Reducing emissions of black carbon soot and ground-level ozone would quickly make a considerable dent in the climate change problem and would also contribute to public health and protect crop yields, according to an essay in the September/October issue of Foreign Affairs.

The piece was co-authored by Scripps Institution of Oceanography at UC San Diego climate and atmospheric scientist V. Ramanathan and Jessica Seddon Wallack, director of the Center for Development Finance at the Institute for Financial Management and Research in Chennai, India.

Right now the world is looking at well over a 2 degree rise in temperatures from the pre-industrial age. To avoid the severe consequences associated with such a dramatic change, we need to look at other feasible complementary measures, in addition to reducing CO₂ emissions, that will provide near-term mitigation. -V. Ramanathan

Ramanathan concludes that full implementation of existing emissions-control technologies could offset the warming effects of one to two decades of carbon dioxide emissions.

A dedicated effort would not only allow more time for creation of effective carbon dioxide-reduction regulations but would also have enormous public health and economic benefits, the authors said.

Black carbon is produced largely by diesel vehicles and the burning of biomass, including in cookstoves in developing countries like China and India. It contributes to 7% of child deaths worldwide that result from fatal respiratory infections. Black carbon is also responsible for almost 50% of warming in the Arctic as well as extensive snow and ice melt in the Himalayas. Available technology such as diesel particulate filters for vehicles and cleaner- burning biomass and solar cookstoves can significantly reduce black carbon emissions.

Focusing on reducing emissions of black carbon and ozone precursors is the low-hanging fruit: the implementation is feasible, and the benefits would be numerous and immediate. -Wallack and Ramanathan

Ground level or tropospheric ozone (different than the stratospheric ozone that blocks the sun’s UV rays) is formed by ozone precursor gases such as carbon monoxide, nitrogen oxides, methane, and other hydrocarbons. Improving the efficiency of industrial and transportation combustion processes can reduce these gases. Besides a danger to breathe, ozone lowers crop yields. A recent study reported that ozone’s damage to crop yields in 2000 resulted in an economic loss of $14-26 billion annually.  

Both black carbon particles and ozone gas remain in the atmosphere for periods of only weeks to months, as opposed to the centuries that carbon dioxide remains in the atmosphere. The authors argue that mitigation measures targeting black carbon and ozone would therefore produce immediate climate benefits.

Additionally it would help alleviate damage to respiratory health in humans caused by black carbon smog, the fourth-leading cause of premature death in developing countries. Crop yields would be aided by ozone-removal efforts since the gas damages plant cells and disrupts chlorophyll production.

Wallack and Ramanathan further point out that technologies to reduce black carbon and ozone already exist. The authors cite a finding from an American non-profit research organization that shows that retrofitting one million tractor-trailers with diesel particulate filters would produce effects equal to removing 5.7 million cars from the road.

The main challenges, according to the authors, lie in motivating adoption of technologies to reduce diesel emissions and making technologies to burn biomass fuels more efficiently accessible around the world. These are more akin to development challenges than traditional environmental policies.

Ramanathan said that these mitigation measures could serve to hedge against the full effects of global warming caused by greenhouse gases. They will also offset the acceleration of global warming that can occur when the atmosphere is cleaned of reflective particles such as sulfates from coal combustion that have an atmospheric cooling effect.

Our finding provides a tremendous incentive to help the over 3 billion people who live on less than $2 a day and are forced to cook and heat their homes with biomass fuels such as dung, crop residues and firewood. -V. Ramanathan

Diesel exhaust and cooking with biomass fuels both have net warming effects, though the magnitude of biomass burning’s warming effect is not well understood. Ramanathan is currently studying the net warming effect of biomass burning as part of Project Surya, an effort to measure the effect of replacing traditional cooking methods in rural India with cleaner-burning alternatives. Wallack and UCSD Rady School of Business Professor Vish Krishnan are also participating in Project Surya to identify ways to remove bottlenecks to larger-scale adoption of technologies for cleaner burning of renewables.

US Senators Tom Carper (D-DE), Jim Inhofe (R-OK), Barbara Boxer (D-CA) and John Kerry (D-MA) introduced a black carbon bill earlier this year, as did Congressmen Jay Inslee (D-WA), Peter Welch (D-VT), and Mike Honda (D-CA). A provision on black carbon is also included in the Waxman-Markey climate bill.

The full article by Jessica Seddon Wallack and Veerabhadran Ramanathan (2009) The Other Climate Changers: Why Black Carbon and Ozone Also Matter is available in Foreign Affairs September/October 2009