A new study says the world must reduce short-term climate pollutants as well as carbon dioxide to achieve the goals of the Paris Agreement

Climate policy, which relies solely on decarbonisation, is not enough to keep atmospheric warming below 2 degrees Celsius, and instead of curbing climate change, it will contribute to additional warming in the near future. a study published Monday in the Journal of the Proceedings of the National Academy of Sciences concludes. The study found that limiting warming in the coming decades, as well as in the long run, requires policies that focus not only on reducing carbon emissions but also “short-lived climate pollutants” – greenhouse gases including methane and hydrocarbons (together with hydrocarbons). carbon, or soot.

“We are participating in two races at the same time to prevent a climate catastrophe,” said Gabriel Dreyfus, chief researcher at the Institute for Management and Sustainable Development and lead author of the study. “We need to win the sprint to slow warming in the short term by fighting short-term air pollutants so we can stay in the race to win the marathon against CO2.”

The study used climate models to assess how the planet would respond if countries tackled climate change solely through decarbonisation efforts, namely the transition from fossil fuels to renewables, without containment of methane and other short-lived but strong climate pollutants.

The authors found that efforts to decarbonize only would lead to increased warming soon. This is because the combustion of fossil fuels releases both carbon dioxide and sulfates. Unlike carbon dioxide, which heats the planet and stays in the atmosphere for centuries, sulfate the particles reflect sunlight back into space, but remain in the atmosphere for only a few days, so they have a powerful but short-lived cooling effect.

The continued release of sulfates from burning fossil fuels now offsets warming by about half a degree that the planet would otherwise experience from carbon emissions when burning fossil fuels, Dreyfus said. Switching to renewable energy is quickly eliminating the short-term limitation of warming provided by sulfate emissions, and the planet will continue to heat for decades before long-term cooling from reduced carbon emissions, she added.

However, if emissions of methane, HFCs, soot and nitrous oxide occur simultaneously with decarbonization, both short-term and long-term warming can be reduced, Dreyfus said.

The current study is not the first to identify the need to tackle short-term climate pollutants along with reducing carbon emissions to curb climate change. In 2018, the UN Intergovernmental Panel on Climate Change noted that the reduction of short-term pollutants in the climate was required for any effort to limit warming to 1.5 C.

However, more recent reports, such as the IPCC’s sixth assessment, a three-part report published in 2021 and earlier this year, have sent mixed messages about the need to reduce short-term emissions into the climate, Dreyfus and co-authors said.

The first report in the series, prepared by Working Group I, focuses on the science of climate change and emphasizes the need to reduce short-term climate pollutants. The report notes that almost half of all the warming the planet has experienced to date comes from greenhouse gases other than carbon dioxide.

However, Working Group III, which prepared the final report of the series and focused on climate policy, placed too much emphasis on the long-term effects of carbon dioxide and focused too little on rising temperatures in the near future, Dreyfus and her authors said.

“If you’re going to get one and a half degrees in 10 years and then you get two degrees in about 25 years, that’s what we need to focus on,” said Virabhadran Ramanathan, a professor of atmosphere and climate science. at the Scripps Institute of Oceanography and co-author of the study. “We need to reduce short-term pollutants so that there are no short-term disasters in the next 25 years without losing long-term ones.”

David Doniger, director of the Climate and Clean Energy Program at the Council for the Protection of Natural Resources, who was not involved in the current study, agreed.

“Until recently, it could be said that CO2 sucked all the oxygen out of the room in international negotiations and domestic policy-making,” he said. “We now know that we need to quickly contain extremely powerful, short-lived, non-heat-polluting pollutants to meet the immediate problem, as well as limit CO2 itself in the long run.”

In recent political efforts, the United States and other countries have begun to focus on short-term air pollutants along with carbon dioxide. Last year, more than 100 countries pledged collectively reduce methane emissions by 30 percent by 2030. However, these reduction targets are voluntary, and it remains unclear how the U.S. and other countries will achieve their goals.

Similarly, more than 100 countries have ratified an international agreement in recent years to gradually reduce HFC production and use. The agreement, known as the Kigali Amendment to the Montreal Protocol, is expected to eliminate additional half-degree warming by 2100.

The EPA recently passed resolutions on the gradual reduction of HFCs, in line with the reductions provided for in the Kigali Amendment, but the United States has not yet ratified the international agreement. The amendment, which enjoys rare bipartisan support as well as industry, passed a vote in the Senate Foreign Relations Committee earlier this month; a full vote in the Senate is not yet scheduled.

Dreyfus said efforts to reduce methane, HFCs and other short-term pollutants will now be crucial to curbing warming in the coming decades.

“We know what levers are being pulled to slow this warming in the short term,” she said. “We just need to intentionally make it part of our strategy.”