First, the good news: 1,500 climate policies aimed at reducing emissions of planet-warming greenhouse gases have been implemented across dozens of countries over the past two decades.
The more troubling news: Only around 4 percent may have substantially reduced emissions, according to a new study.
“We’re finding good and bad news together,” said Nicolas Koch, a climate economist at the Potsdam Institute for Climate Impact Research and a co-author of the study published Thursday in Science. “It’s highlighting opportunities, like that larger reductions are possible, but also challenging the political will for policy design.”
While 63 policies highlighted in the study successfully reduced as much as 1.8 billion metric tons of carbon, the United Nations estimates that emissions must fall by 23 billion metric tons by 2030 to reach targets laid out in the 2015 Paris Agreement. Those targets aimed to limit the increase in the global average temperature to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, in order to preserve a livable planet.
With less than a decade left before that benchmark, the research could provide models for the best paths forward. “There is no silver bullet policy solution for climate mitigation,” said Jonas Meckling, an associate professor at University of California Berkeley and a climate fellow at Harvard Business School.
Most of those emissions reductions were tied to price instruments like changes in carbon prices, energy taxes and fossil-fuel-subsidy reforms. And most emissions reductions gained strength in numbers: They happened from the combination of multiple national policies, instead of just one stand-alone policy.
It’s often a combination of carrots and sticks, Dr. Meckling said, where the carrots are public spending like subsidies or tax credits, and the sticks are approaches like regulations on power plant emissions.
“Countries can learn from each other,” Dr. Koch said. If every country implemented one of the best practices that led to an emissions gap, up to 41 percent of the gap could be closed by 2030, he said. “It shows that we can implement powerful climate policies that lead to large emissions reductions.”
The study used statistical models to identify 63 drops in national emissions across 41 countries. Those drops of at least 5 to 10 percent in emissions are called breaks. In charts, they show up like steps down a staircase, sometimes gradual and sometimes steep.
Once these breaks were identified, a machine-learning model combed through a data set released by the Organization for Economic Cooperation and Development that identified 1,500 climate policies implemented between 1998 and 2022. Those policies cover four sectors: electricity, industry, transportation and buildings. Researchers then tried to match which policies could be attributed to which breaks in emissions.
“It’s the broadest empirical evidence to date for the insight that policy mixes or combinations of policies are needed to reduce greenhouse gas emissions,” Dr. Meckling said.
The United Kingdom, for example, reduced emissions up to 50 percent by 2015 from implementing a minimum price for carbon in the power sector, along with subsidies for renewable energy and an announcement of a coal phaseout plan.
But the study has drawbacks. Agriculture and land use change, a major emissions sector, was not included. Good data showing reductions in carbon emissions for that sector doesn’t yet exist, Dr. Koch said.
In addition, hundreds of countries are missing from the O.E.C.D. data, particularly developing economies in Africa, Latin America and the Caribbean. While some transitioning nations like Russia, Brazil, India and China are included, only one African country, South Africa, is part of the data set.
In addition, the study covered only the near-term effects, and effects within the country where the policy was adopted, said Jessika Trancik, a professor at the Massachusetts Institute of Technology. “But in climate change mitigation, we care about the effects on a global scale and bringing emissions down to zero regardless of where emissions reductions start,” she said. “So the fact that 63 cases were detected to have a significant impact over the near term where the policies were adopted, it doesn’t mean other policies weren’t effective.”
There are two main ways a climate policy can be effective. The first is to reduce emissions at a certain place and time. The second pathway is to develop technology that will allow for emissions cuts in the future, perhaps across multiple locations, like lower-cost solar panels resulting from technological advances. Emissions cuts plus development of new technology can create a positive feedback loop that the study might not be able to capture, Dr. Trancik said.
“Many of the technological tools that are needed to address climate change are now available,” Dr. Trancik said, “and ready to be adopted at scale because of a host of different types of policies that came before.”
Read More: Many Climate Policies Struggle to Cut Emissions, Study Finds
