In the past two decades, the cognition on the facts, causes and future trends of climate change has been strengthened due to the improvement of observational measures, the enhancement of analysis methods and the development of climate models. It is further confirmed that warming of the climate system is unequivocal, anthropogenic activity is the main cause of global warming since the mid-20th century and further warming will continue in the climate system in future. IPCC assessment reports on climate change have greatly promoted the progress of the physical sciences. They also lay the solid scientific foundations for adapting to and mitigating climate change.