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change, but how is that going to look on the
ground?” he asks.
In 2015, the Paris climate agreement es-
tablished a goal of limiting global warm-
ing to “well below” 2°C. In the most recent
report of the Intergovernmental Panel on
Climate Change, researchers surveyed
possible road maps for reaching that goal
and found something unsettling. In most
model scenarios, simply cutting emissions
isn’t enough. To limit warming, human-
ity also needs negative emissions tech-
nologies (NETs) that, by the end of the
century, would remove more CO2 from the
atmosphere than humans emit. The tech-
nologies would buy time for society to rein
in carbon emissions, says Naomi Vaughan,
a climate change scientist at the University
of East Anglia in Norwich, U.K. “They al-
low you to emit more CO2 and take it back
at a later date.”
Whether that’s doable is another ques-
tion. Some NETs amount to giant air-
purifying machines, and many remain
more fiction than fact. Few operate at com-
mercial scales today, and some researchers
fear they offer policymakers a dangerous
excuse to drag their feet on climate action
in the hopes that future inventions will
clean up the mess. “In many ways, we’re
saying we expect a bit of magic to occur,”
says Chris Field, a climate scientist at
Stanford University in Palo Alto, Califor-
nia, who instead favors drastic emissions
reductions. Others say we no longer have
a choice—that we have dallied too long to
meet the Paris targets solely by tighten-
ing our belts. “We probably need aggres-
sive and immediate mitigation, plus some
negative emissions,” says Pete Smith, a soil
scientist and bioenergy expert at the Uni-
versity of Aberdeen in the United Kingdom.
One particular technology has quietly
risen to prominence—thanks to global
models—and it is the one on tap in Bozeman. The idea is to cultivate fast-growing
grasses and trees to suck CO2 out of the
atmosphere and then burn them at power
plants to generate energy. But instead of
being released back into the atmosphere
in the exhaust, the crops’ carbon would
be captured and pumped underground.
The technique is known as bioenergy with
carbon capture and storage, or—among
climate wonks—simply as BECCS.
Few at the Bozeman meeting have heard
of BECCS, and most are suspicious; it
sounds like a far-fetched scheme that might
disrupt the world as they know it. During a break, Martha Kauffman, a regional
director for the World Wildlife Fund in
Bozeman, wonders whether BECCS might
encroach on lands used to graze cattle. In
grasslands like this, she says, “It’s the pri-
1980 2000 2020 2040 2060 2080 2100
fossil fuels, industry,
and net land-use change
Six ways to pull CO2 out of the air
Take it back
Researchers are pursuing a handful of negative emissions technologies (NE Ts) that would mitigate global
warming by pulling carbon dioxide (CO2) out of the atmosphere. A prominent NET is bioenergy with carbon
capture and storage (BECCS), because it combines existing technologies.
Fast-growing plants are harvested
and burned to make energy.
Exhaust carbon is captured and
Planted trees capture CO2 as
they grow. The carbon remains
sequestered as long as forests
are not cut down.
When spread across fields or
beaches and wetted, crushed
silicate minerals like
olivine naturally absorb CO2.
Direct air capture
CO2 in air selectively “sticks”
to chemicals in filters. Filters are
reused after releasing pure CO2,
which can be stored underground.
Injections of nutrients like iron
spur phytoplankton blooms, which
absorb CO2. When they die,
they take the carbon to the sea floor.
A global unwinding
In order to prevent the world from warming more than 2°C, models count on the fast development
of NETs. But many scientists question whether they can be scaled up in time.
*Median values at 10-year time steps of 18 scenarios evaluated by six models using shared socioeconomic pathways
assessed in the next report of the Intergovernmental Panel on Climate Change.
Biochar and soil sequestration
Charring biomass stores carbon
in soil by making it resistant to
decomposition. Altered tilling
practices also enhance CO2 storage.
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