Figure1: Time series of global annual mean surface air temperatures

A thick red line shows the observed value. A thick black line shows the calculation result (average of four experiments with different initial conditions). Average temperatures from 1881 to 1910 are subtracted from both the observation and model values. A gray zone shows the range of the four experiment results with different initial conditions.

The Top Panel: All the factors of climate variations (natural + human activities) are considered. The Second Top Panel: Only the factors due to human activities are considered. The Third Top Panel: Only the natural factors are considered. The Bottom Panel: None of the external factors are considered.

It is suggested that the warming trend at the last 30 years of 20th century could not be reproduced without considering the factors of due to human activities. On the other hand, the warming trend in the early 20th (1910 to 1945) century could not be reproduced without considering the natural factors.