Cut pollution and maybe, the planet will cool

Recent research suggests that if we can clean up diesel engines and inefficient cook stoves in India and China for example, that could delay the effects of greenhouse-gas buildup even if pollution from coal-fired power plants persists. The study concludes that if every country were to do what California has done in the last couple of decades to clean up diesel emissions, it would slow down global warming by 15 percent.

Aerosol pollutants such as sulfur dioxide, soot, and ozone are all bad for human health, but they have different effects on the climate. Some of the aerosols are warming the planet, and some are cooling the planet. For example, sulfates that form from coal-plant exhaust reflect sunlight back into space, acting to shade the planet and cool it off. Black-carbon particles from diesel exhaust, on the other hand, absorb sunlight and heat up, warming the atmosphere. Add them together, and on balance they could be cooling the planet! That is, they mask some of the temperature increase that would have occurred as a result of carbon dioxide emissions. But this effect would be more significant if the particulates that help heat up the atmosphere were removed.

What would happen if we immediately got rid of only the black-carbon aerosols? Doing that might lead to a cooling of the planet by half a degree to a degree Celsius. However the impact on temperature is hard to pin down. For one thing, pollution affects clouds and rainfall, which have complicated effects on climate. So it is not easy to assess.

Black carbon flows

Black carbon rears its head again! This time it breaks earlier notions of creating a carbon reserve in soil.

A smaller proportion of black carbon created during combustion will remain in soil than have been estimated before. Contrary to previous understanding, burying black carbon in the ground in order to restrain climate change will not create a permanent carbon reserve. Instead, a part of black carbon will dissolve from soil to rivers.

The burning of organic matter creates 40-250 million tons of black carbon every year. Black carbon is formed through the incomplete combustion of organic matter, e.g. in forest fires, slash-and-burn and controlled burning of fields. In the light of new research results, much discussed "bio-carbon" may not be that beneficial in terms of mitigating climate change. In any case, the stability of carbon in soil has been a central factor of bio-carbon applications.

By sampling rivers all around the world, the researchers estimated that the annual amount of black carbon flowing via rivers to the ocean is 27 million tons per year. For this project, water samples were collected from the ten largest rivers in the world. These rivers carry one third of fresh water running to oceans, and their catchment area covers 28% of the whole land area in the world. In addition to the samples used in the river project, the research published in Science was supplemented with samples from many other rivers all over the world. The total number of researched samples was 174.

Black carbon is 'black'!

Black carbon is the second largest man-made contributor to global warming and its influence on climate has been greatly underestimated, according to the first quantitative and comprehensive analysis of this issue. Black carbon has a much greater (twice the direct) climate impact than reported in previous assessments. Black carbon ranks “as the second most important individual climate-warming agent after carbon dioxide”. Cleaning up diesel engines and some wood and coal combustion could slow the warming immediately.

Published in the Journal of Geophysical Research-Atmospheres the study says the direct influence of black carbon, or soot, on warming the climate could be about twice previous estimates.  Accounting for all of the ways it can affect climate, black carbon is believed to have a warming effect of about 1.1 Watts per square meter (W/m²), approximately two thirds of the effect of the largest man made contributor to global warming, carbon dioxide. Co-lead author David Fahey from the U.S. National Oceanic and Atmospheric Administration (NOAA) said, “This study confirms and goes beyond other research that suggested black carbon has a strong warming effect on climate, just ahead of methane.”  The study, a four-year, 232-page effort, led by the International Global Atmospheric Chemistry  (IGAC) Project, is likely to guide research efforts, climate modeling, and policy for years to come.

The international team urges caution because the role of black carbon in climate change is complex.  “Black carbon influences climate in many ways, both directly and indirectly, and all of these effects must be considered jointly”, says co-lead author Sarah Doherty of the University of Washington, an expert in snow measurements. The dark particles absorb incoming and scattered heat from the sun (solar radiation); they can promote the formation of clouds that can have either cooling or warming impact; and black carbon can fall on the surface of snow and ice, promoting warming and increasing melting.  In addition, many sources of black carbon also emit other particles whose effects counteract black carbon, providing a cooling effect.

The study suggests mitigation of black carbon emissions for climate benefits must consider all emissions from each source and their complex influences on climate. Black carbon and its contribution to global warming has been a bone of contention between some academic groups with some believing that it is merely a hype to focus the spotlight on the poor nations where burning wood and charcoal could be seen as a major contributor!

Cut soot, save lives and cool the globe

An international team of scientists says that governments can significantly reduce global warming, and prevent millions of premature deaths, by targeting emissions of methane and soot. In a new study published in the journal Science, the researchers say simple strategies that target those emissions and use existing technologies could shave nearly 1 degree Fahrenheit off the warming projected by mid-century.

And with international efforts to reduce emissions of carbon dioxide, the main cause of climate change, largely stalled, it represents a cheaper and more attainable approach. Strategies to reduce methane emissions include improving methods of capturing gas from mines and oil- and gas-producing facilities and reducing leaks from pipelines and landfills; global levels of soot, or black carbon, can be cut by requiring more efficient filters for diesel vehicles, developing cleaner-burning cook stoves and imposing bans on burning agricultural land.

Such measures would prevent 700,000 to 4.7 million air pollution-related deaths per year, the study says. “Ultimately, we have to deal with CO2, but in the short term, dealing with these pollutants is more doable, and it brings fast benefits,” said Drew Shindell, the lead author and researcher at NASA’s Goddard Institute for Space Studies and Columbia University’s Earth Institute.

In developing and developed nations, burning wastes also adds to the soot. Particularly dry garbage. This will take time to change.

Removing the black carbon can help

Placing strict limits on a handful of common air pollutants could pay big dividends for efforts to limit climate change, improve public health and increase agricultural productivity, according to a new U.N. report. These are aerosols like black carbon, and methane and ozone. Additionally, limiting emissions of black carbon and chemicals that react with sunlight to form tropospheric ozone could prevent 2.4 million premature deaths and the loss of 1 to 4 percent of the global output of maize, rice, soybean and wheat each year, the analysis found.

Now that's a huge benefit to be ignored!

Cuts in these emissions could be made with existing technology, the report says, and would "have immediate and multiple benefits for human well-being." Possible strategies for reducing black carbon, methane and ozone include capturing methane produced by landfills and fossil fuel extraction, introducing cleaner-burning cookstoves, installing particulate filters on diesel engines and banning the practice of burning fields of agricultural waste.

Black carbon is produced by the burning of fossil fuels as well as biomass like wood and dung.

Researchers expanded the analysis to look at chemicals like methane and precursors to ozone because they are emitted by the same processes -- like biomass burning -- that produce black carbon. Like black carbon, methane and ozone are potent, even if short-lived, greenhouse gases. Black carbon, for example, lingers in the atmosphere for weeks, compared to CO2, which can last for centuries to millennia.

All three can damage human health, while ozone can lower crop yields. Meanwhile, black carbon acts in several ways to accelerate climate change. It absorbs heat from sunlight, warming the surrounding air. When particles of black carbon fall from the atmosphere on ice or snow, they hasten melting. Earlier work suggests that black carbon emissions caused half the total warming in the Arctic between 1890 and 2007.

Perhaps governments of developing nations will pay attention and do something fast about the burning of biomass in unhealthy, unhygienic cookstoves, etc.

Clouded verdict

A new analysis of satellite data, collected over a decade, has identified the concentration, distribution, and composition of aerosol pollution over the Indian subcontinent. Using the multi-angle imaging spectroradiometer (MISR) from NASA’s Terra spacecraft, researchers at the University of Illinois at Urbana-Champaign, were able to document high levels of natural and human-caused pollution and reveal unexpected seasonal shifts in pollution.

Aerosol pollution across much of the country was two to five times higher than World Health Organization standards, with levels fluctuating during the seasons as monsoon rains wash away much of the smog and particulate matter, according to the study published in the Journal of Geophysical Research.

Black carbon particles, commonly called soot, are dark and light-absorbing and therefore warm the climate. Soot comes from combustion of fossil and biofuels, especially burning of diesel, coal and wood. Due to its warming effects, reduction of soot could help cool climate. However, soot absorption also affects cloud distributions and the verdict on how the clouds change is unclear. Because clouds mostly cool the climate, the possibility that soot absorption could increase cloud cover needs to be considered. And that means reducing BC may not be the silver bullet solution many thought.

Global model studies of soot effects on clouds do indeed find a variety of cloud responses, with increased clouds in some regions and decreased clouds in others. Most of the global model studies indicate that the net cloud response to absorbing particles is cooling. This suggests the need for caution when pursuing mitigation of soot in order to cool climate.