The 2021 Nobel Prize in Physics is awarded to two climatologists and a theoretical physicist “for groundbreaking contributions to our understanding of complex physical systems”. Many of us would be surprised why two climatologists win the Nobel Prize in Physics. Here I present you my reading of the 2021 Nobel Prize in Physics, by addressing the following aspects: why is the climate system is called a complex physical system? The global greenhouse warming in the past century and possible future warming. The physical basis and brief history of global greenhouse warming. What are the contributions of the two climatologists, based on physical principles, to modeling of Earth climate, quantifying climate variability, reliably predicting global warming, and detecting and attributing global warming to anthropogenic activity.