Black carbon’s global warming role ‘still unproven’

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The fine dust particles emitted from burning wood or fuel, referred to as black carbon, are "likely to play a role in climate change" but should not divert attention away from carbon dioxide, EU officials said.

Black carbon has recently been the focus of attention after some studies identified it as a major contributor to global warming, coming second only to CO2.

Dark smoke fuming from burning forests, the exhaust pipes of diesel cars or kitchen stoves that burn biomass absorbs sunlight and captures it as heat in the Earth's atmosphere, according to researchers. Moreover, it can affect precipitation patterns and cloud formation.

But EU policymakers speaking in Brussels yesterday (22 June) cautioned that more research must be carried out to ascertain its impact more accurately.

"From the scientific point of view, it is not that certain yet," said Frank Raes, head of the climate change unit at the European Commission's Joint Research Centre (JRC).

However, he said black carbon was "likely" to contribute to climate change.

In addition to climate change, the health implications of particulate pollution make a compelling case for tackling black carbon, speakers agreed. Like other small particulates, it causes premature death and respiratory disease, they claimed.

Raes argued that the regional impacts of black carbon may be even more significant than its global warming effect. In the Arctic or the Himalayas, for instance, soot settling on ice and snow cover is accelerating melt rates, he said.

While CO2 remains the biggest global warming culprit, the advantage of tackling black carbon is that it is short-lived and can therefore have a beneficial impact on the climate only 5-10 years after its emissions are cut.

CO2 remains top priority

But a senior Commission official warned against allowing the black carbon discussion to distract from the EU's focus on cutting CO2 emissions, which he said remains the top priority.

"We should be careful not to reverse priorities," said Niels Ladefoged, a member of Climate Action Commissioner Connie Hedegaard's cabinet, suggesting that the EU was already dealing with the problem under its air quality legislation.

The existence of both black and white aerosols, with warming and cooling impacts, makes it less straightforward to make a case for political action on black carbon, the speakers added.

Nick Nuttall, spokesperson for the UN Environment Programme (UNEP), said studies on black carbon would need more precision before policymakers could move forward. He suggested that the world could eventually start looking into creating a carbon fund for black carbon like that created to reduce emissions from deforestation and forest degradation in developing countries (REDD).

He confirmed that politicians seem to be nervous about "taking the eye off the CO2 ball and focusing it on something else".

The world has directed its efforts to fight climate change at reducing CO2 emissions.

However, scientists have warned that methane, 20-times more potent a greenhouse gas, is already seeping from the warming Arctic sea bed and thawing permafrost in Siberia and Alaska, and could lead to runaway climate change (EURACTIV 27/08/09).

Moreover, some researchers have recently started to draw attention to the climate warming potential of black carbon, a component of soot, which absorbs radiation and causes glaciers to melt when the black dust settles on white snow and ice.

Asia has been identified the biggest source of the pollutant due to the burning of wood, dung and coal in cooking and heating stoves, burning fossil fuels in the industrial sector and using diesel fuel in cars, the use of which is increasing.

By contrast, black carbon emissions have been decreasing in developed countries.

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