So the UK, with about 4.7% the population of China, produces 0.7% as much steel, i.e. the ratios are within an order of magnitude. And presumably what works in the UK will work in China too.

Almost every individual action by a single emitter makes a tiny contribution to AGW.

If the technology is developed and proven in a smaller economy, then it can be expanded to the bigger one by said smaller economy.

Doesn't China have a free pass with their emissions through to 2030, due to their "developing country" status?

Pretty sure that's the case, though they have to start reducing their emissions after that like the rest of us.