Carbon dioxide and temperature are linked. 1650 was the height of the Little Ice Age [0]. Lots of interesting theories and research, e.g. [1], for the specific carbon dioxide drop.
The link from CO2 to temperature is well discussed. But carbon does not randomly disappear from the atmosphere, so either the trigger must have been something on the ground/at sea or there's also a reverse causal link from temperature to CO2 (so it could be triggered by something sun activity), which would imply a terribly unstable system. A very interesting topic indeed. Could variations in the amount of living biomass (which temporarily binds carbon to be released after death unless buried into isolation) make that much of a dent in atmospheric carbon concentration? My gut feeling says atmospheric carbon far outweighs biologically bound (and is in turn dwarfed by geologically bound, until we have dug it all up), but that's really just a guess.
[0] https://en.wikipedia.org/wiki/Little_Ice_Age
[1] https://www.nature.com/articles/ngeo2769