Where on Earth have you got the idea that anyone thinks these factors won't continue to have effects in the future?
The 3 things mentioned are considered the most important factors in determining subdecadal global average surface temperature fluctuations. However, since they essentially oscillate around 0 their effect on multi-decadal trends is minimal, hence the overall trends in the full 1979-present reference period are unchanged.
Where they have a large effect is in shorter-term trends. For example, in the NOAA record the decadal trend from 1974-84 was 0.29ºC/Decade, from 1992-2002 0.33ºC/Decade; Conversely 1986-96 was only 0.08ºC/Decade and 1998-2008 0.06ºC/Decade. Even though the trends across the whole period are around 0.15ºC/Decade plotting across shorter periods reveals much greater variability - sometimes warming is 'faster', sometimes warming is 'slower' or perhaps even 'stopped'. What this paper has shown is that simply adjusting for these 3 factors leaves a much more consistent temperature progression. What that consistency means can be left to you as an exercise.
There are certainly potential problems with this approach, which may be worked out later in the literature, but it's a useful contribution to scientific understanding.