Climate change is one of the greatest challenges faced by mankind in the 21st century. In layman’s terms, this talk illustrates the basic inner working of the Earth’s climate system, and the underlying physics responsible for global warming. It starts with a synthesis of the gathering observational evidences for a warming Earth. Then, it reviews the construction and capabilities of global climate models (GCM), as a crucial tool for studying climate change. The major gaps in the state-of-the-art understanding of manmade climate change are highlighted. It concludes with a summary of the key findings in the authoritative assessment report released by the Nobel Prize-winning Intergovernmental Panel on Climate Change (IPCC).