Flying low(carbon)

Beyond flight shaming: Scientists propose fix for flying's climate problem

By changing just a small percentage of flight paths, planes' emissions can drop dramatically.

Several aircraft with white contrails

Every year, planes contribute an outsize amount of emissions to the atmosphere, accelerating the rate of global warming. Now, scientists might have devised an easy fix to lower their impact.

In August 2019, climate activist Greta Thunberg took a two-week boat ride and a hard stance against flying. She sailed from the United Kingdom to New York City on an emissions-free yacht to attend the United Nations conference on climate change. She also made a point. Her move spawned a new trend in flight shaming. Celebrities that choose to fly despite claiming green credentials — from the Sussexes to Leonardo DiCaprio — have come to suffer the wrath of the climate conscious.

But a new study suggests there may be another way, a happy medium between trans-Atlantic sails and private jet planes.

Flying planes at a slightly lower altitude and slightly changing their flight paths may reduce their black carbon output dramatically, according to a study published Wednesday in the journal Environmental Science and Technology. That can happen by changing just 1.7 percent of plane altitudes — shifting them to flying either 2,000 feet higher or lower than usual.

The reason why this small fix could work big wonders is to do with contrails.

Cracking the contrail conundrum

Contrails — short for condensation trails — are the thin, fluffy exhaust clouds that planes leave behind, streaking our skies in the process. But as pretty as they may be from the ground, contrails form when planes emit particles of black carbon, allowing moisture to condense, and ice to form on those particles.

A beautiful, climate-damaging contrail.

Taro Hama @ e-kamakura/Moment/Getty Images

The trails generally only linger for a few minutes, but, under the right conditions, they can swirl around with the clouds to form “contrail cirrus” clouds that persist for up to 18 hours. These mega-clouds have a big impact on global warming — the water vapor in the clouds functions as a greenhouse gas. Fun fact: Water vapor is the most abundant of the greenhouse gases.

If the flight paths and plane altitudes of just a handful of all the planes that fly every year are changed, then the effect contrails have on the environment could shrink by about 60 percent, according to the study.

But there is a caveat: Some of these flight diversions may make flights less efficient, meaning planes would release more carbon dioxide.

But by targeting flights with the most powerful contrails and focusing on minor altitude changes, the potential benefits still outweigh the carbon drawbacks, the researchers say. That is because the most problematic contrails come from just a tiny number of overall flights. In Japan, for example, 80 percent of the environmental damage from contrails stems from just 2 percent of flights.

The results jibe with past research suggesting contrails have a significant effect on the climate — but exactly how large a toll they exert is still up for debate.

“Contrail cirrus themselves and their effects on the surface are ongoing topics of research," aerospace researcher Lisa Bock told Inverse in June 2019. "But it’s clear they warm the atmosphere.”

But even if we solve the contrails conundrum, carbon emissions continue to be a major problem for planes.

In 2018 alone, aviation worldwide pumped more than 900 million metric tons of carbon dioxide into the atmosphere, according to the International Council on Clean Transportation.

That figure is only expected to increase — by as much as 700 percent by the year 2050, according to the International Civil Aviation Organization.

So as flight shaming continues to grab headlines — like when Joaquin Phoenix called out celebrities for taking private jets to the Golden Globes — it is unclear how much shame can curb the major emissions predicted ahead.

More efficient aircraft engines will have to be part of the solution, too, the authors on this study say. In fact, combining cleaner-burning planes with their altitude-adjusting methods could lead to an emissions reduction as high as 92 percent, they say.

Abstract: The climate forcing of contrails and induced-cirrus cloudiness is thought to be comparable to the cumulative impacts of aviation CO2 emissions. This paper estimates the impact of aviation contrails on climate forcing for flight track data in Japanese airspace and propagates uncertainties arising from meteorology and aircraft black carbon (BC) particle number emissions. Uncertainties in the contrail age, coverage, optical properties, radiative forcing, and energy forcing (EF) from individual flights can be 2 orders of magnitude larger than the fleet-average values. Only 2.2% [2.0, 2.5%] of flights contribute to 80% of the contrail EF in this region. A small-scale strategy of selectively diverting 1.7% of the fleet could reduce the contrail EF by up to 59.3% [52.4, 65.6%], with only a 0.014% [0.010, 0.017%] increase in total fuel consumption and CO2 emissions. A low-risk strategy of diverting flights only if there is no fuel penalty, thereby avoiding additional long-lived CO2 emissions, would reduce contrail EF by 20.0% [17.4, 23.0%]. In the longer term, widespread use of new engine combustor technology, which reduces BC particle emissions, could achieve a 68.8% [45.2, 82.1%] reduction in the contrail EF. A combination of both interventions could reduce the contrail EF by 91.8% [88.6, 95.8%].
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