Back in February the Washington Post ran a story about the number of natural gas leaks in DC. It’s an alarming read; there are a lot of leaks & many are potentially explosive. The natural gas utility was happy to refer us all to the existing plan to start fixing these, the cleverly capitalized PROJECTpipes. A big, and for the most part ignored, question is whether fixing this infrastructure is a reasonable thing to do. Why don’t we look at the impact of continued natural gas use and compare that with the costs & benefits of not burning it? I decided to start that analysis for my home.
Like almost all row houses in DC, mine is hooked up to natural gas. We use it to run our stove, hot water and the furnace for radiant heat. Of course this bugs me. I want to switch everything over to electric, but a lifetime of exposure to terrible electric cook-tops has kept this project deferred. However, I do value the environment more than my gas stove. So I downloaded my natural gas info from the utility here, Washington Gas, to figure out the impact of burning natural gas in my home.
After reading that story in the Post I want to understand how much leaked gas adds to the environmental impact of using gas in my home. According to the EPA the figure is 1.4%, but everyone seems to agree that the methodology behind that number is “deeply flawed”. The folks at the Global Energy Monitor did a study of US cities and found that DC's leak rate, accouting for everything from production to appliace loses, was 2.3%. A recent report from the DC Attorney General's office references a 6.2% figure, but I've been unable to find it's source. I'll stick with the 2.3% one, even though it's probably conservative.
Monthly therms used by billing month, May 2020 - April 2022. Retrieved from washingtongas.com
Natural gas is not a specific chemical compound. It’s a a mixture of gases that is at least 80% methane. It can also contain up to 10% ethane, no more than 5% propane and less than 2% butane. Other trace gases can also be present, but I’m gonna keep my calculations simple and ignore the non-methane content for now. Methane is bad enough.
The carbon footprint of burning natural gas is well known; 1 Therm produces ~11.7 lbs of CO2. The other half of the equation is the leaked gas, which again, is mostly methane. While an extremely potent green house gas, methane decays more rapidly than CO2. It has a half-life of 8.6 years once it’s in the atmosphere. This makes it difficult to compare to the more static presence of CO2.
Decay curve of methane's 8.6 year half-life & CO2's 50 year half-life
The two figures I’ve seen to describe this use different timescales;
- Over 20 years methane is 80 times as damaging as CO2
- Over 100 years methane is 25 times as damaging as CO2
Because the climate catastrophe is happening now, we’ll use the 20 year figure. For every therm I consume, I assume 0.023 therms have leaked out before getting to my home. Of that, 80% is methane, which is 80x as damaging as the same volume of CO2.
Monthly lbs CO2 equivalent emissions by month billed, May 2020 - April 2022.
The impact of using natural gas in my home is basically 50% worse than I’d previously assumed. The gas I don't even burn contributes significantly to the warming impact of using natural gas.
Burning natural gas I used in April 2021 generated 155 lbs of CO2. The leaked methane caused 80 lbs in CO2 equivalent emissions. A total footprint of 235 lbs for hot water and cooking a meal or two a day. As far as my natural gas use goes, this is a baseline. The months I need heat I burn, emit and leak much more.