Everyone knows the major chemical culprits responsible for climate change—carbon dioxide and methane—but there are a handful of lesser emissions that contribute, too. Now, in a policy paper published today in Science, leading scientists and climate experts are calling for these overlooked pollutants to be monitored and regulated as well.
Unlike other emissions, these indirect greenhouse gases don’t trap heat themselves. Instead their chemical activity in the atmosphere contributes to global warming by increasing the prevalence of more traditional greenhouse gases. For example, carbon monoxide and volatile hydrocarbons can prolong the life of methane and promote the production of carbon in the atmosphere. Not all of the indirect greenhouse gases are implicated in warming the planet, however. Some, like nitrogen oxides and sulfur dioxide, can have cooling effects.
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Even though the volume of these emissions are dwarfed by carbon dioxide and methane, they still have an outsized impact. Scientists estimate indirect greenhouse gases contribute as much as 15 percent to global warming. But despite their pernicious effects, they’ve been left out of United Nations efforts to curb emissions. That’s partially because when the U.N. first took steps coordinating a global response to climate change through the Kyoto Protocol nearly 30 years ago, we simply didn’t know how they contributed to the problem.
Now, that’s changed, and scientists are urging policymakers to go “beyond the basket” of the pollutants originally addressed by the U.N. Framework Convention on Climate Change (UNFCCC). “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 carbon dioxide and methane—ahead of nitrous oxide, hydrofluorocarbons, and black carbon,” lead author Ilissa Ocko of Spark Climate Solutions said in a statement. “This is a significant contributor to warming that’s been left out of climate policy discussions for far too long.”
Of course, any climate policy discussions happening in the near future will take place without the United States. One of President Donald Trump’s first acts in office was withdrawing from the UNFCCC’s Paris Agreement. And so, it’s up to the parties that remain to make the necessary changes. 
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Lead image: Knut / Adobe Stock
