It is an increase in greenhouse gas forcing in the late 20th century of some 0.8 W / m2. (watertechbyrie.com)
They found that models with a strong feedback based on the seasonal cycle also had a strong feedback under increased greenhouse gas forcing. (ipcc.ch)
The reason global heat content is increasing is that there is a global energy imbalance caused primarily by the anthropogenic greenhouse gas forcing. (skepticalscience.com)