But climate change is a stock problem more than a flow problem. It is the stock of greenhouse gases in the atmosphere (where they can survive for more than 100 years), rather than the current flow of such gases that is currently warming the climate. Viewed historically, the US clearly bears far more responsibility than China for the existing stock of greenhouse gases in the atmosphere.
But then, today's flows become tomorrow's stocks. So, China has some responsibility too. Unless, of course, we think in terms of emissions per person, in which case China seems to bear far less responsibility than the US because the US still emits more than 3 times more carbon dioxide per person as China.
But then, China emits more than the US per unit of production (even after adjusting for purchasing power parity), which means that production in the US is more carbon-efficient than production in China.
The bottom line is that both China and the US countries bear some responsibility for the climate change problem. But, in my view, China's responsibility is less given the US's historical contribution to the existing stock of GHGs and its continuing high level of per capita emissions. This doesn't mean that China should be off the hook for reducing its GHG emissions, but it's at least understandable that China refuses to commit to specific emissions reduction targets until the US makes a credible commitment to reduce its own emissions.