Emissions of carbon monoxide and volatile organic compounds have contributed significantly to planetary warming, according to new research. These indirect greenhouse gases account for about 15 percent of the temperature rise since pre-industrial times. Few nations currently address them in climate plans.
The pollutants react in the atmosphere to form ozone and reduce levels of hydroxyl radicals that break down methane. Together with black carbon they have caused 0.3 degrees Celsius of warming, offset partly by aerosols and nitrogen oxides.
Ilissa Ocko of Spark Climate Solutions said these forgotten pollutants strongly contribute to current warming and could slow future temperature rise if included in policies. Alex Archibald of the University of Cambridge noted that cutting them offers low-hanging fruit to avoid tipping points.
The gases break down within hours or years, so reductions would quickly lessen their impact. Sources include fossil fuel combustion, vehicle exhaust, forest burning and solvents. Air pollution rules in places like the UK have already cut emissions, yet many countries maintain weaker standards.
The US Environmental Protection Agency issued a regulation in January that scientists say weakens controls on nitrogen oxides from gas power plants. Researchers recommend nations mention these gases in Paris Agreement submissions and set reduction targets.