Abstract: Governments and their citizens in different countries around the world are increasingly concerned with the potential impact of climate change on society and the environment.Society is also becoming increasingly vulnerable to severe weather events and climate extremes,which are projected to increase in frequency in a warmer world.It is thus important to understand recent changes in global climate and the occurrence of extreme events in the late 20th century,to better deal with projected climate change scenarios for the 21th century.This paper summarizes the results of climate change studies over different countries and regions.The results are based on scientific articles,reports and assessments already available in the literature.We first introduce regional climate variations in the late 20th century based on observations and analysis.We then discuss climate change scenarios based on the IPCC (Intergovernmental Panel on Climate Change) scientific report.Uncertainties in climate change projections and opinions of skeptics of human-induced climate change are also reviewed.Finally,the potential impact of climate change on society and the environment will be briefly addressed.