To control climate change, the world must go beyond cutting carbon dioxide emissions and curb lesser-known pollutants such as nitrous oxide playing a key role in warming the planet, new research suggests.
Decades of global climate discussions have focused on CO2 emissions, which are most abundant in the atmosphere. The common goal of reaching "net-zero" emissions refers most often to CO2 emissions alone.
Over the last year, more than 100 countries have pledged a 30% cut by 2030 to emissions from methane, another carbon-based greenhouse gas that is far more powerful at trapping heat than CO2. Most of those countries have yet to say how they will meet that deadline.
Meanwhile, scant attention has been paid to other warming pollutants, including black carbon, also called soot, which absorbs radiative heat, as well as hydrofluorocarbons found in refrigerants, and nitrous oxides. But together with methane, these pollutants are responsible for about half of the warming seen today, according to the study published on Monday in the journal Proceedings of the National Academy of Sciences.
"When we're worried about the near-term … we need to look at the other non-CO2 climate forcers," said study co-author Durwood Zaelke, president of the Institute for Governance & Sustainable Development in Washington DC.
This is especially important as countries pursue CO2 reductions through cutting back on their use of fossil fuels, still considered the main contributor to global warming. Using fewer fossil fuels will result in less air pollution, including airborne sulphates that actually counteract some climate change by reflecting solar radiation away from Earth.
Scientists say these sulphates are masking about 0.5 degree Celsius of warming that would be seen without them, meaning aggressive climate action could see temperatures temporarily jump higher – unless the lesser pollutants are tackled as well.
A path of decarbonization alone would see the planet breach 2 degrees Celsius of warming beyond pre-industrial temperatures by 2045, the study finds.
Conversely, reining in all climate pollutants together could see the world begin to avoid some warming as early as 2030 and halve the rate of warming between 2030 and 2050, the findings suggest.
"This landmark paper should bring about a major rethink" of global targets, said Euan Nisbet, a climate scientist at Royal Holloway, University of London, not involved in the study. "If we don't also bring down non-CO2 warming, we cook."
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