There are valid reasons to conclude that long-term changes in solar output are a key driver of global climate.
In fact, evidence for the influence of solar variability emerges rather clearly throughout the climate swings of the past 2,000 years. Heightened solar output correlates remarkably well with both the Roman Warm Period (250-400 AD) and the Medieval Warm Period (950-1250 AD). And, diminished solar activity corresponds equally well with the cooler climate of the “Little Ice Age” (1350-1850 AD).
However, in an effort to prove that only man-made emissions of carbon dioxide drive contemporary global warming, climate activists will sometimes refer to a graph of recent solar activity in order to dispel the notion of solar influence. Specifically, they cite a chart showing the sun and global temperatures moving in “opposite directions” over the past 35 years (see figure A.)
Their argument goes something like this: If solar activity drove climate change, the graph in question should show an exact, continuous correlation between the trajectory of solar activity and global temperatures. But since their trajectories start to diverge, somewhere around 1980, this proves there’s no causal relationship.
Unfortunately, this assumption misses a key point about recent solar activity.
There was a continuing net uptick in solar output from the latter portion of the 1800s, right up through the start of the 2000s. If one scrutinizes Figure A carefully, they’ll note that solar activity essentially plateaued at an incredibly high level from roughly 1950 into the early 2000s. This ongoing, high output helped to drive a continuing climb in temperatures.
More significantly, even accounting for the up-down variations seen since roughly 1960, the overall level has been unprecedented in historic terms (see Figure B.)
And even at the lower level marked for roughly 2010, solar output remained higher than seen in the early 1900s.
Overall, one could say that the sun put the pedal to the floor starting in the late 1800s, and powered a warming trend that lifted global climate out of the troubling cold era of the “Little Ice Age.”
Interestingly, the decline in solar activity at the start of the 2000s coincides rather intriguingly with the observed “pause” in global climate starting around the same time. One could ponder if this might also argue in favor of the overall impact of solar variability.