It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. The evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.
Qin Dahe, Co-Chair of IPCC Working Group 1, is even more specific:
Observations of changes in the climate system are based on multiple lines of independent evidence. Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased.
This clarity is not surprising. China's own 710-page Second National Assessment Report on Climate Change, released to the public last year, warns that China itself faces extremely grim ecological and environmental consequences from global warming. These impacts, including increasing droughts and floods, threaten China's already vulnerable food and water supplies, and rising sea levels will affect millions of people in Shanghai and other highly populated coastal cities.
The message is clear: every country must act now to step up their efforts on climate change, especially the U.S and China, the world's two largest greenhouse gas emitters. These countries agreed as much in a recent Joint Statement on Climate Change and have launched new cooperative programs to reduce emissions from coal and heavy duty vehicles, increase efficiency and renewables, and improve monitoring of GHG emissions.
China is also taking action on its own to fight climate change. It is closing heavily polluting factories, prohibiting new coal-fired power plants in major industrial regions, and investing more in renewable energy than any other country in the world. It is experimenting with CO2 cap and trade programs, debating a carbon tax and drafting a climate change law. NRDC is also working with China's top energy experts to develop a comprehensive, enforceable program that will put a nationwide cap on coal consumption, the leading contributor to climate change.
Many of China's actions are driven not just by climate change, but by other reasons such as energy security and the need to address choking levels of air pollution. Moreover, enforcement of laws, policies and programs remains a major challenge in China, in large part because of strong resistance from vested interests including state-owned fossil fuel companies and local government leaders who profit from polluting industries. But it is important to recognize that China is taking serious steps to combat climate change, and that other countries should not hide behind China as a reason for their own inaction.