AMSTERDAM (AP) - The struggle to contain climate change usually focuses on reducing carbon dioxide. But black carbon and ozone, the main ingredients of soot and smog, also add to global warming, and controlling them will act quickly to slow rising temperatures, a U.N. agency said Tuesday.
Black carbon comes from solid particles from tailpipes, forest fires or wood-burning stoves and brick kilns commonly found in poor countries. It absorbs sunlight, and is most damaging when it settles on the Arctic snow or mountain glaciers, causing ice packs to melt more rapidly.
Another climate changer is ground-level ozone, said the U.N. Environment Program. Ozone, which is largely formed from methane, is beneficial as a high-altitude blanket around the Earth, but at 10 to 15 kilometers (6-9 miles) above the surface it acts as a powerful greenhouse gas and a contributor to urban smog.
A study released at U.N. climate negotiations in Bonn, Germany, by UNEP and the World Meteorological Organization said big cuts in black carbon and ozone-forming methane not only would slow global warming but would curb respiratory diseases and reduce damage to crops.
Carbon dioxide, or CO2, mainly from burning fossil fuels by heavy industry and transportation, accumulates for centuries in the atmosphere, and has a long-term impact on global warming. Black carbon, methane and ozone are "short-lived climate forcers," and reducing them has a more immediate effect, the UNEP report said.
"We have not found a silver bullet," said UNEP's chief scientist Joseph Alcamo. "What we have found is a strategy for a very powerful compliment to needed CO2 reduction."
Johan Kuylenstierna of the Stockholm Environment Institute, the report's chief author, said taking steps to cut black carbon and ground-level ozone over the next 20 years would "significantly slow" anticipated global warming, making a difference of 0.5 degree Celsius (0.9 F) by mid-century.
It also would avoid 2.5 million premature deaths every year from air pollution and would raise crop production by 50 million tons annually, he said.
The report listed a 16 actions that should be taken.
Black carbon can be reduced with filters on diesel engines, taking old vehicles off the roads and replacing wood-fired cooking stoves and brick kilns with biomass fuels.
Ozone-building methane emissions can be slashed by recovering leaks from ventilation shafts in coal mines, gas facilities and pipelines, by separating and treating biodegradable garbage from municipal waste, and changing the diet of methane-emitting livestock.
Adopting such measures quickly would enhance the prospects of limiting the rise in global temperatures to 2 degrees Celsius (3.6 F) above preindustrial levels, the target set by international negotiators. One result would be a reduction in the projected warming of the Arctic over the next 30 by about two-thirds, it said.
"These are not measures that we have to invent. They already exist," Kuylenstierna told reporters in Bonn. But they must be implemented on a wide scale across the globe.
The long-term answer to climate change remains a sharp reduction of carbon dioxide, the most common and long-lasting greenhouse gas, he said.
Scientists warn that a global average temperature increase of more than 2 degrees raises the risk of disastrous climate changes effecting agriculture, sea levels and the survival of species.