Reducing air travel by small amounts each year could level off the climate impact

Many world leaders and delegates will have traveled to Glasgow to take part in COP26, which is the 26th UN climate change summit in person. However, as they debate emissions targets that keep global warming under 1.5degC but not 3degC or greater, aviation is not likely to be a part of them because of the lack of alternatives that are low carbon for long-haul flights.

However, it is. In a new study with my colleagues, I estimated that if the aviation industry continues to expand at the current rate, the consumption of jet fuel will add 0.1@C on global warming in 2050. This is the majority of it up to now and the rest over the coming three decades.

Aviation is the cause of 4 percent of the 1.2degC rise in global mean temperature we’ve witnessed in the past since industrialization. If we do not take action to cut down on flights, the industry will contribute 17 percent of the 0.3degC left to reach the 1.5degC temperature goal and 6 percent of the 0.8degC left to remain within the 2°C limit. Airliners contribute more carbon dioxide to the atmosphere than the majority of nations.

Warming footprints

At the rate we are at, the planet will be warming by 2 degrees Celsius within the next three years. To determine how various activities contribute to warming, scientists study carbon emissions. This is because the amount it takes for the Earth gets warmer is proportional to the cumulative carbon emissions from the atmosphere. This is an excellent estimation in many instances; however, it’s not accurate when it comes to emissions from aeroplanes that travel at altitudes of up to 12 kilometers.

In addition to CO2, aircraft engines release Nitrogen oxides as well as water vapor sulfur and soot, which can cause contrail clouds of cirrus and other complex chemical reactions that occur in the atmosphere. The sum of these non-CO2 impacts adds more heat over CO2 emissions. Thus, the footprint of warming caused by aviation is anywhere between two and three times more than the conventional carbon footprint.

Condensation trails caused by engines in aircraft can contribute to global warming. MichaelGaida/Pixabay, CC BY

While a significant portion of the CO2 emissions from a flight remain in the air for thousands of years, The non-CO2 effects decrease as time passes, vanishing within about 10 years. Therefore, any increase in the aviation industry, as measured by the global consumption of jet fuel, is a bigger impact since both CO2 and non-CO2 impacts are a part of the same equation.

However, a drop in the aviation industry can partially stop some warming as CO2 effects that are not carbon dioxide disappear in time until only CO2 effects are left. Consider the non-CO2 effects in bathtubs – they fill up as the taps are turned further, despite a steady discharge from the plughole. The same bathtub can eventually fill up if the taps are slowly turned down.

The non-CO2 effects of flying on the earth’s atmosphere will gradually disappear as fewer and smaller flights are made in order that the contribution of aviation to warming eventually decreases. In this scenario, the rise in CO2 emissions will offset the decrease in non-CO2 impacts. While aviation will still be a contributor to warming, the total warming caused by both will remain constant in time. What amount of aviation would it require to shrink to lessen its impact on global warming?

Our analysis shows that flying does not have to stop right away to stop the global warming caused by aviation from increasing. Air travel has caused 0.04degC of warming so far. With a reduction of 2.5% of jet fuel consumption, which is currently only feasible through cuts in the flow of air traffic, this warming is likely to remain at an unchanging rate in the coming decades.

Do we really need to fly?

COVID-19 had a major impact on aviation. The air traffic is currently 10% to 20% below levels prior to the pandemic, but it is recovering quickly. Polities should shift subsidies towards more environmentally sustainable forms of transport, including trains. There’s a lot more that could be done.

Changes in the way people fly because of the pandemic have caused some to reduce their flights. Dmncwndrlch/Pixabay, CC BY

Lockdowns and the move to remote work have made a number of people reconsider the need for flying. People who are deciding to reduce their travel will significantly reduce the amount of unnecessary flights. The combination of in-person and online participation in hybrid meetings, whenever feasible, is a fantastic method to help support this shift.

The reduction in the space that the business class takes up on aircraft is another method to reduce flight times because it lets more passengers be on one flight.

The decision not to allow airport expansions could have a significant impact. In the UK, there is a Climate Change Committee, an expert body that advises the UK government on climate change, which has urged not to expand airports to ensure that they are aligned with the climate goals. But expanding Heathrow Airport is being planned for the future.