Aviation responsible for 3.5 per cent of climate change drivers

The findings show that two-thirds of the impact from aviation is attributed to non-carbon-dioxide emissions and the rest from CO₂.

Researchers evaluated all of the aviation industry’s contributing factors to climate change including carbon dioxide (CO₂) and nitrogen oxide (NOx) emissions, and the effect of contrails and contrail cirrus – clouds of ice crystals created by aircraft jet engines at high altitude.

This was analysed alongside the water vapour, soot, and aerosol and sulfate aerosol gases – fine particles suspended in the air – found in the exhaust plumes emitted by aircraft engines.

The researchers said it is the first complete set of calculations for aviation that uses a new metric introduced in 2013 by the Intergovernmental Panel on Climate Change.

This metric is called ‘effective radiative forcing’ (ERF) and represents the increase or decrease since pre-industrialisation times in the balance between the energy coming from the Sun and the energy emitted from the Earth, known as the Earth-atmosphere radiation budget.

Using the new ERF metric, the team found that contrail cirrus’ impact is less than half than that estimated previously but still the sector’s largest contribution to global warming, by reflecting and trapping escaping heat from the atmosphere.

Carbon dioxide emissions represent the second largest contribution but unlike the effects of contrail cirrus, CO₂’s effect on climate lasts for many centuries.

“Given the dependence of aviation on burning fossil fuel, its significant CO₂ and non-CO₂ effects, and the projected fleet growth, it is vital to understand the scale of aviation’s impact on present day climate change, especially in view of the requirements of the Paris Agreement to reach ‘net zero’ CO₂ emissions by around 2050,” lead author Professor David Lee said.

“But estimating aviation’s non-CO₂ effects on atmospheric chemistry and clouds is a complex challenge for contemporary atmospheric modelling systems.

“It is difficult to calculate the contributions caused by a range of atmospheric physical processes, including how air moves, chemical transformations, microphysics, radiation, and transport.”

Dr Laura Wilcox, an atmospheric scientist at the University of Reading and NCAS, contributed the assessment of water vapour impact to the study.

She said: “There are many different components of aviation’s large impact on climate change, but the positive side of that is it provides us with many ways we can make changes to mitigate it.

“This massive assessment demonstrates the magnitude of the climate-change impact of aviation, and confirms that urgent action is needed to reduce the environmental impact of all travel to avoid very serious impacts to our way of life in the future.”

Professor Lee and his team calculated that the cumulative CO₂ emissions of global aviation throughout the course of the industry’s entire history – defined as between 1940 and 2018 – were 32.6 billion tonnes.

Approximately half the total cumulative emissions of CO₂ were generated in the last 20 years alone, attributed largely to the expansion of the number of flights, number of routes and fleet sizes, particularly in Asia, though partially offset by improvements in aircraft and jet engine technology, larger average aircraft sizes and increasing efficiency in the use of aircraft capacity to fit more passengers in the same space.

The research team estimated the figure of 32.6 billion tonnes accounted for 1.5 per cent of total CO₂ emissions ever at that point.

When the non-CO₂ impacts were factored in, aviation’s was calculated to be 3.5 per cent of all human activities that drive climate change.

Last year, the Committee on Climate Change called on the UK government to try and curb demand for flights in order to reduce greenhouse gas emissions.