By Paul Homewood
Booker commented the other day how one scientist claimed last week that we now have “the highest temperatures on Earth since the last ice age”. The BBC failed to even challenge this statement.
This certainly is not the first time I have heard claims (presented as fact) to this effect.
We have already seen concerted attempts to disappear the MWP, so it is time to reclaim the Holocene Optimum (so named for good reason), which is generally accepted to have run from about 9000 to 5000 years ago
Obviously we had no thermometers around in those days, so nobody knows what the average temperature of the Earth was then. There again, nobody really knows now either.
But there is plentiful evidence that many places were significantly warmer than now. I present some of this evidence below, though this is probably only skimming the surface:
1) Greenland
One of the clearest pictures we have is from ice cores in Greenland:
https://notalotofpeopleknowthat.wordpress.com/2017/07/31/shukman-peddles-more-greenland-nonsense/
Not only have temperatures been higher than present for pretty much all of the last 10,000 years prior to the LIA, but the 19thC marked the coldest period of all since the Ice Age, as acknowledged by Jørgen Peder Steffensen, one of the world’s leading experts on ice cores.
Evidence from other sources backs up Steffensen’s findings, for instance:
a) Ribeiro et al.
Analysis of marine sediments in Disko Bay, West Greenland finds that:
a) The past 1500 years have been identified as one of the coldest intervals of the last 7000 years in Disko Bay.
b) This period is inserted in the context of the Neoglacial Advance of the Greenland Ice Sheet starting at c. 5000 years BP and culminating in the Little Ice Age.
c) The late Holocene cooling trend is also consistent with marine and terrestrial records from several records in the N Hemisphere.
b) Kelly & Long
Study of marine shells, moraines etc finds:
a) The Greenland Ice Sheet may have receded tens of kilometers within its present day margins during the early and mid Holocene.
b) This ice sheet recession was likely a response to the warmer temperatures of the Holocene Thermal Maximum (9-5 ka) (e.g., Kaufman et al., 2004), which is registered by Greenland ice cores as ~2.5°C warmer than at present.
c) In many locations the ice sheet and mountain glaciers reached their maximum extents since the early Holocene during the Little Ice Age.
2) Arctic
There is also plenty of evidence of the Holocene Optimum elsewhere in the Arctic:
a) Levac et al
Analysis of sediments in Baffin Bay :
“ From ca. 6400 to ca. 3600 14C yr BP, transfer functions indicate warmer conditions than at present, with SST in August fluctuating up to 5.5°C. After 3600 14C yr BP, the dinocyst record suggests a trend of decreasing temperature toward modern values, marked by recurrent cooling events.”
http://onlinelibrary.wiley.com/doi/10.1002/jqs.614/abstract
b) Larsen et al
From lake sediments in Iceland, they conclude:
a) The Langjokull ice cap began to expand about 5500 years ago.
b) 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."
http://www.co2science.org/articles/V15/N39/C2.php
c) Ingolffson et al
Study of glaciers in Iceland reveals:
a) During the mid-Holocene climate optimum some of the present-day ice caps were probably absent.
b) Ice caps expanded after 6.0–5.0 cal. kyr BP, and most glaciers reached their Holocene maxima during the Little Ice Age (AD 1300–1900).
http://www.sciencedirect.com/science/article/pii/S1571086609013049
d) Koshkarova & Koshkarov
Analysis shows that temperatures in northern Central Siberia were 3 to 9 °C higher in winter and 2 to 6 °C in summer.
e) Fortin & Gajewski
A study of chironomid remains in the sediments central Canadian Arctic showed that summer temperatures were up to 3C higher in the mid-Holocene.
3) North America
https://notalotofpeopleknowthat.wordpress.com/2014/06/22/alpine-tree-lines-offer-clues-to-mwp/
Tree line studies, as reported by HH Lamb are clear evidence of declining temperatures since around 3000BC in the White Mountains of California.
Lamb comments:
Study of the Upper Tree Line on the White Mountains in California, similarly indicates warm season temperatures about 2C higher than today all through the warmest millenia, from before 5500 BC until about 2200 BC.
It was after 2000-1500 BC that most of the present glaciers in the Rocky Mountains south of 57 o N were formed and that major re-advance of those in the Alaskan Rockies first took place.
Significantly Lamb also refers to tree line studies from a variety of regions by Vera Markgraf:
Quoting a study by Markgraf in 1974, which encompassed the Alps, Carpathians, Rockies, Japan, New Guinea, Australia, New Zealand, East Africa and the Andes, Lamb writes :-
Summer temperatures in these regions were 2 C higher than now in the warmest postglacial times (around 5000 BC).
The geographical extent of these findings is particularly significant, and debunks the idea that Holocene warmth was somehow just a regional phenomenon.
4) European Alps
As noted above, tree line studies indicate a much warmer climate, even as recently as the MWP.
Again, Lamb believes that:
“at their subsequent advanced positions – probably around 500 BC as well as between 1650 and 1850 AD – the glaciers in the Alps regained an extent, estimated in the Glockner region, at about 5 times their Bronze Age Minimum, when all the smaller ones had disappeared.”
Lamb’s supposition has been backed up more recently by the discovery of the remains of 4000 year old forests at the leading edge of a Swiss glacier. Dr. Christian Schlüchter, one of the world’s leading experts on geology and paleoclimatology, who made the discovery, stated:
“the region had once been much warmer than today, with “a wild landscape and wide flowing river.”"
the forest line was much higher than it is today; there were hardly any glaciers. Nowhere in the detailed travel accounts from Roman times are glaciers mentioned.”
5) Central Russia
Novenko et al, using pollen and macrofossil evidence in the Don Basin region of Central Russia for the time span ranging from the mid-Atlantic period [7.2-5.7 cal. kyr B.P.] to the present, found:
temperatures during the mid-Atlantic period "were warmer than the present, mainly due to the higher winter temperatures," while noting that mean January temperatures were "about 3-5°C higher than the present climatic conditions." They also state that in the late Atlantic period, "the mean July and the mean annual temperatures rose to about 2°C higher than the present," after which, in the middle and late Subboreal period, they indicate that summer temperatures were "about 1-3°C higher than present values," while noting that that period’s "mean annual temperatures could have been 1-2°C higher."
6) South America
Thompson states that:
Ancient plant beds, radiocarbon dated to 5000 years ago, are being uncovered as the Quelccaya glacier recedes in the Peruvian Andes.
Thompson again,analysing ice cores from another glacier, the Huascarán in the north-central Andes of Peru, found:
“ the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.”
[Also, note the reference to strong warming in the last two centuries – clearly warming 200 years ago had nothing to do with AGW!]
Other research from the Missouri Botanical Garden, which studies tree lines in the Andes, came to similar conclusions:
During the period from 7500 yr BP to ca. 3000 yr BP temperatures rose about 2°C more, causing another upward shift in the forest line of about 300-400 m higher than today, and thereby reducing the area occupied by páramo. Finally, at about 2900 yr BP, there was a noticeable lowering of the temperature that marked the last downward movement of the forest and páramo belts to their present-day positions.
https://notalotofpeopleknowthat.wordpress.com/2014/04/06/we-live-in-cold-times/
7) New Zealand
Figure 2: New Zealand’s estimated mean yearly temperatures since the last ice age. From Fig 5.6 of Ministry for the Environment (1997), based on Salinger (1988).
http://www.niwa.co.nz/our-science/climate/information-and-resources/clivar/pastclimate
NIWA (National Institute for Water & Atmospheric Research) have published the above chart, based on cave speleothems, and commented:
The warmest conditions of the present cycle occurred between 10,000 and 6,000 B.P with temperatures about 1°C above modern values. This warmer climate was mild, with light winds and lush forests.
Last thoughts
These temperature patterns lasted for centuries and more. It is sometimes claimed that recent warming has already offset some of the difference, but the temperature proxies we have for the early Holocene don’t have the fine resolution to detect such short term fluctuations in temperature.
We have, for instance, seen in recent years how much effect ocean cycles, such as PDO and AMO, have on global temperature. Even the 2015/16 El Nino lifted temperatures by nearly half a degree.
There have always been these sort of natural cycles. The average temperatures derived from proxies would in reality have included many ups and downs. In short, comparison of current temperatures calculated over the last couple of decades cannot be meaningfully compared with centuries long trends.
While we don’t have global coverage, what we do know is that in many parts of the world, temperatures in the mid Holocene were significantly higher than in recent decades.
via NOT A LOT OF PEOPLE KNOW THAT
August 19, 2018 at 04:12PM
Iowa Climate Science Education 
4 thoughts on “The Holocene Climate Optimum”