A century after the first commercial flight, the aviation industry has become a fixture of global transport…and of global emissions. Today, some 20,000 airplanes are in service around the world, producing at minimum 2.5 percent of annual emissions. With upwards of 50,000 planes expected to take to the skies by 2040—and take to them more often—fuel efficiency will have to rise dramatically if emissions are to be reduced.
This can be accomplished by:
- Adopting the latest and most fuel-efficient aircraft;
- Retrofitting existing aircraft with aerodynamic winglets, better engines, and lighter interiors;
- Retiring older aircraft early; and
- Operating existing aircraft with fuel-saving practices.
More dramatic redesigns of airplane bodies and sustainable jet fuels, such as those made from algae, are in development. Along with national and international regulation of the airline industry, they may help address the greenhouse gases that trail movement by flight.
first commercial flight: Associated Press. “Airline Group Marks 100 Years of Commercial Flight.” NBC News, June 2, 2014.
plane tickets…sold: “In Flight: See the Planes in the Sky Right Now.” The Guardian. January 21, 2014
air freight volume: Airbus. Mapping Demand: Global Market Forecast 2016-2035. Airbus, 2016.
airplanes…in service: Airbus, Mapping; Boeing. Current Market Outlook: 2015-2034. Boeing, 2015.
[airline] annual emissions: Lee, D.S., et al. “Aviation and Global Climate Change in the 21st Century.” Atmospheric Environment 43 (2009): 3520–3537; Schafer, A.W., et al. “Costs of Mitigating CO2 Emissions from Passenger Aircraft.” Nature Climate Change, 6, no. 4 (2016): 412-417.
planes [in] the skies by 2040: Pearce, Fred. “After Paris, A Move to Rein in Emissions by Ships and Planes.” Yale Environment 360. May 19, 2016.
fuel…operating costs: Grose, Thomas K. “Reshaping Flight for Fuel Efficiency.” National Geographic. April 23, 2013.; Stalnaker, Tom, et al. Airline Economic Analysis: 2015-2016. Oliver Wyman, 2016.
fuel efficiency of domestic flights; international flights: Grose, “Reshaping.”
high rates of air bypass: BDL. Report 2014—Energy Efficiency and Climate Change, Berlin: Bundesverband der Deutschen Luftverkehrswirtschaft (German Aviation Association), 2015.
Pratt & Whitney…turbofan engine: Grose, “Reshaping.”
Rolls-Royce…lightweight engines: BDL, Report 2014.
“winglets” and…“sharklets”: BDL, Report 2014; Davies, Alex. “Planes Have to Get More Efficient. Here’s How to Do It.” Wired. June 11, 2015.
split scimitar winglets: BDL, Report 2014.
Boeing and NASA…aircraft: Boeing. “Blended Wing Body Back to the Tunnel.” Boeing, September 7, 2016.
wing design with a brace: NASA. “Slimmed Down Aircraft Wing Expected to Reduce Fuel and Emissions by 50%.” National Aeronautics and Space Administration. November 9, 2016.
dramatic redesigns…efficiency gains: Grose, “Reshaping.”
taxiing on a single engine: Deonandan, Indira, and Hamsa Balakrishnan. “Evaluation of Strategies for Reducing Taxi-out Emissions at Airports.” 10th AIAA Aviation Technology, Integration, and Operations (ATIO) Conference, Fort Worth, Texas, 2010.
continuous and late descent: BDL, Report 2014.
airline captains…fuel efficient practices: Gosnell, Greer K., John A. List, Robert Metcalfe. A New Approach to an Age-Old Problem: Solving Externalities by Incenting Workers Directly. NBER Working Paper No. 22316. Cambridge, M.A.: National Bureau of Economic Research, 2016.
sustainable aviation fuels: Rocky Mountain Institute. “Sustainable Aviation.” http://www.rmi.org/sustainable_aviation_fuels.
fuel efficiency and airline profitability: Zeinali, Mazyar, Daniel Rutherford, Irene Kwan, and Anastasia Kharina. U.S. Domestic Airline Fuel Efficiency Ranking 2010. Washington, D.C.: International Council on Clean Transportation, 2013.
Carbon Offset and Reduction Scheme for International Aviation: Milman, Oliver. “First Deal to Curb Aviation Emissions Agreed in Landmark UN Accord.” The Guardian, October 6, 2016.
The pollutants that trail movement by flight—carbon dioxide, nitrogen oxides, water vapor in contrails, black carbon—are not.
Those gains were largely thanks to fleet upgrades, while airlines also sought to maximize the number of passengers on each plane.
Project Drawdown defines the airplanes solution as: the increased use of technologies to reduce aircraft fuel burn. This solution replaces conventional aircraft with existing global fleet-wide fuel efficiency.
Air travel is estimated to cause approximately 2.42 percent of manmade carbon dioxide emissions in the world (BDL, 2014). However, its expansion is causing increasing alarm. Airplane fuel efficiency efforts aim to reduce fuel use per passenger-kilometer of air travel. Though freight-only aircraft fuel efficiency is not analyzed here, part of the impact on air freight fuel use is accounted for in the large fraction of total air freight that is carried in the belly of passenger aircraft. 
As there are numerous technologies and operational approaches for reducing airplane fuel use, only the most impactful technologies in use today to improve fuel efficiency were included in this study. Therefore, well-publicized but non-commercial technologies such as aviation biofuels were excluded.
This analysis includes the newest, most fuel-efficient aircraft (called “intermediate generation”),  as well as the use of fuel efficiency retrofits to existing aircraft. Intermediate generation aircraft are expected to be 15-20 percent more fuel-efficient than earlier models, in part as a result of more fuel-efficient engines, new wingtip devices,  and light weighting approaches. Research suggests that the combination of these three technologies in a retrofit would amount to efficiency improvements comparable to a newer aircraft model. In this study, new and retrofitted aircraft are compared to conventional aircraft with the existing global fleet-wide fuel efficiency.
Total Addressable Market 
The total addressable market for airplanes is measured in terms of total interurban passenger travel by air, projected for every year of analysis (2020-2050), in billion passenger-kilometers. Current adoption  was taken as the total passenger-kilometers provided by existing intermediate generation aircraft, in the single-aisle and twin-aisle categories.
Projected adoption of fuel-efficient aircraft was based on the expected production of intermediate generation aircraft, according to published delivery rates of major suppliers.  Delivery rates were assumed fixed for each aircraft type.
Adoption Scenarios 
Impacts of increased adoption of airplanes from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the existing fraction of higher-efficiency aircraft remains constant.
- Plausible Scenario: Fuel burn is improved by 15 percent, Boeing and Airbus supply aircraft at their published rates, and aircraft older than 24 years are retired.
- Drawdown Scenario: Aircraft delivery rates and retirement remain the same as in the Plausible Scenario. However, a third supplier is included that produces new, comparable single-aisle aircraft by 2025 and twin-aisle aircraft by 2035.  Additionally, fifty aircraft are retrofitted annually.
- Optimum Scenario: This scenario differs from the Drawdown Scenario in only two key ways: 1) efficient aircraft are assumed to take more passengers (a higher load factor of 90 percent, compared to 80 percent in other scenarios); 2) fuel burn is reduced by 18.3 percent. Everything else remains the same as in the Drawdown Scenario, including the existence of an additional supplier.
Emissions for each scenario were estimated using the fuel emissions factor taken from the Intergovernmental Panel on Climate Change (IPCC) guidelines, and applied to fuel consumption data from the International Council on Clean Transport (ICCT).
Costs of adopting the intermediate generation aircraft are reported as the additional cost compared to adopting aircraft with average fleet efficiency. For each intermediate generation aircraft, an equivalent conventional aircraft was priced and the price difference was derived.  The average difference for single-aisle aircraft was around US$11 million,  and that of twin-aisle was US$40 million.  Operating costs, which included fuel costs, were derived using historical data from the International Energy Agency (IEA).  The solution’s operating costs were reduced by the efficiency improvements noted above.
To prevent double-counting, steps were taken to ensure that the total travel demand of all non-urban passenger Transport Sector solutions remained below the projected total non-urban travel demand.
In the Plausible Scenario, a potential reduction of 5.05 gigatons of carbon dioxide-equivalent greenhouse gas was found from 2020-2050, which corresponds to a 63 percent adoption rate by 2050. Net costs over that time would be US$662 billion above the conventional approach. Efficiency improvements are estimated to bring operating savings of US$3.2 trillion, however. For the Drawdown Scenario, the emissions avoided amounted to 5.2 gigatons with 80 percent adoption; the Optimum Scenario would result in 6.5 gigatons of emissions reduced.
The use of more efficient aircraft is desirable for airlines in times of higher fuel prices. It would have direct bottom-line impacts, as fuel often represents a third of operating costs. For much of 2016, however, fuel prices were low, and there is no assurance that prices will return to their previous levels of almost three times higher. Nevertheless, Project Drawdown’s calculations indicate a large buffer in operating savings and marginal costs that make the investment in fuel-efficient aircraft financially viable for airlines at lower fuel prices. Using Jet A fuel prices of March, 2017, the operating savings are still high at US$1.2 trillion for the Plausible Scenario.
There are limitations to this approach. For example, the potential of other technologies being implemented was excluded in this study.  Also, the Reference Scenario conservatively assumes fixed fleet efficiency. These limiting assumptions were made to show the impact of existing technologies on the airline industry. The results indicate that airlines have a role to play in the planet reaching the point of drawdown.
 According to Airbus, belly freight is about 52 percent of all air freight.
 Including the 787, 777X, and 737MAX family of Boeing, and the A320neo family, A330neo family, and A350XWB of Airbus.
 Also called “winglets” or “sharklets”, these devices cannot be installed on all older aircraft due to lack of sufficient wing strength and other limitations.
 For more on the Total Addressable Market for the Transport Sector, click the Sector Summary: Transport link below.
 Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2014 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.
 Delivery of a single-aisle aircraft is assumed to provide 247 million passenger-kilometers, and a twin-aisle aircraft 840 million passenger-kilometers, of adoption.
 For more on Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Transport Sector-specific scenarios, click the Sector Summary: Transport link.
 This additional manufacturer can represent any or all of numerous nascent options, such as COMAC of China or the UAC of Russia. It produces around 5 percent of all efficient aircraft annually.
 For instance, the Airbus A320neo was considered a more efficient replacement for the A320, and the Boeing 777X-9 was considered a replacement for the 777-300ER. These relationships were determined through web searches for each efficient model.
 All monetary values are presented in US2014$.
 It is assumed that this differential represents the retrofit costs for each aircraft type, and acknowledged that airlines often pay different prices than the list prices due to negotiations that occur with the manufacturers.
 The last ten years of fuel prices were averaged, and this fixed average was used for the future projections.
 For more on Project Drawdown’s Transport Sector integration model, click the Sector Summary: Transport link below.
 The potential for open rotor engines could be large, but estimates seem to indicate availability in the 2030s onwards.