Air pollution body to crack down on black carbon

A controlled burning of a farmer's grass field burned near Lellinge, south of Copenhagen, Denmark, on 23 August 2021. (Credit: Keystone/EPA/Mads Claus Rasmussen)

The convention on air pollution is due to issue voluntary measures this week to curb black carbon emissions.

The convention on air pollution will be meeting from 6 to 8 December in Geneva, where it will adopt guidelines on how to reduce emissions from agricultural waste burning, including black carbon – a gas that is 680 times more heat trapping than CO2.

Since October 2019, 25 of the 51 pan-European parties to the air convention that have signed the amended Gothenburg Protocol– including Switzerland, the EU, the US and Canada – are legally required to reduce their fine particulate matter (PM2.5) emissions.

The measures, which are voluntary, are part of a growing shift of attention towards the need to bring down greenhouse gas emissions other than carbon dioxide in order to keep the world from warming up. Last week, the International Maritime Organization also agreed on non-binding measures to reduce black carbon emissions from the shipping industry in the Arctic.

What is black carbon and why does it need attention?

Black carbon, or soot, are tiny dark particles that rise from chimneys, wildfires and fossil fuel burning. As they go up in the atmosphere, they mix with water droplets and other elements, degrading air quality but also absorbing sunlight.

As a powerful heat trapping gas, studies suggest black carbon could also possibly be the second main driver of climate change right after CO2. Black carbon only stays a few weeks in the atmosphere, unlike CO2 which accumulates and remains in the air for decades, making the argument that slashing black carbon emissions would be a quick and easy fix to limit the rise in temperatures.

Agricultural waste burning and wildfires are the largest source of black carbon, making up roughly a third of emissions. However, practices such as open crop burning or forestry residue burning have long been viewed as a harmless and cheap way for farmers to clear land.

“In terms of CO2 emissions, agricultural residue burning was long considered essentially ‘carbon neutral’, because it was assumed the same amount of carbon lost to fire would be fixed by the subsequent year’s crop,” the report points out.

“As understanding of soil carbon cycles has grown, however, it has become clear to the vast majority of researchers that, due to loss of humus, soil structure and the soil itself, more carbon is lost from the soil annually than can be replaced by any subsequent crop.”

The deterioration of the soil can also have negative economic effects by causing nutrient loss and soil productivity, not to mention the impact on biodiversity, according to the document.

Among the issued guidelines, the air quality regulating body recommends that countries use fire-free alternatives, such as conservation agriculture, and chopping and spreading of the excess harvest residue or repurposing it off-field. These can in turn help build up climate resilience.