Marin likes to pride itself on pioneering efforts to reduce its carbon footprint. But how well does the county actually reign in its emissions? 

A study released last month that took a unique approach to analyzing greenhouse gas emissions across nine counties in the Bay Area said Marin had the third-highest emissions per household, behind only Santa Clara and San Mateo. 

But the analysis also found significant discrepancies between towns and census tracts, and most West Marin coastal villages came in below the per-household average for Marin and the entire Bay Area. 

“It is a little unusual, because rural areas tend to have average or higher-than-average carbon footprints per household,” said Chris Jones, the program director of the CoolClimate Network at the University of California, Berkeley, and one of the authors of the study. “West Marin has some lower carbon footprints than you would expect.”

The study, titled “A Consumption-Based Greenhouse Gas Inventory of San Francisco Bay Area Neighborhoods, Cities and Counties: Prioritizing Climate Action for Different Location,” took an innovative approach to analyzing Bay Area emissions. 

Rather than using a traditional, territorial approach—that is, looking at where greenhouse gases are released into the atmosphere—the study by Mr. Jones and Daniel Kammen analyzed emissions from a consumption standpoint. 

For example, if an avocado is grown in southern California or Mexico but consumed by a person living in Bolinas, related emissions are assigned to Bolinas.

“It’s pretty rare, although increasingly common,” Mr. Jones said of the consumption-based method.

The researchers used some real consumption data, such as electricity and natural gas use, for the study. In other cases they took national surveys and pulled out Bay Area responses, or estimated consumption based on strong correlations, such as goods and services consumed related to household size and income.

Under this consumption-based model, Marin may have ranked higher in emissions compared to other Bay Area counties in part because Marin has higher average incomes. 

Yet income can only explain so much. For instance, Marin boasts lower per-household emissions than the United States generally, despite the fact that its average income is double the national average. Oakland has low per-household emissions even when controlled for income. 

The study found that the average household in the Bay Area produces 44.3 metric tons of greenhouse gases per year, whereas the national average is about 50. Marin County came in at 46.8. 

Almost all of Marin’s coastal census tracts came in below averages for Marin and the Bay Area. Point Reyes Station came in at 38.8 metric tons per household per year; Nicasio and Marshall at 38.14; northern Inverness at 41.2; southern Inverness and Inverness Park at 40.36; Bolinas at 41.03; Stinson at 38.58; and northern Lagunitas and Forest Knolls at 41.41. 

But the tract comprising the seashore and Olema was higher, at 47.15. The valley also had higher emissions than the county average: southern Lagunitas and Forest Knolls came in at 47.74; San Geronimo and much of Woodacre at 48.74; and another segment of Woodacre at 49.4. The largest discrepancies between coastal Marin and the valley appear to come from transportation emissions.

Eastern Marin has higher emissions. Larkspur and San Anselmo, for instance, came in at around 50 metric tons, portions of Mill Valley topped 60 and Ross had one of the highest per-household emissions, at about 70 metric tons.

Mr. Jones surmised that a combination of factors could contribute to West Marin’s lower outputs, including fewer demands on cooling than in communities further inland and the use of wood instead of natural gas to heat homes. 

He also said that culture could play a part. “I think if you ask people in West Marin, sustainability is really important. I think that their lifestyles reflect that, so we’re able to see that to some degree.”

Shannon Thompson, a three-year Point Reyes Station resident and a friend of Mr. Jones, was not surprised by the results. She cited resources like the online West Marin Commons, in which people give away goods or sell them secondhand, and the focus on consuming local foods as examples of how West Marin reduces its footprint. 

“People are sharing, exchanging and circulating goods instead of going over the hill,” she said. “And there are so many environmental groups. There’s a very heightened awareness…The most important thing is our collective impact. It’s not just jargon; it’s reality.”

Yet it also appears that income does account for some of the differences. The study used income data to estimate some aspects of consumption, and while Marin has an average income of roughly $140,000, that number varies by town. The average for Point Reyes Station is $103,000; for Bolinas, $98,000; for Inverness, $116,000. In Ross, one of the highest emitters, the average income is $215,000.  

Using consumption as the starting point significantly increases the amount of greenhouse gases that the Bay Area contributes to the atmosphere, compared to a territorial approach. Based on traditional measures, the nine counties contribute 86.6 million metric tons of greenhouses gases per year; based on consumption, they contribute 115.2 million metric tons—35 percent more. (To put that into perspective, the Environmental Protection Agency says that burning 103 gallons of gasoline produces about one metric ton of greenhouse
gasses.)

Much of that difference comes from food-related emissions, which contribute just over 1 million metric tons in a territorial approach, but 22 million metric tons when based on consumption. Electricity emissions are also much higher in a consumption approach; transportation emissions are roughly similar.

The biggest chunk of emissions in the Bay Area—a third—comes from transportation, including cars, public transport and air travel. Another 19 percent comes from food, 18 percent from goods, 18 percent for services and 13 for housing-related emissions. 

The study says that a consumption-based approach could help agencies and groups tailor emission reductions to specific communities.