How do we know if the temperature increase is caused by anthropogenic emissions?
Computer models strongly suggest that this is the case. The following graphs show that 1) If only natural fluctuations are included in the models (such as the slight increase in solar output that occurred in the first half of the 20th century), then the large warming in the 20th century is not reproduced. 2) If only anthropogenic carbon emissions are included, then the large warming is reproduced, but some of the variations, such as the cooling period in the 1950s, is not reproduced (this cooling trend was thought to be caused by sulfur dioxide emissions from dirty power plants). 3) When both natural and anthropogenic emissions of all types are included, then the temperature evolution of the 20th century is well reproduced.
