Weekend Reads | Seattle's Greenhouse Gas Emissions

by Kevin Schofield

This weekend's read is a new report from the City of Seattle's Office of Sustainability and Environment, which provides an inventory of the city's greenhouse gas (GHG) emissions in 2020. It looks at both the magnitude of GHG emissions as well as the sources, and it gives us an interesting and insightful look at what it will take to make meaningful reduction in the city's contribution to global warming.

The report breaks out separately the city's "core" emissions — those that City policies can most directly impact — from the total "expanded" emissions that encompass all sectors and categories. As you can imagine, compiling all of this information is difficult. In some places, there is enough information to provide precise and highly accurate figures; for example, Seattle City Light and Puget Sound Energy have detailed data on electricity and natural gas consumption, broken out by residential, commercial, and industrial uses. However, other categories are rough estimates: Air transportation data (i.e., consumption of jet fuel) is low-certainty, and projections on road and rail transportation emissions are based on models — including estimates of how many of each type of vehicle are in use on Seattle's roads and the typical emissions of those vehicles.

The City's report compares emissions from 2008 to 2018, and then 2020. This is important context, because the COVID-19 pandemic changed everything: Businesses shut their offices and factories down, transportation came to a halt while we were in lockdown, and many people started working from home. At the same time, the city's population grew from 594,000 in 2008 to around 745,000 in 2018 (and then, according to the Census Bureau, shrank by about 10,000 people by 2020).

The city's overall greenhouse gas emissions — measured in "CO2 equivalent" to account for the differing warming impacts of various greenhouse gases — remained flat between 2008 and 2018 at about 6.3 million metric tons, though that represents a 21% drop in per-capita emissions given the population increase over that time. Then, in 2020, total emissions dropped by around 20% to 5.1 million metric tons, again largely due to the impact of the COVID-19 pandemic: Nearly all the reductions were in air and road transportation sectors.

So where do our city's greenhouse gas emissions come from? Of the roughly 5 million metric tons of C02-equivalent (CO2e) emitted in 2020, over half came from transportation, with passenger cars and air transportation making up the bulk; 58% of the emissions were related to gasoline, 29% was jet fuel, and 13% was diesel fuel.

Another quarter of the city's emissions is attributed to buildings: 15% commercial, and 10% residential. The biggest building contributor by far is burning natural gas, largely for heat.

Local industry contributes 18% of the city' emissions, split between energy use (building heat and running equipment) and "process" — i.e., chemical and combustion processes that emit greenhouse gases as part of the industry's production process. Cement processes create over a third of industry greenhouse gas emissions.

Perhaps surprisingly, waste collection and processing represent less than 2% of Seattle's greenhouse gas emissions.

It's interesting to see how much of a difference the pandemic made in 2020. Compared with 2018, transportation-related emissions dropped by 28%, mainly due to air, road, and rail reductions. Commercial buildings reduced emissions by 4.9% — and maybe we should be surprised that it wasn't more, given how many vacant buildings there were (and still are). Residential emissions dropped by 1.2%; and given that we all stayed home and kept the lights and heat on all day, perhaps we could have expected that to have even increased (in fact, residential natural gas emissions did go up slightly).

We don't yet know what has happened to greenhouse emissions post-2020. We could have a vigorous argument about whether we're "post-pandemic" yet, especially as it relates to employees returning to the office instead of working from home. That will affect road and rail transportation, as well as emissions from both commercial and residential buildings. We do know that air transportation has rebounded significantly this year, and we can expect that to be reflected in the post-2020 numbers.

The City's report also makes clear where the most impactful opportunities are for further greenhouse gas emissions reductions, the importance of which is very real given both the widespread droughts in the western United States and also the impacts to Seattle's air quality from wildfire smoke. The three big areas are road transportation, air transportation, and converting both commercial and residential buildings from gas to electric heat. Here in Seattle, we are fortunate that 90% of our local electricity comes from "clean" sources: mainly hydroelectric, but also wind and solar. That magnifies the impact that converting building heat from natural gas to electric and switching from gasoline-powered to electric cars can have. Over one-fifth of Seattle's greenhouse gas emissions come from burning natural gas, and one-third is from passenger automobiles. Both are ripe for switching to clean electricity.

2020 Community Greenhouse Gas Emissions Inventory

Featured image by Niccolo Bertoldi/Shutterstock.com.