And that could be achieved in addition to climate mitigation through reduced emissions of greenhouse gases.

A few days ago there was a forecast in Nature Climate Change that stated -under business as usual industrial climate forcing- we risk to lose (more than) 84 percent of the world’s biodiversity by 2080 – a much faster decline than any previous estimate had come up with.

In order to keep spirits up we promised to find some compensating good news – and what’s better than challenging the business as usual scenario to begin with?

Yesterday Mark Jacobson of Stanford University did just that during his presentation at the American Chemical Society.

Like many before him Jacobson argues the role of soot – or ‘black carbon’ – is being ignored in the international efforts to combat climate change. After CO2 soot is the most important contributor to global warming, not because it would be a greenhouse gas [soot particles after all are solid], but because soot lowers the Earth’s albedo, transforming solar radiation to heat radiation.

Soot aerosols even decrease the albedo of ‘space’ as it also absorbs a portion of the solar radiation that was already reflected by Earth’s surface, capturing the energy in midair just before it could escape and thereby creating more heat, further warming the atmosphere.

Soot’s importance is its potential

What’s new to Jacobson’s story is firstly his call to action. He states through aggressive anti-soot policy, by combined targeting of all sources from exhaust filters for vehicles to cooking stoves to replace wood fires in poor nations, ‘within 5-10 years’ worldwide soot emissions could be reduced by 90 percent.

The benefits of this are also somewhat larger than previously thought. Jacobson says his calculations show an additional reason why soot is ‘bad for the climate’: soot particles disturb an even cloud cover, thereby further reducing the Earth’s general albedo.

All in all soot would be responsible for 17 percent of the anthropogenic climate forcing, making it more important than for instance methane.

Another benefit of anti-soot policy is soot’s short atmospheric lifespan. The carbon aerosols usually remain airborne for no longer than days or weeks. This means soot mitigation could translate to immediate cooling – whereas CO2 reductions only help slow down warming, because CO2 molecules remain in the atmosphere for decades, centuries or perhaps even longer.

Arctic needs fresh layer of snow – Earth more sulphur

Once settled though soot has a last trick up its sleeve: glacier darkening. Especially in arid cold climates industrial soot pollution can lead to darker snow and ice and faster melting under the influence of sunshine. If however we succeed in clamping down on soot emissions, one fresh layer of snow would solve this problem too.

Jacobson’s hoped industrial policy should [if climate were our only concern] focus on soot specifically though and not turn to indiscriminate aerosol emission reductions (as has happened in the West since the 70s and 80s). Because the Earth’s albedo may need the white sulphur pollution just as hard as it can miss the black carbon.

© Rolf Schuttenhelm | www.bitsofscience.org