Chinese President Xi Jinping and US President Barack Obama have made a landmark joint announcement on climate that will provide a major jolt of momentum for international climate action. By putting clear emission targets on the table, these two leaders have made it clear they understand the risks of climate change - and the urgency of action.

A century from now, historians could look back and see this as a turning point: the moment when China and the United States took a leading role in the global shift away from high-carbon fossil fuels, toward strong economies that rely primarily on renewable energy and low-carbon technology.

The building blocks of this new, lower-carbon future are already in place. By using them intelligently, China and the US can show the world that a sustainable environment and a growing economy go hand in hand.

China, especially, is at a pivot point: after 30 years of rapid economic growth, its GDP fell to around 7.7 percent last year, the lowest since the 1997 Asian financial crisis. Poised at the final stages of industrialization and mid-way through a process of urbanization, China has made great strides in energy efficiency and renewable energy, installing 12 gigawatts of solar photovoltaic projects in 2013, 50 percent more than any other country has done in a single year. However, China is also the world's largest fossil fuel importer, making it more vulnerable than developed economies to volatile global energy prices.

A just-released report, China and the New Climate Economy, a project on behalf of the Global Commission on the Economy and Climate, with research led by experts at Tsinghua University, shows that China faces a series of important choices that will shape its future and affect the rest of the world. The opportunities for China in terms of clean air, increased energy security and dynamic growth are great, and so are the challenges.

Between now and 2030, China has the opportunity to become a high-income economy, but it needs sustainable economic growth to avoid getting stuck in a middle-income trap. A new climate economy that takes better care of the environment also presents many business and growth opportunities.