Executive Secretary of the UN Framework Convention on Climate Change (UNFCCC) Patricia Espinosa said that densely-populated cities such as Alexandria in Egypt and Osaka in Japan are particularly high-risk locations for the negative impact of climate change.
C cities, which produce about 70 percent of carbon emissions, are driving green reforms and will be key to tackling climate change, the United Nations' climate chief said on Thursday.
Their contribution to global warming could rise as two-thirds of the world will live in cities by 2050, up from about half now, the United Nations says.
"Cities are where the climate battle will be won or lost," said Espinosa during a conference of city and government officials in Germany on Thursday.
"We're seeing an incredible momentum for action in cities," she said, noting that city-level decisions, such as whether a local park would be built or electric buses installed, often felt more tangible to citizens than national reforms.
The 2015 Paris Climate Agreement has been ratified by 175 nations, with the goal of keeping the rise in average global temperatures to "well below" 2 degrees Celsius above pre-industrial times.
Espinosa spoke to Reuters as she readied for two weeks of "crucial negotiations" to finalise preparations for December's UN climate change summit, COP24, in Poland.
Cities are "indispensable" to tackling climate change as they bring together different strands of the economy and social activities, while many national governments cannot deliver reforms alone, she said.
"Never has our work been more needed or more urgent and 2017 made this very clear – it was nothing less than a climate disaster for many people," she said, citing floods, fires and droughts.
Extreme weather robbed millions in developed and developing countries of their lives, homes and jobs in 2017, she said.
"The impacts of climate change are not going to get better, they are going to get worse," she cautioned.
"We can avoid the worst of these impacts if we act now," she said, by ramping up city-level actions to build resilience by preparing for climate emergencies and investing in initiatives to address climate change.
"We have a lot ahead of us."