A new paper has shown that approximately 15% of current global warming (about 0.3°C) from human emissions stems from pollutants that fall outside most existing climate policy frameworks.
Most of these overlooked pollutants are called ‘indirect greenhouse gases’ and include carbon monoxide, non-methane volatile organic compounds, nitrogen oxides and molecular hydrogen.
The authors of the paper include several prominent figures in climate science and policy, including Steven Hamburg, Chief Scientist at the Environmental Defense Fund and Rick Duke, former US Deputy Special Envoy for Climate.
Unlike traditional greenhouse gases such as CO2, the warming impact of indirect greenhouse gases doesn’t come from trapping heat directly. Instead, these gases trigger chemical reactions in the atmosphere that can increase the abundance of methane, ozone and other greenhouse gases, producing warming as a result.
Scientists have studied these effects for decades, but the gases have never been incorporated into key climate policy frameworks, such as the Paris Agreement or the underlying UN Framework Convention on Climate Change. This means most countries are not accounting for the impacts of these gases in their climate targets and policies or developing strategies to reduce their warming impacts despite their significance.
Ilissa Ocko, a Senior Climate Scientist at Spark Climate Solutions and former Senior Advisor to the U.S. Special Presidential Envoy For Climate said: ‘Among all human-caused emissions that warm the climate, indirect greenhouse gases collectively rank as the third-largest contributor to the warming we experience today after CO2 and methane and ahead of nitrous oxide, hydrofluorocarbons and black carbon.
‘This is a significant contributor to warming that has been left out of climate policy discussions for far too long.’
The exclusion of indirect greenhouse gases traces back to the Kyoto Protocol, drafted nearly 30 years ago, which established the ‘greenhouse gas basket’ that continues to shape climate policy today. At the time, the climate impacts of indirect greenhouse gases were not well understood, but scientific understanding has advanced considerably since then.
Tom Grylls of Clean Air Fund, another of the paper’s co-author, added: ‘We already know that many indirect greenhouse gases are themselves harmful air pollutants, and contribute to the formation of toxic ground-level ozone. That means most countries do not need to start from scratch.
‘There are opportunities to build on existing air quality policies and monitoring systems to reduce these pollutants and their climate effects. Doing so would deliver immediate air quality and public health benefits, while also tackling an often overlooked source of global warming.’
Photo: geralt