> ## Content Index > Fetch the complete content index at: https://airport.mmalc.com/llms.txt > Use this file to discover other available public pages before exploring further. # Growing air service at STS runs against Sonoma's climate goals - URL: https://airport.mmalc.com/sts-climate/ - Published: 2026-09-25T20:46:39.000Z - Updated: 2026-09-26T17:29:29.000Z - Description: Sonoma County's climate inventory counts the drive to Oakland but leaves out the flight from STS. Over the whole journey, growing local air service often means more aircraft movements, more emissions, and more travel. The lower-carbon alternative is the part the county can improve. - Author: Malcolm Crawford - Tags: pollution, climate change, airport Sonoma County's countywide climate goal is carbon neutrality by 2030, adopted in 2021 by the Regional Climate Protection Authority, the joint county-and-cities body that tracks it \[1\]. The Board of Supervisors' 2018 climate resolution sets out how transportation should cut its emissions, including reducing travel demand and shifting people toward low-carbon ways of getting around \[2\]. The county's latest greenhouse gas inventory, the scorecard for that goal, puts overall countywide emissions 22.7% below their 1990 level, but transportation 8.6% above it. It warns that carbon neutrality by 2030 is becoming increasingly improbable. Three of its accounting rules matter here \[3\]: - It deliberately leaves out air travel to and from local airports. - It doesn't count the flight from Charles M. Schulz–Sonoma County Airport (STS). - It does count a drive from Santa Rosa to Oakland's airport, at least the part inside the county. By that accounting, a traveler who flies from STS looks cleaner than one who drives to Oakland to fly. Over the whole trip, the opposite is usually true. Everyone flies either way. What changes is how many planes it takes to carry them. Where the same destinations are already served from Oakland, growing STS can split the same pool of travelers across additional flights, often on smaller regional aircraft. ## Road emissions are falling; STS passenger traffic roughly tripled Transportation is the county's biggest source of greenhouse gases, about 63% of the 2024 inventory \[3\]. Flights from STS appear nowhere in it. A rough estimate puts their carbon dioxide (CO₂) at about 60,000 tonnes a year, counting the whole of each departing flight \[4, 5\]. That's equivalent to about 2% of the county's latest inventory total, or about 3% of its transportation emissions, roughly what 13,000 typical cars emit in a year \[6\]. And the omitted activity has been growing. STS passengers roughly tripled between 2015 and 2025, while the county's on-road emissions fell about 12% \[3, 7, 8\]. Leaving air travel out of a community inventory isn't unusual, partly because most of a flight's emissions happen far from the county. But an inventory that leaves the flight out can't show whether airport growth helps the climate goal or hurts it. An earlier article on this site, [The local pollution cost of flying from Sonoma](https://airport.mmalc.com/sts-pollution/), found that an STS departure puts far more nitrogen oxides into Sonoma's air than the car journeys it replaces \[4\]. This article takes up the whole trip. ## Everyone flies either way, but not on the same number of planes For most Sonoma travelers, a new STS route doesn't decide whether they fly. It changes how they're carried. Suppose Sonoma's air travelers flew from Oakland instead. How many aircraft that takes depends on how the airlines respond, and there are two broad cases: - **The flights already running absorb them.** Nothing new takes off anywhere. Without those passengers to carry, the STS departure doesn't need to run, so there's one takeoff fewer in total. - **An airline adds a flight at Oakland.** A takeoff at Oakland replaces a takeoff at STS, usually on a larger aircraft carrying more people. The advantage doesn't come from Oakland being Oakland. It comes from carrying the same travelers on fewer or fuller planes. As of September 2026, every destination STS serves nonstop also has nonstop service from SFO or Oakland, and all but one from Oakland itself; Oakland's Dallas flights use Love Field rather than Dallas–Fort Worth \[9, 10, 11\]. So the choice isn't between a nonstop and a connection. It's between the same trip on different aircraft. ## Filling existing seats removes a takeoff instead of moving it A plane that's already flying burns only a little more fuel for each extra passenger. Taking a seat to Seattle on a Boeing 737-800 that's leaving Oakland anyway adds roughly 30 kilograms of CO₂ per passenger. The same passenger's share of a regional jet leaving STS with 60 people aboard is about 175 kilograms \[4, 5\]. Even after a 60-mile drive to Oakland in a gasoline car carrying 1.5 people on average, the Oakland trip comes to about 45 kilograms per passenger, against about 180 for the STS trip. To Los Angeles, the figures are about 35 and 145\. The notes give the calculations. Nitrogen oxides follow the same logic. The STS takeoff doesn't happen, so neither do its nitrogen oxides, in Sonoma or anywhere along its route. The extra weight on the Oakland flight adds only a small fraction of that. In this case consolidation wins outright, for both pollutants. The end point is not hypothetical. Sonoma's air travelers made about 780,000 journeys through STS in 2025, to destinations Oakland already serves. Oakland alone handled 10.8 million passengers in 2024, about 800,000 more than Oakland and STS carried between them in 2025 \[7, 12\]. Southwest alone serves every one of those destinations from Oakland except Dallas–Fort Worth, and it flies nothing but 737s: 803 aircraft seating 137 to 175, against an Embraer 175's 76 \[9, 10, 13\]. Whether airlines would carry that demand on flights already running or on flights they added is their decision, and it turns on how full the particular flights Sonoma travelers want already are, route by route and hour by hour. ## Growing STS can split the same passengers across more planes About three-quarters of STS passengers flew with regional airlines in the year to June 2026, mostly on jets like the 76-seat Embraer 175, and pilot contracts cap those regional jets at 76 seats \[4\]. A 737-800 has more than twice as many seats. Over a whole flight, the larger jet burns roughly 30% less fuel per seat \[5\]. Carrying 140 people to Portland on two Embraer 175s, one from STS and one from Oakland, instead of one 737-800 from Oakland means about a quarter more fuel and two takeoffs instead of one \[5\]. That's what growing STS can do where demand could instead be consolidated at a larger airport: divide one potential planeload between two aircraft. Larger jets at STS don't escape the problem. Southwest's 737s, which arrived at STS this year, fly to cities Southwest already serves from Oakland \[9, 10\]. Where the Oakland flights have empty seats, a Sonoma departure to Las Vegas is a second takeoff for travelers one plane could have carried. Even when an airline adds a 737-800 at Oakland to carry diverted Sonoma passengers, the whole trip usually comes out ahead on CO₂, provided the added flight fills up as typical flights do. To Seattle, with a shared gasoline car for the drive, it's about 140 kilograms per passenger against about 180 from STS. To Los Angeles, it's about 100 against about 145 \[5\]. Nitrogen oxides are different, and the difference matters. Near the ground, a 737-800 with the engines modeled in the earlier article emits nearly 40% more nitrogen oxides per passenger than an Embraer 175 on takeoff and climb \[4\]. So two regional jets can emit less nitrogen oxides around airports than one larger jet. Over a whole flight, most nitrogen oxides are emitted well above the airport, where they affect the climate and, spread thinly, air quality over a wide area rather than near the runway. There, two effects pull against each other. The larger jet burns about a third less fuel per passenger, but its engines emit nearly twice as much nitrogen oxide per kilogram of fuel at high thrust. No measurements of how much these engines emit at cruise power were found to settle which effect wins. Fuel is the difference that can be measured, and carbon dioxide is proportional to it. Carbon dioxide is also the long-lived, cumulative part of aviation's climate impact. Contrails last hours to days, and the atmospheric effects nitrogen oxides trigger play out over months to about a decade, while part of every tonne of carbon dioxide stays in the climate system for centuries \[14\]. So the case for fewer, larger planes rests on fuel and the number of takeoffs, not on nitrogen oxides. Oakland's neighbors count too, and the communities around the airport already carry heavy pollution burdens. Filling existing seats adds no flights there at all. Added flights would add some. For scale, all 780,637 STS passengers in 2025 would come to about 8.5% of Oakland's 9.2 million \[7, 12\]. Where consolidation does mean added flights, some takeoffs move to Oakland. The argument rests on removing aircraft movements where existing flights can absorb the passengers, and on carrying more people per movement where they can't, not on Oakland's neighbors counting for less. ## A few cases could favor STS, for now Oakland doesn't win every comparison. There are narrow cases where more STS flights could plausibly come out ahead: - **A full regional jet and a lone traveler's drive.** A full Embraer 175 from STS to Seattle comes to about 140 kilograms of CO₂ per passenger. If the Oakland option means an added flight and a lone traveler dropped off in a gasoline car that then drives home, it comes to about 165\. With a full regional jet and that kind of drive, STS comes out ahead on every route tested. With a shared car, STS only draws level, and only northbound: Oakland is about 60 miles south of STS, so flying to Seattle or Portland from there adds 9% to 11% to the flight distance \[5\]. - **Inbound visitors in gasoline rental cars.** The same arithmetic applies to visitors landing at Oakland and driving 60 to 70 miles to Sonoma. With a full regional jet into STS and one person per car, STS comes out slightly ahead from Seattle and about even from Los Angeles. - **Takeoff-and-climb nitrogen oxides, if Oakland adds larger jets.** For the reason above, an added 737-800 at Oakland emits nearly 40% more nitrogen oxides per passenger near the ground than a regional jet at STS. Those emissions land on Oakland's neighbors, not Sonoma's, and newer engines may change the comparison. Each case needs consolidation to fail, with airlines adding aircraft at Oakland instead of absorbing the passengers into flights already running. The first two need a gasoline drive as well. All three narrow if an STS route creates new travel rather than moving it. ## The drive is the part the climate plan can fix The drive to Oakland is the part of the comparison that can improve most quickly, and it's the part the climate plan works on. It's also what the cases above turn on, and every gasoline car replaced narrows them. The 2018 resolution's transportation goals include a shift to low-carbon options, more efficient vehicles, and low-carbon fuels \[2\]. For each passenger, the 60-mile drive produces about 14 kilograms of CO₂ in a gasoline car carrying 1.5 people on average. It's about 43 kilograms for a lone traveler dropped off by someone who then drives home. It's about 2 kilograms in an electric car, and about 1 kilogram on an electric coach carrying 30 people \[5\]. Groome Transportation already runs scheduled buses from Sonoma County to SFO and Oakland \[15\]. The aircraft side is much harder to decarbonize quickly. The regional jets flying from STS today will be the same types for years, and SkyWest, their largest operator, has ordered more of them \[4, 16\]. Every gain the plan makes on the road improves the 60-mile drive to Oakland far more than the short drive to STS. None of it touches the flight. ## New routes can create travel, while the plan aims to reduce it A new route can also create trips that wouldn't otherwise have happened. The air service industry calls this "stimulation," and it counts on it: studies of new routes find that traffic between two airports can jump well beyond its old level once a nonstop starts, with the biggest jumps on the smallest markets \[17, 18\]. Some of that growth is travelers switching from other airports, so it's an upper bound on new trips. But the emissions from any new trips a route creates have no avoided drive to set against them. None of them appear on the savings side of "it saves a drive." The county's 2018 resolution lists reducing travel demand as its first transportation goal \[2\]. That goal was written with land use and driving in mind, through more compact growth. A route built to generate travel pulls the other way. How much of STS's tripling is new travel, rather than travel moved from SFO and Oakland, isn't in any published county study found for this article. ## The alternative fits the climate plan's own goals Flying from STS is convenient, and that convenience is real. The problem isn't convenience itself. It's which option gets made convenient. Today, the convenient option is the one that tends to add takeoffs. A 2021 passenger leakage study presented to the county's Aviation Commission found that most air travel to and from the airport's catchment went through SFO or Oakland, and even after STS's growth since, most still does \[19, 20\]. Those travelers already fly from the larger airports. What residents among them don't have is an easy, clean way to get there. The 2018 resolution's goal of a shift toward low-carbon transportation options describes the kind of fix that's needed \[2\]. A satellite terminal on the US-101 corridor, with check-in, security, and baggage handled locally and a scheduled bus to Oakland, is one way to give residents that connection \[20, 21\]. It isn't a plan to move Sonoma's flights to Oakland. It's a way to connect Sonoma travelers to flights that already exist. Its likeliest first customers are people who already make the drive. The discussion paper proposing it takes no position on reducing STS service, and treats the system-wide emissions question as unresolved until it's modeled route by route. The figures here are a first step toward that modeling, not the final answer. The case for fewer flights is this article's own. The same travelers, on fewer and fuller planes, need fewer takeoffs. A route map that keeps growing at STS tends to do the opposite, adding aircraft movements and emissions the county's climate accounting doesn't count. *Claude (Anthropic) contributed to research and drafting.* --- ## Sources and calculation notes Sources checked September 25, 2026\. The calculations are illustrative itineraries and a rough annual estimate, not measurements of individual flights or a formal inventory. **Climate goals and inventory.** The countywide carbon-neutrality goal comes from the Sonoma Climate Mobilization Strategy, adopted by the Regional Climate Protection Authority (RCPA) board in 2021 \[1\]. It replaced the earlier target of 40% below 1990 levels by 2030, which the Board of Supervisors' Climate Change Action Resolution No. 18-0166 (May 8, 2018) committed to \[2\]. That resolution's transportation goals are to reduce travel demand through focused growth; encourage a shift toward low-carbon transportation options; increase vehicle and equipment fuel efficiency; encourage a shift toward low-carbon fuels; reduce idling; and switch equipment from fossil fuel to electricity \[2\]. The 2024 inventory update (August 2026) lists "emissions from air travel to or from local airports" among its intentional omissions. It reports 3,046,937 tonnes of CO₂-equivalent in 2024, 22.7% below the 1990 baseline of 3,944,000, and transportation at 1,922,683 tonnes (63.1%), 8.6% above 1990, of which on-road was 1,702,836 tonnes. It also states that prospects for countywide carbon neutrality by 2030 are increasingly improbable and that the goal may need to be reassessed \[3\]. A separate 2024 county plan targets carbon neutrality for county government operations, not countywide emissions, and isn't used here. **Scale of STS flight emissions.** Two rough methods, both counting the whole of each departing flight, gate to gate, the usual way of assigning flights to the airport they leave from. By departures: 6,320 scheduled departures in the 12 months to June 2026 \[4\], at 2,600 to 3,400 kg of fuel each (the ICAO range for an Embraer 175 on typical STS stage lengths, with larger jets higher) and 3.16 kg CO₂ per kg of fuel \[5\], gives 52,000 to 68,000 tonnes. Longer routes, such as Denver and Dallas–Fort Worth, and larger jets sit above that fuel range, so this method more likely understates than overstates. By passengers: 409,000 departing passengers in the same period \[4\], at 140 to 170 kg each (the per-passenger range in the itinerary table below), gives 57,000 to 70,000 tonnes. About 60,000 tonnes is equivalent to about 2.0% of the 2024 inventory total and 3.1% of its transportation emissions. The years differ, the inventory reports CO₂-equivalent while this estimate is CO₂ only, and the inventory measures emissions within the county while most flight emissions occur outside it, so the share is a sense of scale, not an accounting entry. A typical passenger vehicle emits about 4.6 tonnes of CO₂ a year \[6\]; 60,000 ÷ 4.6 ≈ 13,000\. Non-CO₂ effects of flying are excluded. **Growth comparison.** From the inventory's subsector series: on-road emissions fell 11.8% between 2015 and 2024, from 1,931,597 to 1,702,836 tonnes, leaving them 0.6% below 1990; off-road, which includes the airport's ground service equipment, rose 40.6% over the same period, from 154,696 to 217,577 tonnes; passenger rail has no 2015 figure, since SMART opened in 2017 \[3\]. STS passengers rose from about 263,000 in 2015 to 780,637 in 2025 \[7, 8\]. The flight-emissions estimate above scales with passengers, so treating it as a growth rate assumes emissions per passenger were unchanged; operations grew at a similar rate to passengers over the period, which is consistent with that, but it is an assumption rather than a measurement. On that basis the flights grew faster in percentage terms than any counted transport subsector over the same period, though off-road added more tonnes in absolute terms, about 63,000 against about 40,000. **Itinerary framing.** Each comparison carries one passenger one way from Santa Rosa. The STS option adds an Embraer 175 departure and a 7-mile drive to the airport. The Oakland options add a 60-mile road trip and either (a) an extra passenger on a 737-800 flight that would fly anyway, or (b) a share of a 737-800 flight an airline adds. Per-passenger flight emissions divide the flight's total by the assumed load: 60 passengers on the Embraer 175 (as in the earlier article) and 140 on the 737-800\. STS averaged 64.7 passengers per scheduled departure in the year to June 2026 \[4\]. The drive in each Oakland case is the kind of travel the county's inventory counts; the flights aren't. Inventories of this kind typically count road trips that begin or end in the county, at least in part; how the RCPA's method treats this particular trip wasn't checked. **Flight fuel.** Whole-flight fuel comes from ICAO's Carbon Emissions Calculator methodology, version 13.1, Appendix C: Embraer 175 (code E75) and Boeing 737-800 (code 738), interpolated linearly between the published distances of 250, 500, and 750 nautical miles \[5\]. Great-circle distances between airports get ICAO's routing allowance (50 km under 550 km, 100 km from 550 to 5,500 km). CO₂ is 3.16 kg per kg of fuel \[5\]. ICAO's table reflects typical operations, not any single airline's aircraft or flight. Seat comparisons use 76 seats for the Embraer 175 and 166 for the 737-800; configurations vary by airline. | Route | Great-circle miles from STS | from Oakland | Change | | ----------- | --------------------------- | ------------ | ------ | | Seattle | 618 | 672 | +8.7% | | Portland | 489 | 544 | +11.2% | | Las Vegas | 453 | 406 | −10.3% | | San Diego | 509 | 446 | −12.2% | | Los Angeles | 400 | 337 | −15.6% | **Extra passenger on an existing flight.** An aircraft's cruise fuel rises roughly in proportion to its weight. The estimate adds 100 kg for a passenger and bag to a 737-800 with a mid-flight mass of about 65 tonnes, plus 10% for carrying the extra fuel: about 0.17% of the flight's fuel. Applying that share to the whole flight, taxi included, slightly overstates it. That's an approximation, not an airline figure; doubling it wouldn't change any conclusion. **Road.** Gasoline: 8.887 kg CO₂ per gallon at 25 mpg, or 0.355 kg per vehicle-mile. Electric car: 0.30 kWh per mile at a California grid intensity of 0.198 kg CO₂ per kWh, or 0.059 kg per mile. Electric coach: 2.2 kWh per mile shared by 30 passengers. Airport bus (fuel unspecified): EPA's bus factor of 0.066 kg per passenger-mile. Bus and coach cases add a 2-mile shared car ride to the stop. Tailpipe and grid emissions only; manufacturing is excluded for every mode, aircraft included. **Per-passenger CO₂, one way from Santa Rosa (kg).** STS option: Embraer 175 with 60 aboard, plus the 7-mile drive. | Destination | STS | Oakland, existing seat, shared gasoline car | Oakland, added 737-800, shared gasoline car | Added 737-800, lone traveler dropped off by gasoline car | Added 737-800, electric car | | ----------- | --- | ------------------------------------------- | ------------------------------------------- | -------------------------------------------------------- | --------------------------- | | Seattle | 178 | 44 | 138 | 167 | 127 | | Portland | 156 | 40 | 122 | 151 | 111 | | Las Vegas | 151 | 37 | 109 | 138 | 97 | | San Diego | 158 | 38 | 113 | 141 | 101 | | Los Angeles | 144 | 35 | 100 | 129 | 88 | With a full Embraer 175 (76 aboard), the STS figures fall to 141 (Seattle), 123 (Portland), 119 (Las Vegas), 125 (San Diego), and 114 (Los Angeles). Against an added Oakland flight, a full regional jet from STS beats a lone traveler's gasoline drive with an empty return on every route, and roughly ties a shared gasoline car only to Seattle and Portland. **Inbound visitors.** A visitor from Seattle landing at Oakland and driving 65 miles alone in a gasoline rental car comes to about 147 kg, against about 139 kg on a full Embraer 175 into STS; at 1.5 people per car, about 140 against 139\. From Los Angeles, driving alone: about 109 against 112. **Two regional jets versus one larger jet.** From the same ICAO table: at 500 nautical miles, two Embraer 175s burn 5,978 kg against 4,621 kg for one 737-800 (+29%); at 300 and 750 nautical miles, +29% and +27%. Per seat at 500 nautical miles, 39.3 kg against 27.8 kg. One Embraer 175 from STS plus one from Oakland, against one 737-800 from Oakland: 6,018 kg against 4,792 kg to Portland (+26%), +25% to Seattle, and +32% to Las Vegas. On taxi, takeoff, and climb alone, using the earlier article's inputs, two Embraer 175s burn about 10% more fuel than one 737-800 (616 kg against 560 kg) \[4\]. **Southwest's fleet.** Southwest's own fact sheet records 803 Boeing 737s at the end of 2025 and no other type: 305 737-700s at 137 seats, 198 737-800s at 175, and 300 737-8s at 175 \[13\]. Its 737-800 configuration therefore seats more than the 166 assumed above, and its 737-700 fewer, which is why the comparison with the Embraer 175's 76 seats is given as a range rather than a multiple. Southwest's Oakland destinations were compared with STS's published route list \[9, 10\]; Southwest serves all of them from Oakland except Dallas–Fort Worth, where it serves Dallas Love Field instead. Southwest's share of Oakland's traffic is not used here. **Nitrogen oxides.** The earlier article's engine records give 3.03 kg of nitrogen oxides for an Embraer 175 departure (taxi, takeoff, and climb) and 9.80 kg for a 737-800, or about 51 g and 70 g per passenger at 60 and 140 aboard \[4\]. Those figures cover the airport area only. The databank reports emissions at takeoff, climb, approach, and idle thrust settings, not at cruise, and no cruise emission indices for these two engines were found, so the whole-trip nitrogen-oxide comparison can't be settled here. The available data do show why the direction can't be inferred from fuel burn alone. Per passenger, whole-trip nitrogen oxides are the product of fuel burned and the emission index in grams per kilogram of fuel. The 737-800 burns about a third less fuel per passenger, while the modeled engine's emission index is 1.98 times the Embraer 175's at takeoff thrust and 1.85 times at climb thrust \[4\]. Emission indices fall at the lower thrust used in cruise, and by how much for each engine is what's missing. A sensitivity calculation shows what turns on it: if the 1.85 ratio held at cruise, the 737-800 would emit about 25% more nitrogen oxides per passenger; at about 1.5 the two would be roughly equal; at 1.2 the 737-800 would emit about 20% less. Those are illustrative values, not measured bounds, and without cruise emission indices for the two engines there is no sound basis for choosing among them. At altitude, nitrogen oxides warm the climate mainly by forming ozone, partly offset by destroying methane. A widely cited assessment put aviation's net nitrogen-oxide warming in 2018 at about half that of its CO₂, and contrail cirrus above both, while attaching an uncertainty of about 70% to the contrail figure \[14\]. Later observational work complicates the contrail estimate further. Seven years of humidity measurements from instrumented airliners (June 2014 to December 2021) found that about 90% of northern-midlatitude conditions conducive to persistent contrails occurred where cirrus was already present. Fewer than 15% of all observed cases fell into the clear-sky or subvisible-cirrus conditions the authors associate with an unambiguous net-warming effect; most persistent-contrail conditions occurred within visible cirrus, where the incremental effect is smaller and uncertain in sign \[22\]. Those are global totals rather than route-level factors, so they aren't applied here. Carbon dioxide also differs from both in persisting for centuries: contrail effects dissipate over hours to days, while the atmospheric effects initiated by aviation's nitrogen oxides play out over months to roughly a decade. Nitrogen oxides (NOₓ) are not nitrous oxide (N₂O), a separate greenhouse gas. **Oakland.** 780,637 STS passengers in 2025 \[7\] against 9,210,509 at Oakland in 2025, down 14.7% from 10,803,382 in 2024 \[12\]. Both totals count arrivals and departures, so they are on the same basis. Oakland's 2025 total plus every STS passenger is 9,991,146, which is 812,236 below what Oakland handled in 2024\. That is an airport-level comparison: it shows Oakland has recently handled more traffic than it and STS carried together last year. It does not show spare seats on particular routes or departures, and airlines cut capacity as traffic fell, with passenger-carrier landed weight down 12.5% over the same period and total aircraft movements down 4.7% \[12\]. **Stimulation.** A study by SEO Amsterdam Economics estimated that a new direct route multiplies traffic between two airports, relative to the connecting traffic between them beforehand, by factors from about 9 for very small markets to about 1.3 for larger ones, and more for low-cost carriers \[17\]. Traffic on a new route includes passengers diverted from other airports, so these factors overstate new trips. No published STS forecast of stimulated demand was found; the airport's air service development work may contain one. ### Sources 1. Regional Climate Protection Authority, *RCPA Year in Review – 2021* (adoption of the Sonoma Climate Mobilization Strategy, countywide carbon neutrality by 2030). https://rcpa.ca.gov/rcpa-year-in-review-2021/ 2. Sonoma County Board of Supervisors, *Climate Change Action Resolution*, No. 18-0166, May 8, 2018\. https://permitsonoma.org/regulationsandlongrangeplans/longrangeplans/climatechangeactionresolution 3. Sonoma County Transportation and Climate Authorities, *Greenhouse Gas Inventory – 2024 Update*, final, August 10, 2026\. https://rcpa.ca.gov/wp-content/uploads/2026/08/GHG-Inventory-Update-2024-Full-Report-FINAL-2026-08-10.pdf — inventory page: https://rcpa.ca.gov/what-we-do/countywide-ghg-inventory/ 4. Sonoma Air Record, *The local pollution cost of flying from Sonoma* (engine inputs, BTS departures and passengers, fleet, scope clauses). https://airport.mmalc.com/sts-pollution/ 5. International Civil Aviation Organization, *ICAO Carbon Emissions Calculator Methodology*, version 13.1, August 2024, Appendix C and distance correction. https://icec.icao.int/Documents/Methodology%20ICAO%20Carbon%20Emissions%20Calculator\_v13\_Final.pdf — itinerary and annual arithmetic by the author, with road factors as listed in the notes. 6. U.S. Environmental Protection Agency, *Greenhouse Gas Emissions from a Typical Passenger Vehicle*. https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle 7. Charles M. Schulz–Sonoma County Airport, *Passenger Numbers*. https://sonomacountyairport.org/about-sts/passenger-numbers/ 8. Sonoma County Civil Grand Jury, *Sonoma County Airport: Addressing Challenges and Preparing for the Future*, 2025 (263,000 passengers in 2015). https://sonoma.courts.ca.gov/system/files/grand-jury/sonoma-county-airport.pdf 9. Charles M. Schulz–Sonoma County Airport, *Airline Information* (nonstop destinations). https://sonomacountyairport.org/passengers/airline-information/ 10. FlightConnections, *Flights from Oakland (OAK)*, checked September 25, 2026\. https://www.flightconnections.com/flights-from-oakland-east-bay-oak 11. FlightConnections, *Flights from San Francisco (SFO)*, checked September 25, 2026 (Dallas–Fort Worth nonstop). https://www.flightconnections.com/flights-from-san-francisco-sfo 12. Port of Oakland Finance Division, *Oakland San Francisco Bay Airport Monthly Activity Report, December 2025*(revised), calendar-year-to-date passenger totals. Report index: https://www.iflyoak.com/business/facts-figures/ 13. Southwest Airlines, *Corporate Fact Sheet*, information as of December 31, 2025 (fleet composition and seat counts). https://www.swamedia.com/pages/corporate-fact-sheet 14. Lee, D. S., et al., *The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018*, Atmospheric Environment 244, 117834, 2021\. https://doi.org/10.1016/j.atmosenv.2020.117834 15. Groome Transportation, *Sonoma County*. https://groometransportation.com/sonoma-county/ 16. SkyWest, Inc., *SkyWest Orders 60 New Embraer E175 Aircraft*, June 18, 2025\. https://www.businesswire.com/news/home/20250618426153/en/SkyWest-Orders-60-New-Embraer-E175-Aircraft 17. SEO Amsterdam Economics, *Market stimulation of new airline routes*. https://www.seo.nl/en/publications/market-stimulation-of-new-airline-routes-2/ 18. Abdelghany, A., and Guzhva, V. S., *Exploratory analysis of air travel demand stimulation in first-time served markets*, Journal of Air Transport Management 98, 2022\. https://ideas.repec.org/a/eee/jaitra/v98y2022ics0969699721001435.html 19. Sonoma County Aviation Commission, minutes of November 18, 2021, reporting the Crawford, Murphy & Tilly passenger leakage study. 20. *A satellite terminal in Sonoma County as an alternative to STS expansion* (discussion paper, August 2026), Sections 3.3 and 5.3–5.5\. https://airport.mmalc.com/satellite-terminal-discussion-paper-august-2026/ 21. Sonoma Air Record, *A discussion paper offers Sonoma County more air connectivity without a bigger airport*. https://airport.mmalc.com/satellite-terminal-discussion-paper/ 22. Petzold, A., et al., *Most long-lived contrails form within cirrus clouds with uncertain climate impact*, Nature Communications 16, 9695, November 3, 2025\. https://www.nature.com/articles/s41467-025-65532-2