Trees will be planted in London and Manchester on Wednesday in a charity's project to fight global warming.
Trees help fight pollution
The move aims to encourage businesses and members of the public to take action over the next five years and transform 20 cities around the world.
Madrid in Spain, Romania's Bucharest and Ethiopian capital Addis Ababa will also take part in the first phase of the project run by Trees for Cities.
Trees absorb carbon dioxide, the major cause of global warming.
London's carbon dioxide emissions are around 50 million tonnes each year.
More than 300 trees surveyed in New York took 145 tonnes of pollutants out of the air, the charity said.
Graham Simmonds, chief executive of Trees for Cities, said: "The onset of global warming is the most serious issue facing today's generation.
"Our experience in London over the last 10 years has taught us people and companies want to do something for the environment and our aim is to harness this enthusiasm and generate a greening renaissance in cities around the world."