[timschmidt]

1100AD lines up well with the https://en.wikipedia.org/wiki/Norse_colonization_of_North_Am...

It's not my paper, and I'm not a climate scientist, just found it interesting myself. This except was striking:

"According to the study, a spike in plant life was responsible for up to 67 per cent of a significant drop in carbon dioxide levels between 1520 and 1610. Carbon had been transferred from the atmosphere to the land surface through photosynthesis.

Previously cored Antarctic ice samples were investigated. Researchers observed that 7.4 petagrams — or 7-billion metric tonnes — of carbon had suddenly disappeared at that point in time."

[nostrademons]

The Norse colonization doesn't line up well with the Native American disease die-off, though. The Norse colonization didn't seem to have a major impact on major agricultural populations in North America, perhaps because they landed in remote regions of Greenland and Canada with low population densities. The Aztec empire didn't get started until 1372, for example, and peaked entirely during this time of dropping temperatures. Smallpox wasn't introduced until 1519.

I found some independent validation of the drop in CO2 that you cite [1], but the authors have no idea what the root cause was. Possibly the Native American hypothesis could fit as cause for a secondary climate trend from 1600-1800, but it seems like a stretch. Also should not discount the possibility of plant growth feedback loops: it's known that higher CO2 concentrations cause rapid plant growth, and possible that lower solar irradiation might encourage plants to grow more rapidly to capture more of the available solar energy, and both of those lead to the observed drops in CO2 and increased vegetation. Perhaps the causality was that lower solar output -> increased plant growth -> CO2 drop as well as lower solar output -> it's cold and CO2 drop -> it's cold.

[1] https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/201...

[rufus_foreman]

>> The Norse colonization didn't seem to have a major impact on major agricultural populations in North America, perhaps because they landed in remote regions of Greenland and Canada with low population densities

The Norse didn't travel to North America directly from Europe. For them to spread smallpox, someone from Europe would have had to travel to Greenland shortly before they left for North America. Then they would have had to come into close contact with Indians before the disease ran its course among the crew, which, given the close contact on a small sailing vessel, probably wouldn't take long.

[timschmidt]

"There is evidence of Norse trade with the natives (called the Skrælingjar by the Norse). The Norse would have encountered both Native Americans (the Beothuk, related to the Algonquin) and the Thule, the ancestors of the Inuit. The Dorset had withdrawn from Greenland before the Norse settlement of the island. Items such as comb fragments, pieces of iron cooking utensils and chisels, chess pieces, ship rivets, carpenter's planes, and oaken ship fragments used in Inuit boats have been found far beyond the traditional range of Norse colonization. A small ivory statue that appears to represent a European has also been found among the ruins of an Inuit community house.[13]"

From: https://en.wikipedia.org/wiki/Norse_colonization_of_North_Am...

[aetherson]

The Norse had no major impact on North America, certainly nothing even remotely close to causing major worldwide temperature changes. They had like a few seasonal outposts, plus Greenland.