Comments due by Dec. 10, 2017
SWEDEN’S parliament passed a law in June which obliges the
country to have “no net emissions” of greenhouse gases into the atmosphere by
2045. The clue is in the wording. This does not mean that three decades from
now Swedes must emit no planet-heating substances; even if all their
electricity came from renewables and they only drove Teslas, they would
presumably still want to fly in aeroplanes, or use cement and fertiliser, the
making of which releases plenty of carbon dioxide. Indeed, the law only
requires gross emissions to drop by 85% compared with 1990 12/3/2017 Greenhouse
gases must be scrubbed from the air.
But it demands that
remaining carbon sources are offset with new carbon sinks. In other words
greenhouse gases will need to be extracted from the air. Sweden’s pledge is
among the world’s most ambitious. But if the global temperature is to have a
good chance of not rising more than 2ºC above its pre-industrial level, as
stipulated in the Paris climate agreement of 2015, worldwide emissions must
similarly hit “net zero” no later than 2090. After that, emissions must go “net
negative”, with more carbon removed from the stock than is emitted.
This is because what matters to the climate is the total
amount of carbon dioxide in the atmosphere. To keep the temperature below a
certain level means keeping within a certain “carbon budget”—allowing only so
much to accumulate, and no more. Once you have spent that budget, you have to
balance all new emissions with removals. If you overspend it, the fact that the
world takes time to warm up means you have a brief opportunity to put things
right by taking out more than you are putting in (see chart 1). Being able to
remove carbon dioxide from the atmosphere is, therefore, a crucial element in
meeting climate targets. Of the 116 models the Intergovernmental Panel on
Climate Change (IPCC) looks at to chart the economically optimal paths to the
Paris goal, 101 assume “negative emissions”. No scenarios are at all likely to
keep warming under 1.5ºC without greenhouse-gas removal. “It is built into the
assumptions of the Paris agreement,” says Gideon Henderson of Oxford
University.
Climate scientists like Mr. Henderson have been discussing
negative-emissions technologies (NETs) with economists and policy wonks since
the 1990s. Their debate has turned livelier since the Paris agreement, the
phrasing of which strongly suggests that countries will need to invent new
sinks as well as cutting emissions. But so far politicians have largely ignored
the issue, preferring to focus on curbing current flows of greenhouse gases
into the atmosphere. NETs were conspicuous by their absence from the agenda of
the annual UN climate jamboree which ended in Bonn on November 17th. In the
short term this makes sense. The marginal cost of reducing emissions is
currently far lower than the marginal cost of taking carbon dioxide straight
from the atmosphere. But climate is not a short-term game. And in the long
term, ignoring the need for negative emissions is complacent at best. The
eventual undertaking, after all, will be gargantuan. The median IPCC model
assumes sucking up a total of 810bn tonnes of carbon dioxide by 2100,
equivalent to roughly 20 years of global emissions at the current rate. To have
any hope of doing so, preparations for large-scale extraction ought to begin in
the 2020s. Modellers favour NETs that use plants because they are a tried and
true technology. Reforesting logged areas or “afforesting” previously treeless
ones presents no great technical challenges. More controversially, they also
tend to invoke “bioenergy with carbon capture and storage” (BECCS). In BECCS,
power stations fuelled by crops that can be burned to make energy have their
carbon-dioxide emissions injected into deep geological strata, rather than
released into the atmosphere. The technology for doing the CCS part of BECCS
has been around for a while; some scenarios for future energy generation rely
heavily on it. But so far there are only 17 CCS programmes big enough to
dispose of around 1m tonnes of carbon dioxide a year. Promoting CCS is an
uphill struggle, mainly because it doubles the cost of energy from the dirty
power plants whose flues it scrubs. Other forms of low emission electricity are
much cheaper. Affixed to bioenergy generation, though, CCS does something that
other forms of generation cannot. The carbon which the plants that serve as
fuel originally took from the atmosphere above is sent into the rocks below,
making it a negative emitter. The problem with afforestation and BECCS is that
the plants involved need a huge amount of land. The area estimated ranges from
3.2m square kilometres (roughly the size of India) to as much as 9.7m square
kilometres (roughly the size of Canada). That is the equivalent of between 23%
and 68% of the world’s arable land. It may be that future agricultural yields
can be increased so dramatically that, even in a world with at least 2bn more
mouths to feed, the area of its farms could be halved, and that the farmers
involved might be happy with this turn of events. But it seems highly
unlikely—and blithely assuming it can be done is plainly reckless. Negative
thinking Less land-intensive alternatives exist—at least on paper. Some are low
tech, like stimulating the soil to store more carbon by limiting or halting
deep-ploughing. Others are less so, such as contraptions to seize carbon
dioxide directly from the air, or methods that accelerate the natural
weathering processes by which minerals in the Earth’s crust bind atmospheric carbon
over aeons or that introduce alkaline compounds into the sea to make it absorb
more carbon dioxide. According to Jennifer Wilcox of the Colorado School of
Mines, and her colleagues, the technology with the second-highest theoretical
potential, after BECCS, is direct air capture (see chart 2). This uses CCS-like
technology on the open air, rather than on exhaust gases. The problem is that
the concentration of carbon dioxide in the air, while very high by historical
standards, is very low by chemical-engineering ones: just 0.04%, as opposed to
the 10% or more offered by power-plant chimneys and industrial processes such
as cement-making. The technologies that exist today, under development by
companies such as Global Thermostat in America, Carbon Engineering in Canada or
Climeworks of Switzerland, remain pricey. In 2011 a review by the American
Physical Society to which Ms Wilcox contributed put extraction costs above $600
per tonne, compared with an average estimate of $60-250 for BECCS. Enhanced
weathering is at an even earlier stage of development and costs are still
harder to assess. Estimates range from $25 per tonne of carbon dioxide to $600.
On average, 2-4 tonnes of silicate minerals (olivine, sometimes used in Finnish
saunas because it withstands repeated heating and cooling, is a favourite) are
needed for every tonne removed. To extract 5bn tonnes of carbon dioxide a year
may require up to 20bn tonnes of minerals that must be ground into fine dust.
Grinding is energy-intensive. Distributing the powder evenly, on land or sea,
would be a logistical challenge to put it mildly. Ideas abound on a small
scale, in labs or in researchers’ heads, but the bigger mechanical schemes in
existence today capture a paltry 40m tonnes of carbon dioxide a year. Most
involve CCS and have prevented more carbon dioxide escaping into the atmosphere
from fossil-burning power plants, rather than removing it. Removing 8bn-10bn
tonnes by 2050, as the more sanguine scenarios envisage, let alone the
35bn-40bn tonnes in more pessimistic ones, will be a vast undertaking. Progress
will be needed on many fronts. All the more reason to test lots of
technologies. For the time being even researchers with a horse in the race are
unwilling to bet on a winner. Pete Smith of Aberdeen University speaks for many
NETs experts when he says that “none is a silver bullet, and none has a fatal
flaw.” It will also not come cheap. WITCH, constructed by Massimo Tavoni of
Politecnico di Milano, is a model which analyses climate scenarios. Unlike most
simulations, it also estimates how much research-and-development funding is
necessary to achieve roll-out at the sort of scale these models forecast. For
all low-carbon technologies, it puts the figure at $65bn a year until 2050,
four times the sum that renewables, batteries and the like attract today. Mr.
Tavoni says a chunk of that would obviously need to go to NETs, which currently
get next to nothing. Even the less speculative technologies need investment
right away. Trees take decades to reach their carbon-sucking potential, so
large-scale planting needs to start soon, notes Tim Searchinger of Princeton
University. Direct air capture in particular looks expensive. Boosters note
that a few years ago so did renewables. Before technological progress brought
prices down, many countries subsidised renewable-energy sources to the tune of
$500 per tonne of carbon dioxide avoided and often spent huge sums on it.
Christoph Gebald, co-founder of Climeworks, says that “the first data point on
our technological learning curve” is $600, at the lower end of previous
estimates. But like the price of solar panels, he expects his costs to drop in
the coming years, perhaps to as low as $100 per tonne. However, the falling
price of solar panels was a result of surging production volumes, which NETs
will struggle to replicate. As Oliver Geden of the German Institute of
International and Security Affairs observes, “You cannot tell the greengrowth
story with negative emissions.” A market exists for rooftop solar panels and
electric vehicles; one for removing an invisible gas from the air to avert
disaster decades from now does not. Much of the gas captured by Climeworks and
other pure NETs firms (as opposed to fossil-fuel CCS) is sold to makers of
fizzy drinks or greenhouses to help plants grow. It is hard to imagine that
market growing far beyond today’s total of 10m tonnes. And in neither case is
the gas stored indefinitely. It is either burped out by consumers of carbonated
drinks or otherwise exuded by eaters of greenhouse grown produce. There may be
other markets, though. It is very hard to imagine aircraft operating without
liquid fuels. One way to provide them would be to create them chemically using
carbon dioxide taken from the atmosphere. It is conceivable that this might be
cheaper than alternatives, such as biofuels— especially if the full
environmental impact of the biofuels is accounted for. The demand for direct
air capture spurred by such a market might drive its costs low enough to make
it a more plausible NET. From thin air One way to create a market for NETs
would be for governments to put a price on carbon. Where they have done so, the
technologies have been adopted. Take Norway, which in 1991 told oil firms
drilling in the North Sea to capture carbon dioxide from their operations or
pay up. This cost is now around $50 per tonne emitted; in one field, called
Sleipner, the firms have found ways to pump it back underground for less than
that. A broader carbon price—either a tax or tradable emissions permits—would
promote negative emissions elsewhere, too. Then there is the issue of who
should foot the bill. Many high-impact negative emissions schemes make most
sense in low-emitting countries, says Ms Wilcox. Brazil could in theory
reforest the cerrado (though that would face resistance because of the region’s
role in growing soyabeans and beef). Countries of sub Saharan Africa could do
the same in their own tropical savannahs. Spreading olivine in the Amazon and
Congo riverbasins could soak up 2bn tonnes of carbon dioxide. Developing
countries would be understandably loth to bankroll any of this to tackle
cumulative emissions, most of which come from the rich world. The latter would
doubtless recoil at footing the bill, preferring to concentrate on curbing
current emissions in the mistaken belief that once these reach zero, the job is
done. Whether NETs deserve to be lumped in with more outlandish
“geoengineering” proposals, such as cooling the Earth with sunlight-reflecting
sulphur particles in the stratosphere, is much debated. What they have in
common is that they offer ways to deal with the effects of emissions that have
already taken place. Proponents of small-scale, low-impact NETs, such as
changes to soil management on farms, though, bridle at being considered
alongside what they see as high-tech hubris of the most disturbing kind. NETs
certainly inspire fewer fears of catastrophic, planetary-scale side-effects
than “solar radiation management”. But they do stoke some when it comes to the
consequences of tinkering with the ocean’s alkalinity or injecting large
amounts of gas underground. And the direct effects of large-scale BECCS or
afforestation projects would be huge. If they don’t take up arable land, they
need to take up pasture or wilderness. Either option would be a big deal in
terms of both human amenity and biodiversity. Another concern is the impact on
politicians and the dangers of moral hazard. NETs allow politicians to go easy
on emission cuts now in the hope that a quick fix will appear in the future.
This could prove costly if the technology works—and costlier still if it does
not. One study found that following a 2°C mitigation path which takes for
granted NETs that fail to materialise would leave the world closer to 3°C
warmer. Mr Geden is not alone in fearing that models that increasingly rely on
NETs are “a cover for political inaction”. Academics are paying more attention.
This year’s edition of “Emissions Gap”, an influential annual report from the
UN Environment Programme, devotes a chapter to carbon-dioxide removal. Mr
Henderson is leading a study of the subject for Britain’s Royal Society;
America’s National Academy of Sciences has commissioned one, too. Both are due
next spring. The IPCC will look at the technology in its special report on the
1.5ºC target, due next autumn. There’s some money, too. Cagineering has attracted
backers such as Bill Gates, and now has a pilot plant in Canada. Climeworks has
actually sold some carbon-offset credits—to a private investor and a big
corporation—on the basis of the carbon dioxide it has squirrelled away at a
demonstration plant it recently launched in Iceland. Earlier this year
Britain’s government became the first to set aside some cash specifically for
NETs research. In October America’s Department of Energy announced a series of
grants for “novel and enabling” carbon-capture technologies, some of which
could help in the development of schemes for direct air capture. Richard
Branson, a British tycoon, has offered $25m to whoever first comes up with a
“commercially viable design” that would remove 1bn tonnes of greenhouse gases a
year for ten years. All this is welcome, but not enough. The sums involved are
trifling: £8.6m ($11.3m) in Britain and $26m from the Department of Energy. The
offset sold by Climeworks was for just 100 tonnes. Mr Branson’s prize has gone
unclaimed for a decade. A carbon price—which is a good idea for other reasons,
too, would beef up interest in NETs. But one high enough to encourage pricey
moonshots may prove too onerous for the rest of the economy. Any price would
promote more established low-carbon technologies first and NETs only much
later, thinks Glen Peters of the Centre for International Climate Research in
Oslo.Encouraging CCS for fossil fuels as a stepping stone to NETs appeals to
some. The fossil-fuel industry says it is committed to the technology. Total, a
French oil giant, has promised to spend a tenth of its $600m research budget on
CCS and related technologies. A group of oil majors says it will spend up to
$500m on similar projects between now and 2027. But the field’s slow progress
to date hardly encourages optimism. Governments’ commitment to CCS has
historically proved fickle. Last year Britain abruptly scrapped a £1bn public
grant for an industrial-scale CCS plant which would have helped fine-tune the
technology. For this to change, politicians must expand the focus of the
23-year-old UN Framework Convention on Climate Change from cutting emissions of
greenhouse gases to controlling their airborne concentrations, suggests Janos
Pasztor, a former climate adviser to the UN secretary-general. In other words,
they must think about stocks of carbon dioxide, not just flows. This is all the
more true because emissions continue to elude control. After three years of
more or less stable emissions, a zippier world economy looks on track to belch
2% more carbon dioxide this year. That amounts once again to borrowing more of
the planet’s remaining carbon budget against future removal. It doesn’t take a
numerate modeller like Mr Tavoni to grasp that, in his words, “If you create a
debt, you must repay it.”
