Cities are home to over half the world’s population and produce around 75% of its carbon emissions, but they’re leading the way in the global fight against climate change.

The 2015 Paris Climate Agreement demanded that by 2020 cities reduce their emissions by 20% compared to 1990 levels. But the EU’s Covenant of Mayors set a more ambitious target of 27%. And they’re well on the way to meeting that, according to a new report by the European Commission’s Joint Research Center.

The cities have already seen a 23% overall reduction, with the building sector performing the best—dropping its emissions 27%.

The long-term goal is 40% reductions by 2030. To meet that, cities will have to target reducing emissions due to transport, a sector that has only dropped its emissions by 7% since 1990, according to the report.

The encouraging numbers came amid a bleak atmosphere for climate activists in the US, given president-elect Donald Trump’s appointment of climate denier Myron Ebell to lead the administration’s Environmental Protection Agency transition. And renowned social scientist Benjamin Barber believes American cities hold the way to protecting the future.

“Cities have a very large role to play,” he said in a recent interview. “Most greenhouse gas emissions come from cities and cities also control about 80% of GDP. They can do a lot to combat climate change, whether or not Trump undermines the COP21 agreement.”

The signatories to the Covenant of Mayors have a combined population of 213 million—around 8% of the world’s population. Most of the cities involved are in Europe and Central Asia.

Correction: An earlier version of this article stated that the Covenant of Mayors was jointly headed by the EU and former New York mayor Michael Bloomberg. Bloomberg has no official role in the Covenant of Mayors, but will become joint-head of the Global Covenant of Mayors in January, when the EU project merges with Bloomberg’s own Compact of Mayors project.