I caught a few interesting snippets on a science programme on Radio 4 this afternoon. After smallpox reduced the population of Central and South America from circa 60 million down to circa 10 million, there was a measurable drop in the global level of CO2. This led to the lowest temperatures during the mini ice age when the Thames froze over.

Then they think the reason that the Vikings abandoned Greenland was down to a rise in the sea level by some 3.5m, due to the ice cap increasing and the weight of it causing the land to drop. This also led to increased tidal rises, so a combination of the two saw a loss of farmable land etc.

Fascinating stuff for me anyway!

I am not sure I understand the logic there Steve.

If the Greenland Ice Cap increased in size (weight) then surely the lower lying coastal areas (in the south) would have risen up? Although such movements take a long time really take effect - look at what is still happening in the UK - with Scotland rising and southern England sinking millennia after the Scottish ice caps have melted.
 
But such an effect would have increased the above sea landmass, not diminished it surely? Plus as the Ice Caps grew in size, sea level would have fallen, again increasing the above sea level landmass. However, that land may have been of no value to the Viking settlers, as the overall land temperature would have dropped due to the growing glaciers on land and the sea-ice around the coasts. So whilst there was more land it was not capable of sustaining crops or herds.

Whilst I'd previously read that the dramatic and sudden population loss in Central (& South America) had a significant climate impact, there is a theory that the devastation of the Mongol Conquests created a similar climate change, that resulted in some long and very hard winters in the C13th - particularly in Eastern and Central Europe.

Likewise, there have been recent aerial LIDAR scans made in the Amazon, that seem to indicate there were once massive cities in what is now the jungle. These cities seem to have had large agricultural areas around them. The emerging academic view is that they may well have disappeared (for some unknown reason) around the time of the Fall of the Roman Empire - when we have written reports of shorter summers, cold and very rainy weather and overcast skies. But equally, there is a counter view that both the Fall of Western Roman Empire and the abandonment of the Amazonian cities, might have been caused by a massive volcanic explosion in Indonesia.

But all very interesting stuff ... clime catastrophes, man made or natural seem to have a huge impact on our history.

The Greenland bit I did find a tad hard to follow, but I was being distracted at the time. There was mention of a local gravitational effect (IIRC) that increased the sea level, but somewhat over my head as to how this would actually happen.

Quote from: Steve J on 21 April 2023, 06:05:24 AMThe Greenland bit I did find a tad hard to follow, but I was being distracted at the time. There was mention of a local gravitational effect (IIRC) that increased the sea level, but somewhat over my head as to how this would actually happen.

Blimey ... a shift in the North Pole maybe? It has happened many times in earths history apparently. But I am not sure that would have effected the temperature, as that is dependent upon the angle of the earths axis towards the sun.
But Western Europe did also experiance a mini ice age at about the time of the Spanish Conquests - as witnessed by some of the Dutch old master paintings of frozen rivers and canals - and the famous Frost Fairs of London over 100 years later.

I do wonder if the whole Viking Greenland settlement was pretty much always doomed - if you look at the numbers of people a standard Viking long-distance ship could carry you'd need a lot of them to deliver even a reasonable number of colonists to Greenland from Denmark. If you then factor in the historic mortality rate, the exceptional harshness of the local climate, it's probably no-wonder the settlements died out.

The other theory on Greenland is that the Viking 'discovered' and settled it during a period of global warming and that the disappearance of the settlements coincided with the return to more a 'normal' Greenland climate.

But all very interesting stuff. I'll have to look out for the program.
Thanks

It was 'Inside Science' IIRC, but was on 4.30pm yesterday, if you want to catch up on it.

I heard the same programme and it did say that the ice made the land sink.  There wasn't much explanation though.

The weight of the ice makes the land below sink.

If sufficient ice accumulates at the poles and in glaciers or on mountain tops, etc. sea level also sinks.

"Solid earth" is far from solid

When I did Earth Science at uni we were told that an Ice Age was any period in which there was permanent ice at the poles and that we were therefore still in the Quaternary Ice Age ... a premise not universally accepted even then, I believe.

We were also taught that, at the time, new-fangled tectonic plate theory. 

Post Glacial rebound
https://en.wikipedia.org/wiki/Post-glacial_rebound
The Norwegians have a folk tale of Thor being tricked in a drinking contest and drinking the sea causing the sea level to drop tale. This is folk memory of sea level change, backed up by fossil barnicales universally round the Norwegian coast at a much higher than high tide level, which is caused by Norway 'bouncing' upwards after the glaciers receeded and this also caused a massive tsunami 9The Storegga slide) on the east coast of Britain!
https://sciencenorway.no/earth-forskningno-geological-mapping/norway-is-on-the-rebound---and-getting-higher/1394524

https://www.lifeinnorway.net/storegga-slide/

QuoteWe were also taught that, at the time, new-fangled tectonic plate theory. 

Everything I know about plate tectonics I learnt from In Our Time. Interesting stuff.

Early 80s, I was Environmental Studies Graduate... not a good one. Climate change... and it's effects... were 'contested' issues in 'accademia'. One view was that we were about to enter a new 'ice age'... the other, that it would get warmer. 
Effects of either... too many to list. Climate change extremely complex and they were just starting to puzzle things out, then.
Climate has cycles... several of them...from 'short'term to Very long... and they interact.
'Events'... whether natural cataclysms, or man made... are 'blips' in the pretty much unstoppable processes going on in the world. 

Have seen sea fossils near me on Worsaw Hill at the back of Pendle Hill, only 725' ASL

https://thejournalofantiquities.com/2016/07/01/worsaw-hill-burial-mound-near-downham-lancashire/

the land certainly gets moved about a bit!

Isostatic Rebound is the last trump card in the climate chaos lexicon - the ice melt on Greenland & Antarctica is so fast (geologically speaking) that the land may well 'snap' back up and cause massive tears in the joins between tectonic plates, whose joints are more lubricated by warmer ocean water, thus increasing the risk.