanding renewable energy, such as wind and solar.

The problem is, to make this work, we’re going to need a lot more renewable energy. One model from Princeton University shows that a plausible path to decarbonization would require 590,000 square kilometers dedicated to wind and solar power, which would be about the same size as Connecticut, Illinois, Indiana, Kentucky, Massachusetts, Ohio, Rhode Island and Tennessee combined.

Here’s another catch: Our energy needs vary dramatically by season. In summer, it’s dominated by electricity for air conditioning; in winter, it’s dominated by heating demand, mostly from gas. So phasing out fossil fuels would mean shifting when we put the most stress on the grid.

To help visualize the issue, we developed what we call the “falcon curve.” It shows that electrifying winter heating would reduce fossil fuel use, but this new extra electricity demand would be enough to shift the grid from summer peak to one that peaks in the winter. We call it the “falcon curve” because these new extreme peaks in December and January, when plotted out over the course of a year, look like the wingtips of a falcon. This is how it looks:

Without energy-efficient buildings, electricity demand will increase dramatically in the winter

The increase in demand would be nearly 30 times our current wind energy output or more than 300 times our solar energy output.

Electricity demand (Terawatt-hour)


Estimated increase in electricity demand if we replace fossil fuels with inefficient technology.


The “falcon curve”





Typical electricity use patterns in buildings today.








Sources: Jonathan J. Buonocore, Parichehr Salimifard, Zeyneb Magavi & Joseph G. Allen

(2022, Nature Scientific Reports).


Here’s why it’s such a big deal: If all buildings electrify their heating needs with the least efficient technologies on the market, we would need either 28 times more wind than we currently have or a staggering 303 times more solar to deal with the increase in electricity demands from using renewables.

But there are ways to flatten the falcon curve.

“Energy-efficient technology” might sound boring, but it is a powerful way for buildings to reduce energy needs especially during peak demand times. Healthy building tech, such as air quality sensors, can be used to deliver air only when and where it’s needed, rather than haphazardly dumping air into empty conference rooms. We can also use what’s called “energy recovery ventilation,” which simply means that after we spend all that energy to heat or cool a building, we don’t just exhaust it out of the building. That would be like heating your house in the winter and then leaving the windows open. Rather, the bad air goes out, but we first transfer that hot or cold air to the incoming air supply.

Meanwhile, climate tech, such as networked ground-source heat pumps, a technology being deployed in Massachusetts, can connect city neighborhoods to extremely energy-efficient geothermal energy. We can also develop and deploy long-term energy storage so that renewable energy captured at off-peak times can be used when demand spikes.

Altogether, efficient electrification can significantly reduce the need for renewable energy. Instead of having to multiply our current solar and wind power by 28 or 303, respectively, we find such technology would bring the need for solar and wind down to 4.5 or 36 times our current output. That’s much more achievable.

Transitioning away from fossil fuels would also come with a big bonus: improved health for humans. Our analysis published last year found that from 2008 to 2017, the number of deaths caused by burning coal dropped from about 60,000 per year to about 10,000 per year. Indeed, with coal receding as a source of energy, the dominant source of health damage from air pollution now comes from fossil fuel combustion in buildings.

These problems are interlinked. If we don’t get this right, we could very easily go down a path of inefficient electrification. That would force us to delay retiring fossil fuel power plants or to continue using fossil fuels in our buildings or other renewable energy sources, such as wood or biofuels, that might be carbon neutral but aren’t health neutral. That could jeopardize any ambitious decarbonization plan and all the resulting health benefits.

But we can — and must — take a different path. The technology we need is already available to us. We just need to use it.

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