Air travel is currently our most convenient form of travel. However, the ability for planes to travel unimpeded over the United States, as well as over vast swaths of the globe, is governed by a complex set of national and international airspace laws. As the international community and individual countries have continued their efforts to combat the effects of climate change, reducing carbon emissions from air travel has come into increasing focus. This article reviews airspace rights, and then discusses the climate impacts of air travel to provide context to the challenges of decarbonizing the aviation sector. Various policy actions, use of “sustainable” biofuels, and the introduction of electric aircraft are currently options being implemented to reduce aviation carbon emissions. However, climate planning specifically addressing aviation emissions with a combination of decarbonization solutions, such as taxation of private jet travel and incentivizing modal shifts, will be necessary to achieve aviation sector climate goals.
Despite the constitutional right to travel from one state to another, there is no constitutional right to travel by flight. As the U.S. Supreme Court affirmed in 1969, the right to travel is a fundamental right under equal protection, where all are “free to travel throughout the length and breadth of our land uninhibited by statutes, [and] rules or regulations which unreasonably burden or restrict this movement.” Shapiro v. Thompson, 394 U.S. 618, 629 (1969). But 13 years later, the Fifth Circuit held in City of Houston v. FAA, 679 F.2d 1184, 1198 (5th Cir. 1982), that people do not enjoy “a constitutional right to the most convenient form of travel.” The Ninth Circuit aligned with the Fifth Circuit in 2006 with Gilmore v. Gonzales, holding that “the Constitution does not guarantee the right to travel by any particular form of transportation,” finding that the plaintiff did “not possess a fundamental right to travel by airplane even though it is the most convenient mode of travel for him.” 435 F.3d 1125, 1137 (9th Cir. 2006). Known as the “single mode doctrine,” the Second Circuit also took this position in the 2007 case Town of Southold v. Town of East Hampton, 477 F.3d 38, 54 (2d Cir. 2007), holding that “travelers do not have a constitutional right to the most convenient form of travel, and minor restrictions on travel simply do not amount to the denial of a fundamental right [to interstate travel].”
In 1940, Congress proclaimed that the “United States of America is hereby declared to possess and exercise complete and exclusive national sovereignty in the air space above the United States.” 49 U.S.C. § 176(a) (1940) (currently codified at 49 U.S.C. § 1508(a) (1976)). At common law, a landowner’s property right to airspace above their land was absolute—based upon the Latin phrase Cuius est solum, eius est usque ad coelum et ad inferos (“whoever’s is the soil, it is theirs all the way to Heaven and all the way to Hell”). Jackson Mun. Airport Auth. v. Evans, 191 So. 2d 126, 129 (Miss. 1966). Yet, after development of the airplane, Congress has also recognized that every U.S. citizen has “a public right of freedom of transit in air commerce through the navigable air space of the United States.” 49 U.S.C. § 1304 (1976).
The introduction of unmanned aircraft systems (UAS) complicated the lines between landowner property rights and the national airspace system. In 2005, the Federal Aviation Administration (FAA) issued its first airworthiness certificate for a civil unmanned aerial vehicle, and by 2013, the FAA had solicited proposals to create six unmanned aircraft systems, or drone test sites, throughout the United States to conduct the research needed to safely integrate such systems into the national airspace. In 2016, the first FAA-approved UAS package delivery to a house was made by Australian startup Flirtey. In 2018, the FAA issued a policy statement affirming its exclusive authority provided by Congress to regulate aviation safety and all aircraft operations—including UAS. Fed. Aviation Admin., FAA Statement—Federal vs. Local Drone Authority (July 20, 2018).
In 1919, the initial body of legal principles and rules between independent states—international air law—was first declared in Article 1 of the Convention Relating to the Regulation of Aerial Navigation: “The High Contracting Parties recognize that every Power has complete and exclusive sovereignty over the airspace above its territory. . . .” This rule was subsequently agreed upon in Chicago in 1944. See John Cobb Cooper, Roman Law and the Maxim “Cuius Est Solum” in International Air Law, 1 McGill L.J. 23 (1952). In 1944, the nine “freedoms of the air” were established and the International Civil Aviation Organization (ICAO) was formally created. As a United Nations (UN) agency, the ICAO has established environmental strategic objectives that align with UN sustainable development goals.
Air travel contributes a substantial share of global greenhouse gas (GHG) emissions. While the ICAO has an established carbon offsetting program intended to offset the growth of emissions due to air travel, it is insufficient to achieve global emissions reductions under the 2015 Paris Agreement. Air traffic worldwide is rapidly increasing annually, with an estimated daily global aviation consumption of 5 million barrels of oil and 3.16 kg of carbon dioxide (CO2) per kg of fuel burned in 2021. Farooq Sher et al., Unprecedented Impacts of Aviation Emissions on Global Environmental and Climate Change Scenario, 7 Current Pollution Reps. 549 (2021). Carbon dioxide is the highest carbon-based pollutant emitted from aircraft engines and represents 72% of total combustion chemical products. Id. The carbon footprint of the aviation sector is also increased after considering well-to-tank emissions for jet fuel (average of all emissions released into the atmosphere from production to delivery).
The aviation sector is difficult to decarbonize due to travel volumes and reliance on fossil-fueled commercial aircraft. U.S. airlines carried 194 million more passengers in 2022 as compared to 2021, and these figures are expected to continue to increase (though part of this growth is due to recovery from COVID-19). Because of projected growth within the aviation industry, in addition to other carbon emissions reduction solutions, modal shifts from commercial passenger flights, private flights, and cargo flights will be necessary to achieve state and federal climate goals.
In 2017, to regulate international aircraft emissions, the ICAO Council formally adopted an aircraft CO2 emissions standard, representing the world’s first carbon emissions standard for any sector. This standard was applicable to new aircraft designs from 2020 and to aircraft designs already in production as of 2023; those in production by 2028 that do not meet the standard will no longer be able to be produced unless the designs are sufficiently modified. However, no other current carbon emissions standard is in effect globally that applies to most commercial aircraft.
The other international regulatory action taken to curb aviation emissions is implementation of CORSIA, the Carbon Offsetting and Reduction Scheme for International Aviation. CORSIA is the first international, market-based measure to stabilize carbon emissions from international aviation. Under CORSIA, airlines will be required to monitor emissions on all international routes and then subsequently offset their emissions from routes included in the scheme through purchase of eligible emission units generated by projects that reduce emissions in other sectors (such as renewable energy). While 126 countries voluntarily participate in this program, carbon offset programs such as CORSIA aren’t intended to replace efforts to reduce carbon emissions within the aviation sector (and it does not directly encourage airlines to reduce emissions through advances in aircraft technology, operations, and infrastructure).
On the U.S. side, the U.S. Environmental Protection Agency (EPA) has worked with the ICAO since 2010 on the development of the best regulatory pathways toward reducing CO2 aviation emissions. In Center for Biological Diversity v. U.S. EPA, 794 F. Supp. 2d 151 (D.C. 2011), the federal district court held that the EPA had a statutory duty to make endangerment findings with respect to aircraft engines pursuant to the Clean Air Act. Following a second court decision in Center for Biological Diversity v. EPA, No. 1:10-CV-985 (FJS), 2012 WL 967662 (D.D.C. Mar. 20, 2012), the EPA initiated a proceeding “to determine whether greenhouse gas emissions from aircraft engines cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare” but made clear that this agency action did not represent a rulemaking action establishing GHG emissions standards for aircraft engines. Off. of Air & Radiation, EPA, Memorandum in Response to Petition Regarding Greenhouse Gas Emissions from Aircraft (June 14, 2012).
The EPA finally adopted GHG standards for airplanes used in commercial aviation and large business jets in 2020. These standards aligned with international airplane CO2 standards previously adopted by the ICAO in 2017 and were the subject of California v. EPA, 72 F.4th 308 (D.C. 2023). In February 2024, the FAA adopted a final rule to reduce carbon pollution emitted by most large airplanes in flight within U.S. airspace, requiring the incorporation of improved fuel-efficient technologies for airplanes manufactured after January 1, 2028, and for subsonic jet airplanes and large turboprop and propeller airplanes not yet certified. 89 Fed. Reg. 12,634 (Feb. 16, 2024).
While half the global population contributes to aircraft emissions by flying, 1% are responsible for half of global aviation emissions. Olivia Milman, A 17-Minute Flight? The Super-Rich Who Have “Absolute Disregard for the Planet,” The Guardian (July 21, 2022). These 1% make up a small, yet wealthy population that utilizes private jets for both short and long flights. For example, between January 2022 and August 2022, Taylor Swift’s private jet has taken flight 170 times, totaling approximately 8,293 tons of CO2 emissions. Gabriella Godlewski, Private Jet Use by Celebrities Causes Climate Crisis to Soar to New Heights, 11 Joule: Duq. Energy & Env’t L.J. 5 (2023). Private jets, like those utilized by Swift, generally carry fewer passengers for shorter distances—making them 5 to 14 times more polluting than commercial planes per passenger. Id.
Short private flights are much more energy inefficient than longer flights or alternative forms of transportation because these jets burn the most fuel upon takeoff. For example, in an analysis of a proposed expansion of the Laurence G. Hanscom Field airport in Bedford, Massachusetts, to accommodate a 300% increase in private jet services, the private jet flyers on the 20 most active jets at this airfield took 3,240 flights within an 18-month period, accounting for an estimated 14,930 tons of carbon emissions. In contrast, the average American produces 14.8 metric tons per year in total emissions, and the average Massachusetts resident produces only 8 tons per year. Chuck Collins et al., Hanscom High Flyers: Private Jet Excess Doesn’t Justify Airport Expansion (Oct. 2023). The decision to travel by private jet has incredible impacts on the climate crisis, yet the federal government has done little to curb this 1% private air travel, such as by imposing taxes on private jet purchases or charters, flights that travel minimal distances or with few passengers, or incentivizing hybrid-electric jets over fossil-fuel-powered private planes. Id.
In 2017, the ICAO adopted aircraft CO2 standards as the first globally agreed-upon measure of carbon standards for aircraft fuel burn, which helps gauge technological advances within the aviation industry, such as the addition of wingtip devices and newly developed combustion engines. As fuel efficiency can decrease fuel consumption, fuel efficiency gains can moderate growth in U.S. aircraft carbon emissions. However, the extent of carbon emissions emitted throughout a flight is dependent on several factors, some of which can be controlled (i.e., aircraft type) and some of which cannot (i.e., weather conditions). To date, fuel efficiency–related policy actions, use of aviation biofuels, and increased development of electrified aircraft have been the industry’s current approach to curbing carbon emissions from aircraft.
Generally, policy action taken within the aviation industry has sought to make improvements in fuel efficiency, by replacement of older aircraft with newer, fuel-efficient designs and improving logistics and operations to carry more passengers per flight and flying directly to intended destinations. However, updating older aircraft models with energy-efficient technologies or replacing entire fleets with newer models may not be financially viable or technically feasible (depending upon aircraft age and fleet use patterns) for airlines. Further, while increasing cabin density has the potential to decrease fuel use (0.83% fuel savings with every 1% increase in seat capacity for short- and medium-haul aircrafts), this option may not be marketable for post-pandemic travelers less willing to fly in cramped cabin space. Y.Y. Lai et al., Analysing the Opportunities and Challenges for Mitigating the Climate Impact of Aviation: A Narrative Review, 156 Renewable & Sustainable Energy Revs. 111972 (2022).
Recently, the aviation industry has committed to reaching net-zero carbon emissions by 2050, mostly through use of“sustainable” aviation fuels, or SAF. The Inflation Reduction Act of 2022 provided a generous tax credit for fuels that can reduce GHG emissions by 50% as compared to petroleum jet fuel. In December 2023, federal guidance was released suggesting that tax credits for fuel derived from corn ethanol or vegetable oils may be eligible, despite clear evidence that these crop-based fuels both increase net life-cycle emissions and take needed cropland away from food production. Powering airplanes with crops is inherently inefficient and unsustainable (i.e., 1.7 gallons of corn ethanol are required for 1 gallon of SAF) and will have lasting effects on food security and forests worldwide that currently operate as carbon sinks. Dan Lashof & Audrey Denvir,Under New Guidance “Sustainable” Aviation Fuel in the US Could Be Anything But, World Resources Inst. (Dec. 20, 2023). To achieve the U.S. goal of 35 billion gallons of ethanol-based SAF, 114 million acres of corn would be needed—more than 20% of the total area currently planted within the United States. Id.
The challenge to reduce carbon emissions is complicated by technological limitations of electrified aircraft. Electric aircraft can be used effectively for certain uses such as aerial surveying, agricultural inspections, disaster response, military surveillance, flight training, delivery of high-value cargo (i.e., medical shipments, overnight delivery), and air mobility needs (ranging from military personnel movements, to remote community mobility, commuter service, and corporate travel). Electrifying aviation could create significant emissions reductions, noise reduction, and reduced congestion and travel time/costs.
Currently, electric aircraft can hold up to six passengers and maintain an average flight time of under an hour on a single charge. Projected uses of commuter air taxis, light cargo flights, and regional air service are being investigated by airlines such as United, which in 2021 announced a partnership with Archer to review short-haul electric aircraft opportunities for flights serving customers traveling from regional airports to its hub locations. In 2023, Archer began producing its four-passenger aircraft, eVTOL, which can travel up to 50 miles and utilize vertical takeoffs and landings. United is anticipating beginning commercial flight electric service in 2025. While commercial electric aircraft are currently in development, including a single-aisle aircraft with 70 seats and electric/hybrid capabilities and a 186-seat all-electric aircraft, neither will be ready for testing until the 2030s.
While batteries are the most common component to store energy onboard an aircraft, they tend to weigh more than the equivalent in fuel, requiring the development of smaller electric motors. However, the low energy density of battery technology is preventing developments in electric aviation, as it ultimately limits the maximum range of aircraft. Additional research in aviation charging technologies will be needed to support electrification of the aviation industry, as aircraft chargers have power ratings exceeding current technology standards and grid impacts of new energy demands brought on by new electric aircraft fleets will need to be analyzed prior to deployment.
In the last decade, the demand for air travel has increased significantly, with revenue, passengers, and kilometers traveled growing over 5% per year. Despite COVID-19 impacts on global air travel, the demand for international air travel is estimated to continue to grow over the next 20 years. Travel volume, or passenger kilometers traveled per inhabitant per year, is affected by how many people travel and institutional factors that impact such travel (i.e., government regulations or social travel obligations). Generally, initiating and continuing American behavioral and cultural change to reduce air travel has proven difficult.
A common regulatory approach to the challenge of reducing emissions is to create reductions in travel volume through aviation ticket taxes, which indirectly seek to minimize environmental impacts by impacting passenger demand. To date, at least 14 countries have imposed this tax in Europe, including Sweden. In Sweden, the tax is levied on each departing passenger and the final cost of the ticket is based on distance of travel; the tax is technically paid by airlines but passed through to passengers through air ticket pricing. However, there is limited evidence that national regulatory imposition of aviation ticket taxes reduces travel volume or decreases aviation emissions—in fact, ticket taxes have been criticized for simply relocating air passengers to airports in neighboring countries with lower ticket prices. Ticket taxes also have been criticized for being used by countries for general budget considerations, instead of incentivizing the aviation industry to decrease emissions or, alternatively, to fund non-aircraft-related climate change mitigation measures.
Another tax-based approach to air travel emission reductions is the allocation of taxes based upon estimated emissions per airline passenger. Within the industry, the conventional approach to allocating passenger emissions is based on passenger space requirements within the aircraft. These routine passenger emissions calculations are already utilized for airline GHG emissions and carbon offset schemes. As aircraft operations depend upon profitability (i.e., high fares from late bookings), premium class passengers are generally assigned1.3–2.9 times more emissions per unit of distance than economy class passengers, which subsequently impacts ticket prices.Stijn van Ewijk et al., Estimating Passenger Emissions fromAirfares Supports Equitable Climate Action, 18 Env’t Rsch. Letters 024013 (2023). Yet, in a study published last year estimating passenger emissions from airfares, scientists found that a tax on fare-based emissions (assigning emissions proportional to airfares) instead of space-based emissions led to a more even distribution upon low-fare and high-fare travelers. Id. Thus, air ticket tax schemes using a fare-based emissions analysis may be more equitable in more accurately reflecting the drivers of aviation emissions. However, while this tax approach would help achieve equitable climate action within the aviation decarbonization space, it is unlikely to be adopted within the United States as such an approach is anticipated to decrease airline revenue.
The primary solution to reducing GHG emissions within the aviation sector is the replacement of air travel with alternative modes of travel. Though this would not be feasible for international travel, there are significant implications for carbon reductions if Americans shifted from domestic air travel to rail travel. However, this cultural shift will likely depend upon rail travel times to a destination, and less so on other factors such as frequency or price. Thus, for an American to intentionally choose rail travel over air travel, domestic travel routes by rail would have to be significantly shortened. Reduction of air travel volumes also could occur by mixed-modes, such as combinations of rail and air (especially for short-haul flights) by reducing air travel distance coupled with moderate increases in air travel time. Yet considering the lack of high-speed rail availability and infrastructure throughout the nation, this air emissions mitigation solution is not yet feasible for the American public.
While GHG emissions are generally allocated to individual passengers based on space availability and travel class, aircraft operations are generally focused on profit margins instead of environmental impacts. Carbon offsets for international aviation attempt to offset the growth of air travel emissions but do not come close to aligning with globally agreed-upon emission reductions within the aviation industry.
Climate planning needs to address aviation emissions, as the industry cannot place carbon emissions reduction obligations solely on the shoulders of individual commercial flight passengers. Tax-based approaches on short-haul flights, especially within the private jet travel sector, should be explored to ensure continued access to flight travel by low-fare commercial travelers. While electrification of the aviation industry will be crucial to reach net-zero emissions goals, continued use of sustainable aviation fuels is unsustainable in the long term and investments into modal shifts such as high-speed rail and incentivizing mixed-mode transportation will be necessary in state and national climate planning efforts.
