There's no absolute slam dunk proof china is cheating, because nobody is interested in ferreting it out, with VERY justified evidence that they ARE cheating. The reason for this is that China is China: a growing economic and military power, holder of US bonds, seller of cheap products, buyer of oil, supplier of medium range missile parts. They've co-opted the entire world, so nobody wants to get them upset.
This is what I call the "china syndrome" - it explains such varied things as why the ecofascists who blather about the US not supporting anti-global warming give China a free pass to build a new coal-burning power plant every week, and why people can express self-righteous indignation over zimbabwe, while fawning and butt-kissing for the biggest dictatorship on earth.