The climate impact could be reduced by reducing air travel in small increments each year.

Aerial engines were still burning just before the pandemic. one billion litresFuel costs per day. The number of civil aviation flights per day dropped to a record low in the 1990s. 110,000In 2020, the average number of passengers will be less that 50,000. Air traffic is returning to pre-pandemic levels, as travel restrictions are being relaxed.

Most world leaders and delegates will have flown to Glasgow to attend COP26 – the 26th annual UN climate change summit – in person. But as they haggle over emissions targets to limit global warming to 1.5°C, and not 3°C or moreBecause of the inability to find low-carbon alternatives for long-haul flights, aviation is unlikely that they will be included.

It should. In new research, my colleagues and I calculated that if the aviation sector continues to grow on its present trajectory, its jet fuel consumption will have added 0.1˚C to global warming by 2050 – half of it to date, the other half in the next three decades.

Aviation is responsible for 4% of the 1.2°C rise in the global mean temperature we have already experienced since the industrial revolution. Without action to reduce flights, the sector will account for 17% of the remaining 0.3°C left in the 1.5°C temperature target, and 6% of the 0.8°C left to stay within 2°C. Global warming is being exacerbated by airlines. than most countries.

Warming footprints

At the current rate, the world will have warmed by 2°C within three decades. Scientists measure carbon emissions to quantify the contribution of different activities to global warming. Because the Earth’s temperature is proportional to the amount of carbon dioxide in the atmosphere, scientists measure carbon emissions. This is a good approximation for many cases, but it’s inaccurate for emissions due to aeroplanes travelling at altitudes greater than 12 kilometres.

As well as CO₂, aircraft engines emit nitrogen oxides, water vapour, sulphur and soot, causing contrail cirrus cloudscomplex chemical reactions in the atmosphere. The sum of these so-called non-CO₂ effects adds more warming on top of the CO₂ emissions. The total aviation warming footprint is two to three times larger than a conventional carbon footprint.

While a large share of a flight’s CO₂ emissions remain in the atmosphere for many thousands of years, the non-CO₂ effects diminish over time, vanishing within about ten years. So any growth in aviation, measured in global jet fuel consumption, has an amplified impact as both CO₂ and non-CO₂ effects add up.

But a decline in aviation can partly reverse some warming, as the non-CO₂ effects disappear over time until only the CO₂ effects remain. Think of the non-CO₂ effects like a bathtub – it fills up when the taps are turned further and further, despite a slow outflow down the plughole. However, the bathtub will eventually stop filling up if the taps get turned down slowly.

The non-CO₂ effects of flights on the atmosphere will slowly disappear if fewer and fewer flights are taken, so that aviation’s contribution to warming eventually levels off. In that situation, the increase from continued CO₂ emissions would balance the fall in non-CO₂ effects, and although aviation would still contribute to climate change, the total warming from both would remain constant over time. How much would the aviation industry need to shrink in order to reduce its impact on global warming?

Our calculations show that flying does not need to stop immediately to prevent aviation’s contribution to global warming expanding. Flying has already caused 0.04°C of warming to date. However, with a yearly drop of 2.5% in jet fuel usage, which is currently only possible through cuts in air traffic, this warming should remain constant over the next decades.

When is it really necessary to fly?

COVID-19 had a significant impact on the aviation industry. Although air traffic is still below pre-pandemic levels by approximately 10-20%, it is increasing. rebounding quickly. Politicians should shift subsidies from flying towards more sustainable modes of transport like train journeys. There is more to be done.

Many people are now questioning the necessity of flying due to lockdowns and shift to remote work. Resolving to fly less can help reduce unnecessary flights. It is possible to support this shift by combining virtual and in-person attendance in hybrid meetings whenever possible.

Reduced space for business classes on aeroplanes can also be a way to reduce the number flights. It allows more passengers to travel in one flight.

It could also have a significant impact on the future of airport expansions. The UK’s Climate Change Committee, an expert body which advises the UK government, has recommended not expanding airportsto align the sector and climate targets. The expansion of Heathrow airport is still underway. planned to go ahead.

While sustainable aviation fuels and electric planes are being researched, none of these technologies are yet available on a large enough scale. If the aviation industry aims to return its pre-pandemic rate, it has little chance of meeting climate targets.

This story is part of The Conversation’s coverage on COP26, the Glasgow climate conference, by experts from around the world.

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