Abstract: Two climatologists and a theoretical physicist were awarded the 2021 Nobel Prize in Physics “for groundbreaking contributions to our understanding of complex physical systems”. Many of us might be surprised why two climatologists have won the 2021 Nobel Prize in Physics. The committee of the Nobel Prize in Physics specifically pointed out that the understanding of global warming is founded on solid physics, and that the winning of the prize by the two climatologists is because they developed models based on physical principles to simulate the climate system, quantify climate variability, and reliably predict global warming. The prize indicates the importance of solving complex problems in the realistic world, especially the problem of global greenhouse warming. Here I address the scientific contributions of the two climatologists, focusing particularly on how they contributed to developing climate models and methods to solve the problem of global warming caused by anthropogenic activity.