In August 2021, the Working Group Ⅰ(WGI) report of the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) was released.The report has concluded that human activities have warmed the atmosphere, ocean and land.Widespread and rapid changes in the atmosphere, ocean, cryosphere and biospherehave occurred.This paper presents the main conclusions of the report on the impact of human activities on the climate system, including the impact of human activities on the atmosphere and surface, the cryosphere, the ocean, the biosphere and the climate variability.It is clear that based on recent literatures in the filed of climate change detection and attribution, anthropogenic forcing signal, which is dominated by greenhouse gases, has been detected in multivariable changes in the climate system.The uses of the newest observational data, the latest generation of climate models and the updated attribution methods provide solid basis for these conclusions.