Definition: Generate an appropriate title for the given text. The generated title must be short and include the main topic of the text. The preferred titles are under fifteen words.
Input: By Roger HarrabinBBC environment analyst Carbon emissions from air-conditioning are expected to soar as temperatures climb and people become richer. But at a global mayors summit, Paris is showcasing a simple technology using water piped from the Seine to cool apartments near the Champs Elysees. London Mayor Boris Johnson said he wanted London to follow suit by cooling buildings using water from the Thames. "I don't like to admit it - but the French are ahead of us on this," he confessed. The system works by taking water from the river and piping it round people's homes like ordinary piped water air conditioning. In summer a heat pump is used to make the water even cooler by employing technology similar to a fridge. The mayors meeting in Paris City Hall is timed to coincide with the UN climate summit. It brings together half of the 80 mega-city mayors who are working together to tackle climate change. The chairman of the group, Eduardo Paes, Mayor of Rio, said the mayors represented 600m people and a quarter of the global economy. "We can be very effective," he said. "Sometimes governments move slowly - we can often move more quickly." The mayors said they had learned from each other to spread green solutions round the world. They claim to have collectively made 10,000 climate initiatives since 2009. They spoke about their favourite initiatives: Boris Johnson's team said since the Mayor was elected in 2008, carbon emissions in London were down by 14%, even though population had swelled. He said a major preoccupation was to find ways of finding a low-carbon way to provide the heating and cooling from natural gas, which made up nearly 50% of the city's emissions. Darren Johnson, Green member for the London Assembly, told BBC News: "On the whole Boris Johnson has been a real disappointment. He has expressed climate sceptic views and failed to meet most of the targets in his (climate) strategies." The global commission advised by Lord Stern concluded recently that climate change could only be tackled if new cities to house a burgeoning population could be planned less like Los Angeles and more like Paris. Climate change remedies 'affordable' Follow Roger on Twitter @rharrabin UN climate conference 30 Nov - 11 Dec 2015 COP 21 - the 21st session of the Conference of the Parties - will see more than 190 nations gather in Paris to discuss a possible new global agreement on climate change, aimed at reducing greenhouse gas emissions to avoid the threat of dangerous warming due to human activities. Explained: What is climate change? In video: Why does the Paris conference matter? Analysis: Latest from BBC environment correspondent Matt McGrath More: BBC News climate change special report

COP21: City mayors discuss green solutions