Skeptics of Global Warming (GW) like to point to the Little Ice Age as being caused by the lack of sunspots as evidence of how the sun, more than anything, can affect climate. Covering roughly 400 years and ending around 1650, the Little Ice Age is well documented in studies of glacier advances, ships' logs, and paintings of anomalous winter scenes, among others. Overlapping the Little Ice Age is the Maunder Minimum, a period of decreased sunspot activity that lasted some fifty years, breaking from the traditional 11 year solar cycle. So, hardcore GW deniers will try to convince you that the Maunder Minimum caused the Little Ice Age, explaining that a lack of sunspots means less solar intensity and therefore less heating of the Earth.
While this may be true on its face, they are exaggerating the contribution (or lack thereof) of solar intensity variability with sunspots. And they also conveniently forget that the period of the Little Ice Age was also accompanied by increased volcanic activity which served to veil the Earth in a thin cloud of ash, vastly outweighing the effects of reduced solar activity. Finally, the Maunder Minimum comes at the tail end of the Little Ice Age, so even though it may have contributed in some small way, it certainly did not cause the Little Ice Age.
Now, another contender has entered the arena, vying for its place in history as the cause of the Little Ice Age: the pandemic. Richard Nevle and Dennis Bird of Stanford have examined sediment cores and soil samples dating back 5000 years and noted a precipitous drop in charcoal ash following periods of major pandemics. This indicated a massive decrease in the clearing of forests by burning to create more land for crops. While the population recovered (remember, Europe lost 20-30 million people in the span of six years), abandoned land began to regrow. Whole new forests sprouted, sucking CO2 out of the atmosphere, effectively removing layers from the Earth's thermal blanket. Moreover, their data aligns nearly perfectly (or so they say) with other information (heavy/light carbon isotope ratios) detailing the drop in atmospheric CO2 at the same time.
This is not to say that pandemics are THE cause of the Little Ice Age. Rather, it looks like they are possibly a serious contributor. And, as far as I'm concerned, this holds as much water as the Maunder Minimum correlation. GW deniers have yet to provide a workable theory beyond a few gesticulations as to how the Maunder Minimum could so significantly affect the environment.
See the Standford University News Release for more.