This weekend's read is a recent report from the City of Seattle that provides an inventory of our city's annual greenhouse gas emissions. It compares 2022 with previous years, most notably 2020 and 2008. It turns out that the year 2020 is a very interesting point of comparison, as it was the first year of the COVID-19 pandemic: People stopped traveling and started working from home, and tourism dramatically decreased — all of which can have dramatic effects on greenhouse gas emissions.
Early in the report, there is an important graph, showing the trends for emissions in the context of the city's population and gross domestic product (GDP) growth. The city's GDP, a measure of economic production, increased by 84% between 2008 and 2022, and the population grew 26% over the same years. Meanwhile, greenhouse gas emissions, both "core" (that the government has some measure of control over) and "expanded" (all emissions), decreased a bit — though the trend might have been slightly positive if not for COVID-19. But put together, it's a significant accomplishment that the economy and population grew while emissions did not; on a per-capita basis, our emissions dropped by about 26%.
As we dig into the details, we discover, as we might expect, that a few sectors contribute far more greenhouse gas emissions than others. Transportation accounts for 61% of all of the city's 2022 emissions, with air transportation 44% of that slice, and passenger road vehicles 42%. Buildings create one-quarter of the city's emissions, with the largest contributor being Puget Sound Energy's gas supplies, at 63% of the building emissions (split almost evenly between residential and commercial buildings). In comparison, industry only contributes about 16% of the emissions, and emissions from waste (such as methane from decomposing garbage) are a mere 1.6%.
In 2020, we did indeed see a big drop in emissions, especially for the transportation sector as people stopped flying and commuting to work. Two years later, emissions had partially rebounded to pre-COVID-19 levels, with air transportation leading the way — though Seattle's resistance to returning to the office means passenger vehicle emissions have taken longer to bounce back. Surprisingly, commercial building emissions didn't drop off much during COVID-19, and residential building emissions didn't increase much given how many people were working from home.
Building emissions in Seattle are very interesting; 55% of the energy consumed for buildings is electricity, but only 7% of building emissions are derived from electricity, because nearly all of the city's electricity production is "green" hydroelectric energy. As electric heat pump technology continues to roll out and replace gas heating systems, we can expect to see building emissions continue to drop — especially the gas contribution. This is particularly true for residential buildings, where the vast majority of emissions are fossil gas. For commercial buildings, where there is more equipment that runs on gasoline or diesel fuel (about 24% of total emissions), progress may be slower.
Greenhouse gas emissions from Seattle's industrial base saw a steep decline between 2008 and 2022, largely because of two sectors: cement and steel. Cement in particular reduced its emissions by more than half.
Emissions from waste have dropped 31% since 2008, due almost entirely to reductions by two sectors: commercial and construction/demolition. According to the city, this was not because of a reduction in waste generation, but because waste materials are being diverted and sorted for more appropriate handling that reduces greenhouse gas emissions. Meanwhile, residential waste emissions have held steady, though, as mentioned before, this is still a bit of a victory since the city's population has grown over that time.
The city's report accounts for two types of "negative emissions": carbon offsets purchased to counteract certain emissions; and carbon sequestration when organic waste materials are buried in landfills. Both have fluctuated since 2008, but offsets have been trending down over the long term — perhaps because commercial companies have been reducing the greenhouse emissions they needed to offset.
There are a couple of important takeaways from this report. First, the opportunities to make large reductions in the city's total greenhouse gas emissions will inevitably need to focus on the biggest contributors: air transportation, passenger vehicles, and gas for commercial and residential buildings. That doesn't mean we shouldn't look for other smaller opportunities — we can all do our part — but if the big emitters don't step up, smaller efforts might not move the needle appreciably.
Second, looking back, we can see that the COVID-19 pandemic was a very weird time. Air and road transportation emissions declined, and air transportation bounced back quickly, while road transportation has taken longer — though more recent data suggests that new back-to-the-office mandates are increasing road traffic. Yet, despite many people working from home, commercial and residential emissions haven't changed that much since pre-COVID-19 trends.
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