How The Arctic Climate Has Changed Since The MWP
By Paul Homewood
We’ve been looking at recent changes in Arctic sea ice extent, but, to put them into perspective, we also need to consider some of the longer term ones.
In this post, I want to discuss how conditions in the Arctic have changed in the last 1000 years or so.
Most of us will probably be familiar with the evidence from Greenland ice cores, which clearly show warmer temperatures than now in the Middle Ages.
There is an abundance of evidence that supports this conclusion. The list is far too long to reproduce here, but there is an excellent summary at CO2 Science here. But the following give some idea:
1) JJ Moore et al’s paper,A 1240-Year Record of Arctic Temperatures, used lake sediment cores from Baffin Island to produce a 1240-year record of average summer temperatures for this region:
As well as the obvious MWP peak, the authors found evidence of large abrupt swings in temperature.
2) Aslak Grinsted et al, Svalbard summer melting, continentality, and sea ice extent from the Lomonosovfonna ice core, found that:
The degree of summer melt was significantly larger during the period 1130–1300 than in the 1990s.
They also note that in addition to summer temperature, the melt proxy also appears to reflect sea ice extent.
3) Catherine La Farge’s study, Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments, has discovered that rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550–1850 AD) on Ellesmere Island.
Carbon dating shows them to be at least 400 years old.
Presently, the Baffin Bay southern sea-ice boundary extends from Disko Island to the southwest, towards Canada. This would imply that prior to AD 1250 this boundary was more northerly and gradually moved towards the vicinity of the core site until after AD 1500 (Little Ice Age), when it was positioned south of the core site.
The other side of the coin to the MWP is, of course, the Little Ice Age, and there is a lot of evidence that this was the coldest period in at least some parts of the Arctic since the end of the Ice Age:
1) Kelly & Long found that the Greenland ice sheet and glaciers reached their maximum extents since the early Holocene during the Little Ice Age.
2) The aforementioned Ribeiro et al found the same.
3) Caseldine’s Study of lichens on Icelandic glaciers reveals that “in all cases the LIA maxima of the glaciers date to the last half of the 19th C, and probably marked the maximum Neoglacial extent of the glaciers”
4) Larsen et al analysed lake sediments, also in Iceland, They found that the LIA contained the most extensive glacial advance of the neoglacial interval, concluding that "the LIA was the coldest period of the last 8 thousand years."
5) Ingolffson et al also studied glaciers in Iceland, finding that most glaciers reached their Holocene maxima during the Little Ice Age (AD 1300–1900).
6) HH Lamb reprints L Koch’s analysis of the occurrence of sea ice at the coasts of Iceland, in Climate History & The Modern World, showing how the climate there change so drastically between the MWP and LIA.
But to really understand the impact, this is how he describes it:
In Iceland the old Norse society and its economy suffered a severe decline which set in first about AD 1200 and could be said to have continued over almost six centuries. The population of the country fell from about 77500, as indicated by the tax records in 1095, to around 72000 in 1311. By 1703 it was nearly down to 50000, and after some severe years of ice and volcanic eruptions in the 1780’s it was only about 38000. The people’s average stature also seems to have declined, much as in Greenland, from 5ft 8in to 5ft 6in from the 10th to the 18thC.
It is clear from the surviving records that years when the Arctic sea ice was close to the Iceland coast for long months (usually between January and August) played a big part in this. In such years, the spring and summer were so cold that there was little hay and thousands of sheep died. The shellfish of the seashore were also destroyed by the ice. Gradually all attempts at grain growing were given up. The glaciers were advancing.
The times of most ice and coldest climate in Iceland seem to have started suddenly in 1197-8 and 1203, and reached culminating phases around 1300, from about 1580 to 1700, especially the 1690’s, and again in the late 18th and 19thC.
Climate History & The Modern World – Page 189
There is clearly nothing unusual about temperatures or sea ice conditions in the Arctic currently, when seen with this wider perspective.
It has been pointed out that, because of orbital changes, the earth should be getting colder and not be as warm as the Middle Ages. Maybe, but is that a good or a bad thing?
I’ll leave the final words to Jørgen Peder Steffensen, Associate Professor at the University of Copenhagen and one of the world’s leading experts on ice cores. Using ice cores from sites in Greenland, he has been able to reconstruct temperatures there for the last 10000 years. So what are his conclusions?
I agree totally we have had a global temperature increase in the 20thC – but an increase from what? ..Probably an increase from the lowest point in the last 10,000 years.
We started to observe meteorology at the coldest point in the last 10,000 years.