Abstract: Regardless of more than 30 years’ efforts, the large uncertainty of climate sensitivity (1.5 to 4.5oC for 2XCO2) could not be reduced. With such a large uncertainty, claiming consensus on “current global warming is mainly caused by human being activities” is simply a joke. Why is this uncertainty so difficult to reduce? Can we expect the uncertainty be reduced in the near future based on the current research efforts? What is the effective approach for reducing this uncertainty? This presentation will address these questions from both observation and model perspectives with exciting preliminary results.