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Calculations of climate effects from private luxury jets at Hanscom Field

Feb 10, 2024

There is considerable confusion about how the global warming effects of private jet travel are computed. This document explains the process. The global warming effects of emissions are the result of heat trapping effects known as "radiative forcing". Carbon dioxide is a well-known source of heat trapping and the result of fossil fuel combustion. However, for jet travel, there are other effects of contrails, ozone, soot, clouds, and other sources which add to the CO2 effect.

The global warming effect of jet emissions is expressed in carbon dioxide equivalent or CO2e, which includes both the CO2 contribution and the other effects resulting in radiative forcing. The contribution of CO2 is the direct result of burning fuel and is exactly 3.16 kg of CO2 for each kg of jet fuel burned. The other contributors to CO2e are the continuing subject of research, but various studies, including by the IPCC, have determined that the total radiative forcing multiplier is between 2 and 4 times that of CO2 alone. According to the ICAO, "Nearly two thirds of aviation's current effective radiative forcing is attributable to non-CO2 effects." Papers suggest a conservative multiplier of 2X to obtain CO2e from CO2 for high altitude jet aircraft.

Therefore, burning fuel at high altitude in a jet plane is about twice as bad for the climate  as would be expected from the carbon dioxide emissions alone.

The global warming contribution of jet flights can therefore be directly computed from the fuel consumption: 6.3 kg of CO2e for each kg of jet fuel. The contribution of a particular flight could be determined by measuring its fuel use, but this is not practical for a general analysis. Instead, there are generally available tables of fuel use for different aircraft, which describe how much fuel is consumed per hour. These tables are made based on averages across a flight, since fuel use varies during takeoff, cruising, and landing.

The fuel consumption of private jets ranges from 150 gallons per hour (very small Citation CJ3), to 540 gallons per hour (full size Gulfstream), depending on size and range of the airplane. The proponents consultants have suggested that Hanscom aircraft tend to be of the larger size. Private jets at Hanscom can be assumed to have a fuel consumption of 350 to 450 gallons per hour, which must be multiplied by 3.13 kg/gallon to get kg of fuel per hour.

The total annual flight time of a private jet ranges from 250 to 1200 hours. Therefore a single jet is responsible for between 1,700 and 8,300 tons of CO2e emissions per year.

The average flight duration from a specific airport could be found by tracking and averaging actual aircraft trips. For Hanscom Field, an average duration of 2.5 hours is a reasonable guess, although additional information could move this number up or down.¹ With this information, and considering the fuel consumption of 350-450 gal/hr, the CO2e of the a private jet fight from Hanscom Field is computed at 17-22 Tons of CO2e per flight, .

There are today 38,400 jet operations per year at Hanscom Field.² Half are arrivals, and half are departures. The airport enables both of these operations, so we can consider both in the calculations of the effects. The 38,400 operations can be directly calculated to result in between 660,000 and 850,000 tons of CO2e per year.

If doubling the airport hangar capacity only caused an increase of 50% in flights, the increase in CO2e would be between 330,000 and 425,000 tons, for a total of about 995,000 to 1,280,000 tons per year. Absent other information, this provides a reasonable projection of the expected impacts.

The number of 995,000 tons of CO2e, without context, has very little value in describing the magnitude of the impact. Here are some facts which put it in perspective:

A typical car emits 5 tons per year.

A typical 5kw residential solar array offsets 2 tons per year (Massachusetts)

The total installed solar PV in Concord is 11.2MW offsetting 4,400 tons per year ³

The total installed solar PV in Massachusetts is 4,100 MW offsetting 1,616,000 Tons per year. ³

The Town of Concord MA generates 180,000 Tons from all sources ⁴

These CO2e effects can be compared to the emissions of private jets. For example, a single typical private luxury jet each year creates 6,000 tones CO2e, as much as 1,200 typical cars. The current level emissions of private jets at Hanscom is cancels out the beneficial effects of betwen 41-53% of all the solar PV ever installed in Massachusetts. After the proposed project, Hanscom jet emissions could cancel out the beneficial effects of 62-79% of all the solar ever installed in Massachusetts.⁵ To make up for the emissions of luxury jets at Hanscom after this project would require :

Removing 180,000 fossil cars from the road

Adding 2,500 to 3,200 Megawatts of solar power.

Eliminating 100% of current emissions from about 5 municipalities near the airfield

Our communities are working hard to undertake significant climate-saving actions, which we had fully expected to reduce global warming. Unfortunately our actions will only go towards canceling a tiny amount of the greenhouse gas emissions of the private luxury jet traffic operating from within the surrounding towns.

It is alarming and discouraging that our climate efforts are canceled out by private aviation. As one commenter wrote: "How quaint that they drive their Tesla S to the runway—as if that makes up for the carbon output of flying directly from Hanscom to St. Bart or the Super Bowl (true examples)."

The emissions of private jets are colossally excessive when compared with the emissions of people outside of North America. A rural person in India is responsible for about 1 ton of CO2e per year. A single 36 hr round trip from Hanscom to India by an international Global 5000 private jet consuming about 510 Gal/hr results in 365 Tons CO2e. The amount of greenhouse gases generated by a single trip to India would therefore require a rural family of four in India nearly 100 years to produce.

The described emission values for Hanscom Field correspond to the impact including hangar expansion. Two thirds of this impact is already occurring. The new project to double the hangar capacity is conservatively estimated to be responsible for one third, but could result in much more. These estimates may be adjusted up or down if the airport releases additional information.

The potential for low-carbon aviation to mitigate these effects in the long term is currently only theoretical; it is discussed in this summary.

Note: these calculations have been revised over time to include nighttime operations for 2022,  to use a more conservative radiative forcing value of 2.0 instead of 2.2 , and change the assumed Massachusetts solar capacity factor from 14 to 15%.

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