London Mayor Boris Johnson is visiting Paris to discuss tackling climate change and cutting carbon emissions with other leaders as crucial UN talks continue.
Mr Johnson is meeting senior politicians, including French president Francois Hollande and mayor of Paris Anne Hidalgo, and more than 100 city leaders from around the world who are gathered for a summit of "C40" cities - major world cities working to tackle global warming.
He is also joining the British Ambassador to France to lay a rose at the Bataclan concert hall, where gunmen stormed the building midway through an Eagles Of Death Metal concert on November 13, killing 89 people, including Briton Nick Alexander.
As part of his visit, he is discussing with Ms Hidalgo ways in which London can support Paris in the aftermath of the terror attacks on the French capital, which killed 130 people in total.
He is also championing London and Paris as tourist destinations and encouraging Londoners to continue to visit the French capital.
The main focus of his visit is tackling climate change, with London claiming to lead the way with a 14% reduction in carbon emissions since 2008 despite an increase in population of one million and economic growth.
The mayor has come under fire in the city for not doing enough to tackle London's air pollution problem, but will be discussing with other leaders his success in transforming the capital's bus network to make it greener and how working with other cities can drive down costs of new, cleaner vehicles.
He will also discuss plans to boost London's status as the clean tech capital of the world, boost research and innovation and deliver the world's first ultra-low emissions zone in a bid to improve London's air quality and reduce carbon emissions.
Mr Johnson said: "It's vitally important that world cities unite and work together to mitigate climate change.
"London's thriving green economy is worth over £30 billion and we are a leading centre of innovation, with the entrepreneurs, technical ability, academia and engineering to drive the transition to a low carbon economy.
"We've proven in the capital that unprecedented population increases are no barrier to reducing carbon emissions and I look forward to discussions with my fellow mayors that help deliver a positive environmental impact."
Mr Johnson is visiting a thermal power station owned by Engie which uses water from the River Seine to cool five million square metres of public buildings, including the National Assembly, lowering their carbon emissions by reducing the need for individual air-conditioning.
He wants to help bring in a similar scheme in Greenwich, which will use the Thames to produce hot water from heat pumps to warm local homes, with the aim of improving air quality by lowering emissions from boilers and reducing energy bills for residents by around 10%.
His visit comes as negotiators from 195 countries at the UN climate summit attempt to hammer out a new comprehensive deal to curb greenhouse gas emissions and prevent "dangerous" climate change.