Research done in 2014 explains very well the variations observed in global surface temperature. The variations are due to heat being stored in ocean depths and released from ocean depths. The important conclusion was that variations will cease shortly after year 2030; beyond then the rise in global surface temperature will be steady.
This article reports a simple calculation that gives a similar conclusion.
This is the surface temperature-index graph:
Only since ~1975 has the global temperature consistently increased. Prior to then there was cooling pollution that was cut back by U.S. and U.K. Clean-Air acts in the 1950s and 1960s.
The yearly change in global surface temperature is:
This is a plot of the maxima and minima of the global surface temperature:
The difference between the maxima and the minima is getting smaller. The two linear fits to the maxima and minima cross at ~2043.
Put these linear approximations for the maxima and minima with global temperture and its projection to 2050 yields:
However, the rapid rise in global temperature from 2013-2016 may indicate a new phase change, possibly due to rapidly increasing methane emissions.
L. David Roper interdisciplinary studies
L. David Roper, http://www.roperld.com/personal/roperldavid.htm