The world is approaching a watershed moment in its battle to limit the risks posed by global climate change, and international leadership from the United States is needed now more than ever before.

A report by the Intergovernmental Panel on Climate Change in September warned that emissions of carbon dioxide and other greenhouse gases are already raising temperatures, melting glaciers and the polar ice caps, elevating sea levels and changing the strength and frequency of many extreme weather events.

Without sharp reductions in emissions, global average temperature could be much more than 2C degrees above its pre-industrial level by the end of the century, beyond anything the Earth has seen for millions of years, and way outside the experience of modern Homo sapiens.

The United States National Climate Assessment, published in draft form earlier this year, warned that the American people are already experiencing the consequences of global warming, and that their health and livelihoods will be even more at risk as temperatures rise further.

Rich countries, such as the United States, will not be able to simply adapt to the direct impacts. The Assessment points out, for instance, that sea level could rise by as much as four feet by the end of the century, potentially threatening nearly five million Americans who live within four feet of the local high-tide mark.

And the impacts of climate change on other parts of the world could also have severe consequences for the United States.

We have seen the disruption that was caused to global food supplies, for instance, by severe droughts which wipe out yields of important crops.

Not only do such extreme events cause hardship and suffering, but they also create the conditions for political instability. Hundreds of millions of people could begin to migrate away from the worst affected areas, with the potential for severe and extended conflict around the world.

Hence, even if Americans were concerned only about themselves, there are compelling reasons for the United States to promote an acceleration of international efforts to limit the risks of future climate change.

However, a recent analysis by the United Nations Environment Programme showed that the cuts in emissions that are currently planned by individual countries are collectively inconsistent with avoiding global warming of more than 2C degrees.

Countries are now seeking a new international agreement in Paris in 2015 to secure the greater action required to stay below the threshold for dangerous climate change, but little progress was made during the latest round of United Nations negotiations last month in Warsaw.

With the European Union currently dithering and unable to provide the leadership that it has previously shown on climate change, the stage has been set for the world’s two largest emitters, China and the United States, to set an example.

Despite the unwillingness of many in Congress to face up to climate change, the United States managed to reduce its overall greenhouse emissions by nearly 8% between 2007 and 2011, with carbon dioxide from energy use falling even further in the past two years.

But China is showing the greatest ambition. As its economy continues to expand, it is attempting to make a rapid transition to cleaner and more efficient growth.

China is investing very heavily in low-carbon energy, spending $10 billion on wind farms and almost $13 billion on nuclear power in 2012 alone. More than a fifth of its electricity was generated from sources other than fossil fuels last year.

However, China is not only the world’s largest consumer of clean electricity. It is also the biggest manufacturer of renewable energy technologies, such as solar panels.

For China, the global transition to low-carbon economic growth is not primarily a burden, but rather a race to exploit the huge opportunities created by new markets at home and overseas.

China’s leadership recognises that the transition to a low-carbon economy is likely to be full of innovation, discovery, investment and growth. Indeed, it will provide the growth story of the next few decades, and it will lead to a world that is cleaner, quieter, safer, and more biologically diverse, with stronger communities.

Earlier this year, China and the United States forged a strategic collaboration on climate change, in recognition of the risks and opportunities that the world faces.

It is through this kind of joint leadership that both countries can promote prosperity and well-being, not just for their own citizens, but for future generations across the world.

• Professor Lord Nicholas Stern is chair of the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science. He will receive the 2013 Stephen H. Schneider Award for Outstanding Climate Science Communication at a ceremony in San Francisco on 11 December