HOT TOPIC

CLIMATE’S SMOKY SPECTRE

With their focus on greenhouse gases, atmospheric scientists have largely

overlooked lowly soot particles. But black carbon is now a hot topic among

researchers and politicians.

“Sea ice may be

melting anyway, but

black carbon can

cause more melting

and earlier melting.”

— Andreas Stohl

Some Indian cooking

methods are contributing

to atmospheric soot levels.

Stopping the soot

Last month the eight-nation

Arctic Council appointed a

task force to look at ways to

reduce black carbon and other

key pollutants responsible

for rapid Arctic warming. It

was a sign that the scientists

pushing the link between

black carbon and climate

(see main article) are getting

their message through to

governments. The question

faced by the council, and by

policy-makers across the

world, is what to do.

Black carbon, a primary

component of soot, is a

ubiquitous product of

incomplete combustion,

formed by natural forest fires,

motor vehicles, coal plants

and myriad other sources.

Soot contains both black

carbon and light-coloured

particles that cool the planet;

smoke produced by sources

such as cooking stoves and

diesel engines tends to be rich

in darker particles. Reducing

black-carbon emissions isn’t a

technical problem — modern

stoves and filters can do most

of the work — so much as

an issue of governance and

resources.

“Black carbon is perhaps

the biggest, fastest bite we

can take out of the climate

problem,” says Durwood

Zaelke, who heads the

Institute for Governance and

Sustainable Development

in Washington DC and

has helped spearhead the

movement internationally. “It

needs, however, to be followed

with aggressive regulatory

action.”

Global soot emissions have

been rising steadily since

the mid-1800s, although in

recent decades the source of

emissions has shifted from

industrialized to developing

nations. Pinning down actual

emissions is difficult, but Tami

Bond, a researcher at the

University of Illinois, Urbana–

Champaign, estimates that

diesel combustion and

residential fuel use (from coal,

wood and agricultural debris)

each produce roughly onequarter

of the total; another

40% comes from wildfires and

controlled agricultural burning;

various industrial sources

make up the remainder.

Industrialized nations could

clean up fossil fuels further

and reduce agricultural

emissions at home. But

much of the focus will be on

developing countries. The

hope there is that current

concerns over climate change

will energize existing efforts

to clean up diesel emissions

and replace inefficient cooking

stoves.

The precedent is there.

China delivered roughly 150

million stoves to rural areas

in the 1980s and early 1990s

in an effort to reduce fuel use,

says Kirk Smith, a rural energy

expert at the University

of California, Berkeley.

Smith is working with local

communities to encourage

the use of locally produced,

clean-burning biomass stoves,

which reduce emissions of

carbon dioxide, methane and

other dangerous compounds.

The impetus for the work has

been to improve public health

and reduce greenhousegas

emissions, but the new

attention on black carbon

doesn’t hurt, says Smith.

“It’s sort of the pollutant of

the month and you need to

take advantage of what’s on

people’s minds.”