24 Scientific American, October 2019
VENTURES
THE BUSINESS OF INNOVATION
Wade Roush is the host and producer of Soonish, a podcast
about technology, culture, curiosity and the future. He
is a co-founder of the podcast collective Hub & Spoke and
a freelance reporter for print, online and radio outlets,
such as MIT Technology Review, Xconomy, WBUR and WHYY.Low-Carbon Air
Travel Is Coming
Buy offsets if you want, but for real hope,
look to electric planes
By Wade Roush
Back in 2015, I got pretty serious about reducing or offsetting
my carbon footprint. I don’t have kids, I don’t own a car and
I don’t eat meat, so I already had three of the biggies covered. To
make up for my electricity use, I started buying credits from a
nonprofit that funds wind turbines and other renewable energy
projects in New England. Then it was time to examine my hab-
it of boarding kerosene-fueled jet aircraft.
An online calculator showed that the flights I take every year
put a yikes-inducing 15 metric tons of carbon into the atmo-
sphere—equivalent to the overall annual carbon emissions of
three average earthlings. So I signed up with a company called ter-
rapass to buy offsets for 12 tons of carbon a year, at about $10 per
month. Terrapass uses that money to do commendable things
such as capturing methane from landfills, building wind farms
and preserving carbon-sequestering forests.
I’m not under the illusion that these projects cleanse my sins
as an air traveler. At best, they simply prevent the release of an
equal quantity of greenhouse gases down the road. The offsets do
help me and other consumers feel less guilty about flying—which
is probably why airlines such as United and Delta now offer them
as part of the booking process. And on a larger scale, there’s evi-
dence that offsets function as a kind of self-imposed carbon tax,
encouraging people who buy them to keep their own energy use
in check. But the reality is that voluntary offsets will never come
close to matching aviation emissions, which account for 2 percent
of overall human-induced carbon emissions.
For one thing, any benefit from offsets is likely to be over-
whelmed by growing demand for air travel. According to a recent
report from Airbus, about 40 percent of the world population is
now middle class, and by 2037 this group will have mushroomed
to more than 50 percent, or some five billion people—“all in the
pool of regular or potential new” passengers.
And buying an offset isn’t a guarantee that your flight emis-
sions will actually be, you know, offset, since it’s difficult to prove
that carbon-avoidance projects wouldn’t have happened anyway
or that the neutralized carbon will never be released in the future.
And critics say offsets can be an excuse for inaction. Australian
engineer and author Sharon Beder has called them “a greenwash-
ing mechanism that enables individuals to buy themselves green
credentials without actually changing their consumption habits.”
Regardless of their relation to consumer trends, offsets aren’t
a solution to the underlying physics problem in aviation, which is
that today’s long-haul passenger jets can’t take off without burn-
ing a high-energy-content fuel such as kerosene. That’s why OPEC
is confident that worldwide demand for jet fuel will reach nine
million barrels a day by 2040, up from 6.3 million in 2017.
Short of drastic rationing of air travel, the only long-term solu-
tion for aviation’s carbon woes is electrification. Biofuels from
feedstocks such as sugarcane, algae and household garbage,
which burn more cleanly than fossil fuels, could help in the short
run—United has been mixing them into traditional jet fuel since- But the real hope lies in projects such as E-Fan X, a test
plane from Airbus, Rolls-Royce and Siemens in which one of the
four gas-powered turbofans is replaced by an electric motor. The
partners see the project as a step toward meeting the European
Union’s ambitious “Flightpath 2050” goal of reducing aviation’s
carbon dioxide emissions by 75 percent by 2050.
Start-ups are getting into the game, too: Seattle’s Zunum
Aero, backed by Boeing and JetBlue, is designing a regional jet
with batteries in the wings and fans powered with a “hybrid to
electric” power train. To be light enough for flight, aviation bat-
teries will need a specific energy—a measure of how much pow-
er a battery contains for its weight—far beyond that of today’s
lithium-ion battery packs. So, for the time being, Zunum’s pow-
er train will run partly on jet fuel.
The improvements in batteries and motors needed to fully
electrify the skies could take “the next few decades,” Zunum co-
founder B. Matthew Knapp acknowledged in a recent Nature
Sustainability op-ed. Meanwhile buying offsets is a substitute
that both feels good and does good. Just don’t assume that it will
keep our climate-spoiling travel habits aloft forever.
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