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Black carbon: tackling crop-residue burning in South Asia

This post is an abridged version of an original article which appeared in Global Change magazine, the in-house magazine of the International Geosphere-Biosphere Programme (IGBP). The original article is available online.

Every year, during the dry season, a brownish haze envelops South Asia and its fringing seas. Reaching some three kilometres high, this atmospheric brown cloud is a cocktail of pollutant gases and particles. Black carbon is an important part of it. Produced mostly from human activities, black carbon warms the lower atmosphere and is the second most important contributor to global warming after carbon dioxide[1].

If we are looking for short-term wins in the fight against climate change then cutting back on activities that churn out this soot is an appealing idea. In Europe and the Americas this can most easily be done by tackling the diesel engine1. But in South Asia there’s an equally important source of soot –  biomass burning[2] – both for cooking and to rid farmers of tens of millions of metric tonnes of rice stalks after harvest.

But the burning of biomass doesn’t send just soot wafting up into the air: it also releases organic compounds that in fact cool the climate. In practice, the soot and the organic compounds tend to balance each other out and the process contributes little to global warming, at least in the short term[1].

Still, it makes sense to try and curb the problem – the unusually sooty brown cloud over and around South Asia is thought to be changing rainfall patterns and melting the Himalayan glaciers[3]. It brings chaos to flight timetables, surges in hospital admissions – and many deaths.[4]

How do you persuade farmers not to set their fields alight? It’s not as simple as confiscating their matches. Fine textured research into why they burn and what the alternatives are has now illuminated the situation, thanks to the South Asian Network for Development and Environmental Economics (SANDEE) in Nepal. The surveys were undertaken in parts of Pakistan, India, Nepal and Bangladesh [5],[6],[7],[8].

The farmers burn because they want to rid themselves of useless rice stalks as quickly and cheaply as possible, in time for planting wheat. Burning leaves a soil that is easy to plough in readiness for the next crop. The rice stalks might have been used for animal fodder instead but the need for this has diminished with the advent of the motorised tractor. Many farmers believe burning rids the land of weeds, pests and diseases and that the ash is good for the soil, which does seem to be the case in the short term. In the longer term, studies show it is far better to plough the residue back into the soil or compost it: but this is labour intensive and hence expensive.

Would a bit of extra money talk them out of it? Krishna Prasad Pant, of Kathmandu University in Nepal, recruited farmers from the country’s southern lowland Terai region. Using a “reverse auction”, he encouraged the farmers each to name their price – the minimum they would accept – to refrain from burning. The average bid was for $78 (USD) per hectare.

Pant’s team trained the farmers either to plough the stalks back into the soil (which meant hiring a bigger, more costly tractor) or to cut them by hand and compost them in a corner of the field (for which they needed to hire more labour). About 85% stuck to their agreement and did not burn that season: many, in a follow-up survey, requested a repeat of the intervention. Based on these results Pant thinks the government should pay farmers not to burn, alongside educating them on soil fertility and composting of residue. He is not convinced that other options are feasible: “Putting a legal ban is very difficult to do because it is their traditional right.”

Executive Director of SANDEE and member of the International Geosphere-Biosphere Programme (IGBP) Scientific Committee Priya Shyamsundar thinks subsidised new technologies might be a better option than paying farmers not to burn: “New technologies don’t need to be monitored across the board so it’s an easier solution, and regulations such as bans don’t always work well.”

Arguably, it was new technology that helped create the problem – the popular combine harvester leaves a longer-stalked residue than rice harvested the old way, by hand. But now there’s a new piece of technology that could resolve the problem: the Happy Seeder – a miraculous-seeming machine that cuts and lifts rice straw, sows the wheat seed, and deposits the straw on top of it as mulch.

The Happy Seeder is kinder to the environment and brings long-term economic benefits, according to a detailed assessment[9] by the Australian Centre for International Agricultural Research (ACIAR) . But farmers are not taking it up with much enthusiasm, at least in the Indian Punjab, according to Ridhima Gupta, from the Indian Statistical Institute in Delhi. Start-up costs and conservatism are undoubtedly among the reasons. Gupta is urging the Indian government to subsidise the machine, a process the ACIAR study says is already under way.

What has become clear from SANDEE’s research in pockets across South Asia is that there will be no uniform solution for a vast region of varied landscapes, farming practices, technologies and levels of awareness. Compare, for example, their studies in Pakistan, in the northwest and Bangladesh in the northeast.

In Pakistan, researchers looked at 400 farmers in two districts in Punjab who do not have Happy Seeders. Pulling the rice stalks up by hand pushes the farmers’ costs up by over a third – and is thus only worth it if there is a market for the residue, for example to feed livestock. Over 80% of the farmers did not know that technologies such as the Happy Seeder existed.

A study of 300 farms in southwest Bangladesh by Ziaul Haider of Khulna University considered farmers’ overall profit rather than just the costs of production. In this area, where the Happy Seeder also has yet to penetrate – researchers found that the farmers’ profit is as much as $111 (USD) higher per hectare if the residue is burnt rather than removed. This is not only because burning is cheaper than clearing, but also because the burnt fields produced greater yields of the next crop  (although the effects in the longer term are unclear). Paying farmers throughout the nation to abstain from burning would cost the government of Bangladesh $2.1 million (USD) a year – about 4% of current subsidies available to farmers for inputs such as fertilisers.

The breed of rice grown by farmers also influenced their decision to burn. Long-stalk rice is useful in the country’s ubiquitous, low-lying fields because it rises above floods. But it leaves behind voluminous, low quality stalks. These are not good enough for animal feed and so they are largely burnt. Haider found that farmers are growing the cheaper, long-stalk rice at higher elevations as well: subsidising and educating farmers to switch to short-stalk varieties at higher elevations might be a promising way forward. At low elevations farmers should instead be educated, and perhaps subsidised, to incorporate the long-stalk residue into the soil rather than burning it.

Haider also thinks there is scope for science to come up with a better variety of rice, for example one with a shorter growth period that would increase the time available after harvest before it is necessary to plant the wheat. That would leave enough time to deal with the residue in ways other than burning.

Whatever the solution, Shyamsundar says, the research shows that the problem is more tractable than dealing with other causes of climate change. This is because it’s a behaviour that causes tangible problems, such as local pollution, as well.

Perhaps the private sector – such as the aviation industry – could be encouraged to get involved in technology subsidies, she suggests.

“Planes can’t take off or land because of this really crazy smog that descends during the winter – that’s enormously costly.”  

It is fine-textured work such as this that will move things forward, she says.

“Big-picture studies are very powerful to us who work at a micro level – it’s a place to hang our hats on. But, on the other hand, if there is to be change it has to happen at the local level, there’s no other way of doing it. We have got to understand the behavioural issues.”


[1] Bond T. et al. Bounding the role of black carbon in the climate system: A scientific assessment (2013),  Journal of Geophysical Research 118: 5380-5552, doi:10.1002/jgrd.50171. This assessment resulted from IGBP-IGAC/WCRP-SPARC Atmospheric Chemistry and Climate Initiative (AC&C). The authors acknowledge financial and technical support from the International Global Atmospheric Chemistry (IGAC) project (one of the projects affiliating to Future Earth) and others.

[2] Gustafsson et al., Brown Clouds over South Asia: Biomass or Fossil Fuel Combustion? (2009) Science 323 (5913): 495-498, doi:10.1126/science.1164857

[3] Ramanathan V. and Carmichael G.,  Global and regional climate changes due to black carbon (2008) Nature Geoscience 1: 221-227 doi:10.1038/ngeo156

[4] Janssen N. A. H. et al. Health effects of black carbon (2012), World Health Organization Regional Office for Europe.

[5] Pant K. P., Monetary Incentives to Reduce Open-Field Rice-Straw Burning in the Plains of Nepal (2013), SANDEE Working Paper No. 81-13, 33pp.

[6] Gupta  R., Causes of Emissions from Agricultural Residue Burning in North-west India: Evaluation of a Technology Policy Response (2012),  SANDEE Working Paper No. 66-12, 25pp.

[7] Ahmed T. and Ahmad B., Why Do Farmers Burn Rice Residue? Examining Farmers' Choices in Punjab, Pakistan, (2013), SANDEE Working Paper No. 76-13, 33pp.

[8] Haider M. Z., Options and Determinants of Rice Residue Management Practices in the South-West Region of Bangladesh, (2012), SANDEE Working Paper No. 71-12, 27pp.

[9] Saunders C. et al. Rice–wheat cropping systems in India and Australia, and development of the ‘Happy Seeder (2012), ACIAR Impact Assessment Series Report No. 77, 48pp.