Most Climate Policies Don’t Work. Here’s What Science Says Does Reduce Emissions.

“The commonality in those successful cases is where we see subsidies and regulations being combined with price-based policy instruments,” said Nicolas Koch, senior researcher at the Berlin-based Mercator Research Institute on Global Commons and Climate Change and an author of the study. “This means carbon pricing, and it could be energy taxes, it could be vehicle taxes.”

The study, published today in the journal Science, used an AI algorithm to sift through a database of environmental prescriptions compiled by the Organization for Economic Cooperation and Development, a Paris-based economic agency, between 1998 and 2020. These policies ranged from energy-efficient standards for household appliances to a carbon tax on fossil fuels like oil and gas.

The fraction of policies that worked combined financial incentives, regulations and taxes, according to the study.

The authors evaluated policies adopted by each nation’s electricity, transportation, building and industrial sectors. They programmed the algorithm to cross-reference each policy with subsequent changes in greenhouse gas emissions from each country.

Cows graze near a coal-fueled power plant in Texas. Photo: Brandon Bell/Getty Images

Climate experts said the study is a good road map for which policies work and can be updated to include data from the 2022 Inflation Reduction Act, which is doling out an estimated $428 billion in subsidies, incentives and tax credits for climate-related projects.

“This study gives me confidence that we know what to do and how to do it,” said Julio Friedmann, chief scientist at Carbon Direct, a New York-based carbon management firm, who wasn’t involved in the study.

In 2015, more than 190 nations signed the Paris agreement, pledging to limit global warming to 1.5 degrees Celsius above preindustrial levels to avoid the worst effects of climate change. As part of the treaty, nations are required to document how they will achieve emissions reductions.

By searching through the OECD database, which identifies 46 types of policy interventions, the study’s authors found government policymakers prefer subsidies and regulations, according to Koch.

“We see a lot of policy packages built around these two policy types, and we find that it’s very rare that they really work in reducing emissions,” Koch said.

The study found the nations’ overall climate emissions will exceed the Paris target by 23 billion metric tons of CO2 by 2030.

The 63 successful policy interventions in total reduced emissions between 0.6 billion and 1.8 billion metric tons of CO2. The most successful of the policies included a mixture of policy tools to change consumer and corporate behavior.

In the U.S., emissions from vehicles dropped 8% from 2008 to 2010 after new mileage rules were put into effect in 2007 along with a tax break for motorists who bought cleaner cars in 2006, Koch said.

In the U.K., a combination of an announced phaseout of coal plants, a minimum price for electricity and stricter air pollution standards led to a 44% cut in emissions in the electricity sector between 2013 and 2020.

In China, emissions fell 20% in 2016 from the industrial sector in seven provinces that started an emissions trading program in 2013 that ratcheted down the use of fossil fuels, combined with the elimination of fossil fuel subsidies.

In isolation, policies such as labeling appliances or cars as energy efficient, imposing speed limits or imposing new vehicle taxes, weren’t sufficient to bend the emissions curve, the study found.

One limitation of the study is that it only examined policies that had an impact within approximately two years of implementation. However, some policy changes take longer to make a difference, according to Christoph Bertram, associate research professor at the Center for Global Sustainability at the University of Maryland, who wasn’t part of the study. Within the framework of the study, those kinds of policies wouldn’t appear to have reduced emissions.

Bertram pointed out the slow transition from coal to natural gas in U.S. power plants that began in 2007 and resulted in a 25% reduction in CO2 emissions by 2022. This transition didn’t result in a sharp reduction in emissions, and therefore wasn’t picked up as a success in the study, he said.

Experts say finding the right mix of climate policies is needed to forestall the kind of destructive flooding, droughts and other extreme weather that scientists expect to worsen as the world warms. The planet has experienced 14 straight months of record high global average temperatures, according to the National Aeronautics and Space Administration.

While the study reveals some successes, the policies aren’t being implemented at the scale to make a difference, according to Janna Hoppe, a researcher who studies climate policies at ETH Zurich, a Swiss university.

The study “has this empirically demonstrated track record of climate policies that have been working,” Hoppe said. “At the same time, they have not put us in a position where reaching climate neutrality is going to be easy to do in the next 30 years.”

Having a better policy road map like this study, she said, will help achieve that goal.

Write to Eric Niiler at eric.niiler@wsj.com