Barack Obama aims for reduction of a quarter or more by 2025, while Xi Jinping sets goal for emissions to fall after 2030

US President Barack Obama looks on as Chinese President Xi Jinping speaks during a joint press conference in the Great Hall of the People in Beijing Photograph: Greg Baker/AFP/Getty Images

The United States and China have unveiled a secretly negotiated deal to reduce their greenhouse gas output, with China agreeing to cap emissions for the first time and the US committing to deep reductions by 2025.

The pledges in an agreement struck between President Barack Obama and his Chinese counterpart, Xi Jingping, provide an important boost to international efforts to reach a global deal on reducing emissions beyond 2020 at a United Nations meeting in Paris next year.

China, the biggest emitter of greenhouse gases in the world, has agreed to cap its output by 2030 or…