One of the major initial sources of concern regarding anthropogenic global warming (AGW) was a paper published by Hansen et al. in 1988: Global Climate Changes as Forecast by Goddard Institute for Space Studies Three-Dimensional Model.
Hansen provided three scenarios:
(A) growth in rates of trace gas emissions typical of the 1970s and 80s will continue indefinitely, giving an increase of 1.6C by 2020;
(B) decreasing trace gas growth rates such that the annual increase of greenhouse climate forcing remains constant at the present level, giving an increase of 1.2C by 2020;
(C) drastically reduce trace gas growth between 1990 and 2000 such that greenhouse climate forcing ceases to increase after 2000, giving an increase of 0.6C by 2020.
Clearly, with CO2 now over 400ppm, the world has followed Scenario (A). However, the current global temperature increase is in the range of 0.3 – 0.4C.