From NASA - volcanic vs solar activity: https://pubs.giss.nasa.gov/abs/st07500u.html https://pubs.giss.nasa.gov/abs/st07500u.html "volcanos erupted causing a c

From NASA - volcanic vs solar activity: https://pubs.giss.nasa.gov/abs/st07500u.html https://pubs.giss.nasa.gov/abs/st07500u.html "volcanos erupted causing a cold period that lasted from the 1600s to the late 1800s" Correlation vs causation - while the volcanic winter phenomenon is well-known, there are those that propose that solar activity is the primary driver of climate on Earth: https://www.amazon.com/Neglected-Sun-Precludes-Catastrophe-Independent/dp/1909022241 https://www.amazon.com/Neglected-Sun-Precludes-Catastrophe-I... http://www.breitbart.com/big-government/2016/08/12/winter-is-coming-warns-the-solar-physicist-the-alarmists-tried-to-silence/ http://www.breitbart.com/big-government/2016/08/12/winter-is... Not to say that the greenhouse effect is not real, or that anthropogenic CO2 does not cause warming - just that the magnitude of the effect may well be greatly over-hyped.