Carbon offsets alone will not make flying climate friendly

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Jet A-1, one The straw-colored kerosene fuel used in most large aircraft is a difficult substance to replace. It’s full of energy; per unit weight, at least 60 times more than the lithium-ion batteries used to power electric cars. It is also terrible for the climate. So while the aviation industry has gradually joined global pledges to get rid of carbon emissions, it has mostly promised to repair its damage elsewhere – through offsets that could involve planting trees, restoring wetlands or paying people to preserve ecosystems that otherwise have been razed. But according to a growing body of research, these efforts leave something out: most of the global warming effects of flight are not due to carbon dioxide.

Burning jet fuel at 35,000 feet sets off a molecular cascade in the troposphere. The initial combustion releases a shower of particles: sulphur, nitrogen oxides, soot and water vapour. At these frigid heights, some of the particles become nuclei around which condensation gathers and then quickly freezes, helping to produce puffy contrails that disappear or persist as wispy cirrus clouds at high altitudes. In the presence of sunlight, nitrogen molecules set off a chain of reactions that produce ozone and destroy free-floating atmospheric methane. It is difficult to pinpoint the meaning of all this alchemy. Some of these reactions, such as the destruction of methane, contribute to the cooling of the Earth. Others warm it up. It all depends on the atmospheric conditions of each flight, multiplied by the tens of thousands of planes criss-crossing the skies every day.

Overall, the warming effects add up. In analysis published last year, an international team of researchers attributed 3.5% of total warming in 2011 to aviation alone, which may not seem like much, but the number has been growing rapidly. The authors found that about two-thirds of the warming due to aviation at that time was caused by all these factors which are not CO2 emissions.

That’s why some scientists argue that the term “carbon neutral” doesn’t mean much, at least when it comes to jet aircraft. If the aviation industry wants to do its part to help meet global temperature goals, it’s better still to think in terms of “climate-neutral,” says Nicoletta Brazzola, climate policy researcher at ETH Zurich. In a study published this week in Natural climate change, she outlines all the ways to get there, including rules for more efficient flight, new technologies like low-carbon fuels and batteries, and more intensive efforts to remove carbon from the air that would go beyond aviation CO cancellation2 emissions, accounting for all industry warming effects. And, oh yeah: less theft. “It would take a huge effort to meet this climate-neutrality framework only with technological fixes and no lifestyle changes,” she says.

So far, the industry has focused on offsetting carbon emissions. It’s the greenhouse gas we’re all familiar with, and it’s pretty easy to measure how burning jet fuel translates into tons of carbon emissions. This is based on an intimate knowledge of existing fuels and engines. Airlines already do those calculations and let customers see their damages and often pay a little extra to offset those emissions through partner programs that do things like plant trees. Expecting continued growth in demand for aviation, members of the International Civil Aviation Organization (ICAO) have pledged to maintain their net carbon emissions at 2019 levels through these types of offsets. . This effort itself is far from perfect –a Number of surveys found that many of the offset programs that airlines partner with chronically overestimate the amount of carbon they manage to store. And again, these programs are all about carbon.

This is partly because it is difficult to account for all elements without CO2 The factors. Atmospheric chemistry at 35,000 feet is inherently localized and dependent on factors such as temperature and humidity. The biggest uncertainty is the potential behavior of contrails – the tendrils that form behind planes as water molecules condense around exhaust particles and freeze. “The basic microphysics of ice crystals is quite difficult to master,” says David Lee, an atmospheric scientist at Manchester Metropolitan University who studies aviation emissions. If the air is moist and cool enough, they can hang around as cirrus clouds, which would likely have a net warming effect. Time of day is another X-factor. During the day, these clouds can reflect sunlight, keeping Earth cool. But they can also trap heat, especially at night.

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