This story is irresistible for a world historian interested in climate change. Richard Nevle, a geochemist at Stanford, argues that the European advent in the New World, which killed 90% of the 80 million native Americans, caused the Little Ice Age.
The native peoples of the New World burned a lot of wood. When they largely didn’t exist anymore, because they suffered high mortality from a host of European diseases to which they had no immunity, they stopped putting carbon dioxide in the atmosphere. Instead, forests grew rapidly since they weren’t being chopped down anymore, and land wasn’t being cleared for agriculture. Forests take in carbon dioxide and exhale oxygen, plus they fix some carbon dioxide in the soil. They are what is called a “carbon sink,” though not a really efficient one, since much of the carbon they take out of the atmosphere eventually finds its way back there. I suspect the dramatic fall-off in the burning of fossil fuels was the much more important cause here.
Less carbon dioxide in the atmosphere reduces the ‘greenhouse effect’ whereby the atmosphere traps heat generated by sunlight and interferes with it radiating back out into space. Mars is so cold because it has a very thin atmosphere and almost no greenhouse effect. But if you get too much carbon dioxide in the atmosphere, it traps quite a lot of heat, and you get Venus, where lead runs in molten streams on the surface. The current dumping of massive amounts of carbon dioxide into the atmosphere by industrial nations is taking us toward the Venus scenario if it remains unchecked.
An alternative theory is that reduced solar activity contributed to the cooling in the 1600s and 1700s. And the warming period of 900-1300 may have already been reversed in part by the Black Death in Europe and the Middle East, which wiped out one third of the population and would have reduced carbon emissions. Of course all these causes could have operated together.
During the Little Ice age in Britain, people used to go ice skating on the Thames in the winter. Agriculture was badly hurt by shorter growing seasons, causing famines and violent competition over resources– i.e. wars and revolutions. Scandinavia, which had been a major player in world affairs during the warm centuries 900-1300– ruling Ireland and Sicily (where Vikings fought Arabs) and discovering North America– rapidly declined in significance as it froze over. The Ottoman Empire, which threatened Central Europe in the late 1500s and early 1600s, began being drained by the need to put down the peasant Celali revolts in the early 1600s in Anatolia, which may have been climate-related. Famously, there were bread famines in France in the 1780s that likely contributed to the outbreak of the French Revolution.
Since the Nile Valley was warmer than Europe (even if less warm in general in this period) and the river inundated its banks annually, providing natural fertilizer, Egypt was a breadbasket of the Ottoman Empire and 15% of its grain probably went to Marseilles in the 1780s and 1790s; the French under Bonaparte may have decided to conquer it in 1798 in part in order to monopolize its grain and so solve the problem of repeated famine in France. In general, the Little Ice Age overlapped with the age of European maritime empires. The impetus for the Portuguese to take the Indian Ocean, for the British to venture to India, for the Dutch to go into what is now Indonesia, may well have been in part to seek new resources at a time of shrinking European crop yields.
I want to underline that climate change was only one of multiple causes in modern history, and sometimes perhaps a minor one. But given that most societies in the early modern period were agricultural, climate has to be taken into account.
The Nevle theory also underlines that human carbon dioxide-spewing activity has already for some time been important in shaping our climate. That organisms have changed the earth’s climate is nothing new. Life forms 2.7 billion years ago began giving us the oxygen in our atmosphere and life has been one reason the earth did not meet Venus’s torrid fate. Ironically, the modern human romance with hydrocarbon fuels now threatens this 2 and a half billion year old success story and is setting us on a slippery slope toward, ultimately, a Venusian hell.