Limiting Black Soot and Ozone – Buying Time against Climate Change

According to the journal Nature Geosciences, “increasing concentrations of black carbon have substantially contributed to rapid Arctic warming during the past three decades.”

A paper from that journal, “Climate response to regional radiative forcing during the twentieth century,” was authored by climate researchers Drew Shindell, at the NASA Goddard Institute for Space Studies, and Greg Faluvegi of Columbia University. Shindell, Faluvegi, and many other climate scientists believe that limiting black carbon sources may “buy the world some time” in the race to control climate change as richer nations develop their climate change policies and begin taking the slow steps towards overhauling their carbon heavy energy sources.

The researchers assert that aerosols are responsible for “half or more” of Arctic warming. Unexpectedly, their paper’s claims and recommendations sparked a flurry of critical emails, perhaps due to confusion over the atmospheric roles of different aerosols.

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What are aerosols?

Aerosols are tiny particles suspended in the air (or any gas) and which act as “seeds” to form clouds. These aerosols come from natural sources (such as volcanoes and dust storms) and from human activity (such as burning of fossil fuels and agricultural over-use of land). Without aerosols, clouds could not form. The effect that aerosols have on the earth’s atmosphere depend on their size and concentration. If an aerosol (not to be confused with the aerosols in hairspray used to control the spread of the spray) is too small in size and concentration then more sunlight passes through to the Earth’s surface. Some aerosols (like darker particles from soot) also absorb sunlight as opposed to reflecting it back into space.

Most aerosols–natural and anthropogenic–actually have a cooling effect on the upper atmosphere (through blocking of sunlight). For example, consider volcanic ash, which, as of the end of the 20th Century (a volcanically active period), caused an estimated 5 - 7% decrease in sunlight reaching the Earth’s surface annually. Sulphate aerosols, which come from coal burning power plants, also have a cooling effect due to their attracting and trapping of free electrons.

But black soot and tropospheric ozone (ozone originating near the ground from industry verses the naturally, forming high altitude form) are the two most important aerosols studied in the paper. These two aerosols–the first a by-product of coal burning, the second being a smog-related compound– have the opposite effect, and actually increase atmospheric warming (by absorbing solar radiation). The good news is that these aerosols are fairly short-lived (their time suspended in the atmosphere is shorter) and by limiting their use and reducing their total output, we can make substantial, short-term progress in mitigating warming climate effects.

Comparatively, CO2 (which contributes to over 75% of greenhouse gas emissions), can remain in the atmosphere for thousands of years, while shorter-term pollutants like black soot, tropospheric ozone, and methane (an actual greenhouse gas, which also destroys protective ozone) have shorter “life spans”: Black carbon remains airborne for only a few weeks, and methane remains for no more than fifteen years.

According to the research paper, from 1976 to 2007, the average arctic surface temperature change was + 1.48 degrees C.  Of this rise, 1.09 degrees C. was due to black carbon aerosols (soot). Arctic warming is believed to be behind the recent breaking up of the Arctic ice sheet.

About 10% of the total aerosol pollution in our atmosphere comes from human activity.

In a speech in early last April, U.S. Secretary of State Hillary Clinton, acknowledging both the urgency of making real gains and the appeal of buying some time on climate change, stated: “Because they [aerosols] are short-lived, they also give us an opportunity to make rapid progress if we work to limit them.”

The biggest challenge here: while more developed countries produce a good amount of the total black carbon emissions, much of the daily generation of black soot comes from developing nations (like China and India, and Eastern Europe) using coal and/or wood burning stoves and chimneys. For most of these people, coal and/or wood burning are the only viable options they have to meet their energy and survival needs. Getting them to adopt alternative means (or more efficient ones) of cooking their food and heating their homes is a daunting enterprise. Part of the challenge is that richer nations are asking poorer ones to reduce their production of these aerosols, when such nations are still trying to develop their own climate policies (and are the major contributors to climate change inducing emissions). These policies are often viewed with skepticism and criticism by developing nations. This feeds into the emerging debate over what is known as ‘Climate Fairness” and/or “Climate Debt”. Necessarily, many experts and advisory NGOs in the Climate Change policy field are proposing incentive and investment programs. Such would be the function of the recently proposed Global Climate Fund, which grew out of the UN’s 2008 Framework Convention on Climate Change.

Photo Credit: ‘Local bread’ (Marrakesh, Morocco) by Wrote via Flickr

Aerosol diagrams and pie chart: NASA Earth Observatory

Corresponding author, email: Drew.T.Shindell@nasa.gov

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