Sir, Your editorial “Xi and Obama revive hopes on global warming” (November 13) is surely right to state that the joint announcement by the US and China on climate change will “have breathed unexpected life” into the negotiations about a new international agreement due to be finalised in Paris in December 2015.

But you are unjustifiably cynical about Xi Jinping’s reasons for making a joint announcement with Barack Obama, and it was wrong to describe as a “sop” the historic pledge to stop the growth in China’s annual emissions of greenhouse gases by 2030. The joint statement in Beijing by Presidents Xi and Obama follows detailed discussions about climate change that have been going on for more than a year between the two leaders and their governments. China and the US announced the establishment of a joint working group on climate change in April 2013, and at their first meeting in June 2013 in California the two presidents demonstrated their commitment to the issue with an important announcement about phasing out hydrofluorocarbons, a category of powerful greenhouse gases.

China understands the importance of limiting its greenhouse gas emissions, not just because it recognises the vulnerability of its population to the impacts of climate change but also because unabated use of fossil fuels is causing serious air pollution problems in its cities.