Only a handful out of hundreds of climate policies that have been implemented around the world over the last two decades have appreciably reduced emissions, according to a new study. But the analysis also identified which approaches work best to lower emissions in different industries and economic conditions, providing a road map for future improvements.

Countries’ efforts to reduce greenhouse gas emissions are likely to fall drastically short of what’s necessary to meet the goals the Paris Agreement, with an estimated emissions gap of 23 billion metric tons of carbon dioxide by 2030. This is both because countries aren’t making ambitious enough promises and because the policies they put in place often don’t work as well as planned.

Until now, there has been little consensus on which climate policies reduce emissions most effectively at a large scale. Past research on climate policy effectiveness has tended to focus on just a few well-known policies, ignoring hundreds more.

In the new study, researchers leveraged a fantastically comprehensive climate policy database recently assembled by the Organization for Economic Co-operation and Development (OECD). They analyzed the effects of 1,500 climate policies implemented between 1998 and 2022 in 41 countries around the world that account for over 80% of global emissions.

The database includes 48 different climate policy types ranging from energy-related building codes and other regulations to subsidies for the purchase of climate-friendly products to carbon taxes. It covers the introduction of new policies as well as tightening of existing policies, and captures the effect of suites of policies implemented around the same time.

Because of the multitude of different policies and combinations at play, the researchers turned to a machine learning approach for their analysis, employing a version of a statistical technique commonly used to estimate the causal effect of an intervention.

Only 63 of the 1,500 policy interventions actually produced an appreciable reduction in carbon emissions, the researchers report in a paper published in the journal Science.

Most of the successes were achieved by a combination of two or more policies, and the analysis suggests that combining policies was often more effective than single measures on their own, in contrast to arguments made by some that this would be redundant or overkill.

For example, subsidies or regulations alone don’t work – they have to be combined with price-based instruments like carbon and energy taxes. Simply banning coal-fired power plants or combustion engine cars has not reduced emissions, but can do so when implemented in conjunction with taxes or price incentives (as with coal plants in the UK and cars in Norway).

“In most cases, we found that effect sizes are larger if a policy instrument is part of a mix rather than implemented alone,”

“In most cases, we found that effect sizes are larger if a policy instrument is part of a mix rather than implemented alone,” the researchers write. The analysis highlights the role of less-heralded policies in emissions reduction success stories that have previously been chalked up to single policies.

For example, reductions in emissions from the UK electricity sector in the mid-2010s didn’t just happen because of the introduction of a carbon price floor, as is commonly supposed, but because of a variety of policies implemented around the same time. Also in the middle of the last decade, emissions reductions in China’s industrial sector came about not just because of the advent of emissions trading schemes but also due to the reduction of fossil fuel subsidies and strengthening measures to encourage energy efficiency investments.

The results clarify the best bets for reducing emissions in the building, electricity, industry, and transport sectors in both industrialized and developing nations. In theory, scaling up these successful policies could close the emissions gap. The researchers also built an interactive website, the Climate Policy Explorer, where the public can see the methods and results of the analysis.

Source: Stechemesser A. et al. “Climate policies that achieved major emissions reductions: Global evidence from two decades.” Science 2024

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Climate policies that achieved major emission reductions: Global evidence from two decades