[nostrademons]

This is a fascinating hypothesis, but the timelines don't really add up. Global temperatures started decreasing around 1100 AD, and by 1300 AD the decline was very much apparent [1]. The Little Ice Age temperature low does correspond with the period from roughly 1420-1820, but by 1492 average temperatures were already close to their lows and a full ~0.3C lower than the High Middle Ages. If it were caused by the colonization of the Americas, you'd expect the temperature decline to not start until first contact with the Native Americans.

I think it's more likely that the Little Ice Age was caused by a drop of solar output, and that all of the turmoil in Europe (Black Death, Hundred Years War, War of the Roses, Wars of Religion) that led to the eventual colonization of the Americas was a consequence of resource scarcity in Europe.

[1] https://en.wikipedia.org/wiki/Little_Ice_Age#/media/File:200...

[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.

[genewitch]

a third of a degree Celsius different in 1492, 3 centuries years before Celsius developed that scale, 2 centuries before "a temperature reading device" was even plausible.

~70 years ago, schoolchildren were chastised for commenting that the continents looked like they ought fit together. These children are the ones you're trying to convince, after changing your collective minds at least twice, that there is climate change. Shortly after they were vindicated about the patterns in coastlines they observed, "science" said there was a risk from global cooling. Spock even did an hour long TV show about global cooling and the risks (70s.) Then in the 90s, global warming was heating up, we're all going to die! Now it's neither cooling nor warming (right?), it's just "climate change" and no matter what, we can say "climate change did that". Crazy storms - climate change. Droughts - climate change. Hot summer - climate change. below average winter - climate change.

Now you got "solar eclipse - climate change"; "earthquake in NY - climate change". These are the people you need to convince.

I don't see the point in arguing. My power is hydroelectric, i don't buy disposable stuff if i can avoid it. I have no control over the petrochemical industry - not in the US, not in China. What i do see the point in is calling out silliness like "0.3C in 14XX" and the lies by omission of things like storms that are affected by the el nino/la nina ocean patterns, as well as certain dust events.

I used to link some articles published by NASA/NOAA when these sort of discussions would appear in my peer group. People would refute by linking other NASA/NOAA articles. None of them saw my point, which i think is funny. By the way, you can do the same thing with pubmed articles, if you're ever feeling frisky.