One of the flat lining forcings for instance is black carbon which up to that time showed a quite strong constant rising effect. (realclimate.org)
If you let the data speak for itself, and eschew cherry picking - it is obvious that there is a relatively constant rise in temperature from about 1910 to 1965, with a large aberration approximately coinciding with WW2. (skepticalscience.com)
The Mona Loa co2 record shows a smooth constant rise of co2 in the atmosphere, as one would expect from an accumulation resulting from the burning of fossil fuels. (realclimate.org)