Aviation’s impact on global warming has doubled in the past two decades, according to a new study.
Using computer models, researchers found flying is responsible for about 3.5 percent of humanity’s contribution to climate change, and two-thirds of that is from contrails and other non-CO2 emissions.
The team calculates that between 1940 and 2018, the worldwide aviation industry generated 26 billion tons of carbon dioxide – half of which was generated in the last 20 years.
Although plans had been grounded during the coronavirus pandemic, experts warn that the near-total shutdown will have minimal impact in the long run.
Research published this month in the journal Atmospheric Environment offers the first comprehensive environmental analysis of the aviation industry using a new metric called ‘effective radiative forcing’ (ERF).
ERF calculates the increase or decrease in the energy coming from the sun and the energy emitted from the Earth since the pre-industrialized era.
It factors in non-CO2 emissions like contrails, water vapor and nitrous oxide, and allows aviation’s impact on climate change to be compared to other sectors, like shipping and ground transport.
‘There are many different components of aviation’s large impact on climate change, said co-author Laura Wilcox, an atmospheric scientist with the National Center for Atmospheric Science, ‘but the positive side of that is it provides us with many ways we can make changes to mitigate it.’
Using computer models, the researchers found that flying is responsible for 3.5 percent of the global-warming effect resulting from human activities.
That statistic has remained constant since 2000, says lead author David Lee, director of the Center for Aviation, Transport, and the Environment at Manchester Metropolitan University, but only because other sources have increased so dramatically.
Over the same period, the warming effect from flying has nearly doubled.
Lee calculates that between 1940 and 2018, the worldwide aviation industry generated 26 billion tons of carbon dioxide, half of which was generated in the last 20 years.
To date most efforts to curtail flying’s impact on the environment have focused on lowering that rate.
In July, for example, JetBlue announced it was offsetting CO2 emissions from jet fuel on domestic flights with various global partnerships.
But contrails, formed by the soot and exhaust fumes spewed out by jet engines, have an even greater effect.
They and other non-CO2 emissions are responsible for two-thirds of the industry’s impact on climate change, according to the new report.
Contrails are formed at high altitudes when water vapor condenses and freezes around jet exhaust.
These artificial ‘clouds’ can linger for seconds or hours, depending on the temperature and humidity, and their impact is complex and sometimes contradictory.
Contrails warm the planet by reflecting heat back down to Earth, but they also have a lesser cooling effect by reflecting sunlight back into space.
They’ve been blamed for everything from severe weather phenomenon to respiratory illnesses to homosexuality.
While those conspiracy theories have been widely disproven, scientists say contrails’ effect on global warming is not being seriously addressed.
The 2016 Paris Agreement on climate change doesn’t include non-CO2 emissions like contrails. (It also doesn’t cover international aviation, which accounts for 64 percent of all air traffic.)
And while flying is down significantly because of the coronavirus, “As the COVID-19 pandemic changes, aviation traffic is likely to recover to meet projected rates on varying timescales,’ Lee said.
Re-routing flights could help avoid creating contrail cirrus but would mean longer flights and more fuel burnt, producing more greenhouse gas emissions.
‘The non-CO2 warming is the elephant in the room,’ Bill Hemmings of Transport & Environment told New Scientist in 2019. ‘The attitude has been that there are uncertainties, so let’s sit on our hands and do nothing.’