The assessment by UN-Habitat said that the world's cities were responsible for about 70% of emissions, yet only occupied 2% of the planet's land cover.
While cities were energy intensive, the study also said that effective urban planning could deliver huge savings.
The authors warned of a "deadly collision between climate change and urbanisation" if no action was taken. Read the full report here.
Source: by Mark Kinver, Science and environment reporter, BBC News.