A study of greenhouse gasses released into the atmosphere in 2019 found that China is the biggest polluter of all; by a huge margin. China was responsible for 27% of all emissions. That's more than the United States, European Union, India, & Japan combined.
President Xi Jinping says China's emissions will peak by 2030, having increased by 1.7% last year, while the rest of the world saw a decline in pollutants due to the pandemic. However, Xi claims China will be at net zero by 2050, although he has yet to explain how that will be achieved.