Even “net zero” aviation can still cause significant global warming

Efforts to make flying greener only account for carbon dioxide emissions, but modeling shows this ignores 90 percent of future flights’ contribution to climate change

from Adam Vaughan

Future flights will threaten the goals of the Paris climate agreement if efforts to achieve net-zero aviation fail to account for the warming effect of streak clouds created by aircraft, a study has found.

The research comes just days after the UK government announced it Jet Zero Strategy on July 19thwith the aim of reducing carbon emissions from flights to zero by 2050.

Nicoletta Bratzolaat ETH Zurich in Switzerland and her colleagues found that even if such efforts to reduce carbon emissions succeed, the global aviation sector could raise average global temperatures by between 0.1°C and 0.4°C. As the world has already warmed by 1.1°C since the industrial revolution, Brazzola’s team says that further warming could compromise the Paris Agreement’s goal of holding the temperature rise to 1.5°C.

The warming comes from the ways in which flights heat the atmosphere beyond the carbon dioxide released by burning jet fuel, which are the only emissions currently accounted for by international and most national efforts to decarbonize aviation . The main of these non-CO₂ the effects are the contrails that form due to the soot, aerosols and water vapor emitted by aircraft engines.

“We found that the mitigation efforts needed to get aviation to a place where it is compliant with the Paris Agreement are enormous,” says Brazzola.

Her team studied various future scenarios for the search for flights, technologies to power them and how much CO2₂ would have to be removed from the atmosphere by trees or machinery to reach net zero. “Without very strong reductions in demand, and without very rapid, almost unfeasible shifts to clean technologies, we’re going to have to scale up decarbonization to a very large extent anyway,” she says.

The team’s modeling suggests that the non-accounting of aviation non-CO₂ effects, as most politicians would ignore 90 percent of the contribution of future flights to climate change.

Paul Williamsat the University of Reading, UK, says: “This new study makes a compelling case for moving away from carbon-neutral aviation as a primary policy objective and focusing instead on climate-neutral aviation. It would be a radical change of direction, but I think it’s long overdue.”

The study shows that new fuels and technologies for flight, from hydrogen to batteries, will need to be developed and deployed quickly to have any chance of achieving climate neutrality.

It also suggests that the aviation sector’s signature short-term plan to reduce its impact on climate change – a carbon offset scheme that was watered down during the pandemic – will not be enough.

Her team found that even with only a modest increase in flight demand, the status quo of jet fuel and offsets would require an area the size of Germany to be planted with trees to offset aircraft emissions. This amount of CO₂ removal is very large and may not be feasible, she says.

“Continuing to fly passenger jet fuels and offsetting carbon removal is a very unviable path,” says Bratzola. The results also show how difficult it will be to meet this new target without curbing the world’s future appetite for more flights, she added.

Journal reference: Nature Climate Change, DOI: 10.1038/s41558-022-01404-7