Comprehensive compilation of pre-historic temperature records shows that global warming is reaching levels not seen for at least 6,000 years
NORTHERN ARIZONA UNIVERSITY
Over the past 150 years, global warming has more than undone the global cooling that occurred over the past six millennia, according to a major study published June 30 in Nature Research’s Scientific Data, “Holocene global mean surface temperature, a multi-method reconstruction approach.” The findings show that the millennial-scale global cooling began approximately 6,500 years ago when the long-term average global temperature topped out at around 0.7°C warmer than the mid-19th century. Since then, accelerating greenhouse gas emissions have contributed to global average temperatures that are now surpassing 1°C above the mid-19th century.
Four researchers of Northern Arizona University’s School of Earth and Sustainability (SES) led the study, with Regents’ professor Darrell Kaufman as lead author and associate professor Nicholas McKay as co-author, along with assistant research professors Cody Routson and Michael Erb. The team worked in collaboration with scientists from research institutions all over the world to reconstruct the global average temperature over the Holocene Epoch–the period following the Ice Age and beginning about 12,000 years ago.
“Before global warming, there was global cooling,” said Kaufman. “Previous work has shown convincingly that the world naturally and slowly cooled for at least 1,000 years prior to the middle of the 19th century, when the global average temperature reversed course along with the build-up of greenhouse gases. This study, based on a major new compilation of previously published paleoclimate data, combined with new statistical analyses, shows more confidently than ever that the millennial-scale global cooling began approximately 6,500 years ago.”
Earlier this year, an international group of 93 paleoclimate scientists from 23 countries–also led by Kaufman, McKay, Routson and Erb–published the most comprehensive set of paleoclimate data ever compiled for the past 12,000 years, compressing 1,319 data records based on samples taken from 679 sites globally. At each site, researchers analyzed ecological, geochemical and biophysical evidence from both marine and terrestrial archives, such as lake deposits, marine sediments, peat and glacier ice, to infer past temperature changes. Countless scientists working around the world over many decades conducted the basic research contributing to the global database.
“The rate of cooling that followed the peak warmth was subtle, only around 0.1°C per 1,000 years. This cooling seems to be driven by slow cycles in the Earth’s orbit, which reduced the amount of summer sunlight in the Northern Hemisphere, culminating in the ‘Little Ice Age’ of recent centuries,” said Erb, who analyzed the temperature reconstructions.
Since the mid-19th century, global warming has climbed to about 1°C, suggesting that the global average temperature of the last decade (2010-2019) was warmer than anytime during the present post-glacial period.
McKay, who developed some of the statistical approaches to synthesizing data from around the world, notes that individual decades are not resolved in the 12,000-year-long temperature reconstruction, making it difficult to compare it with any recent decade. “On the other hand, this past decade was likely cooler than what the average temperatures will be for the rest of this century and beyond, which are very likely to continue to exceed 1°C above pre-industrial temperatures,” McKay said.
“It’s possible,” Kaufman said, “that the last time the sustained average global temperature was 1°C above the 19th century was prior to the last Ice Age, back around 125,000 years ago when sea level was around 20 feet higher than today.”
“Investigating the patterns of natural temperature changes over space and time helps us understand and quantify the processes that cause climate to change, which is important as we prepare for the full range of future climate changes due to both human and natural causes,” said Routson. He used an earlier version of the database to link Arctic warming to a reduction in precipitation at mid latitudes (see related article).
“Our future climate will largely depend on the influence of human factors, especially the build-up of greenhouse gases. However, future climate will also be influenced by natural factors, and it will be complicated by the natural variability within the climate system. Future projections of climate change will be improved by better accounting for both anthropogenic and natural factors,” he said.
The reconstruction of past global temperature is the outgrowth of several NAU research projects aimed at understanding the causes and effects of natural climate variability, work that was funded through more than $1.2 million in grants from the National Science Foundation. The team was recently awarded another $678,000 in grants from the NSF for related work extending through 2023.
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“The reconstruction of past global temperature is the outgrowth of several NAU research projects aimed at understanding the causes and effects of natural climate variability, work that was funded through more than $1.2 million in grants from the National Science Foundation. The team was recently awarded another $678,000 in grants from the NSF for related work extending through 2023.”
I hope they produce lots more pretty graphics, because that’s a lot of money for just one.
I note not one of the climate alarmists have answered my very simple earlier question.
Does the increase they see take us closer to or away from their ideal Earth temp?
Also would they tell us what their ideal Earth temperature is?
It is not a difficult question is it? After the $billions spent thus far on climate research surely one of the scientists can tell us what temperature are they hoping to maintain?
Just asking.
The graph clearly shows Mann-made warming.
Assume that this is true.
Is this a good thing or a bad thing?
Warmer is better.
Well it’s Mann-made, so mostly bad and deliberately so, to exaggerate the warming.
“Before global warming, there was global cooling,”
and before global cooling, there was global warming.
Why is the warming from 12000 years to 6500 years before 1950 not explained?
What was the reason for this warming?
It must have been the “Troglodyte greenhouse effect”. /sarc
Why is 1950 the launch mark? Anybody know?
I think it has to do with WWII. See you can’t claim that humans were the scourge of the Earth during world war periods–that’s just “not done”. So it has to be after the wars, because the war years are sacred. For that matter, what about Victorian times to pre-1950? Lots of factories, lots of emissions–just not a whole lot of cars.
So why 1950? I mean what is it before then that stops them? Television? Big cars? Massive factories producing every “modern” convenience? Is that it? Is that why 1950 is the stopping point? On Dec. 31, 1949 did all these massive factories and cars just suddenly start at the stroke of Jan 1, 1950 at 12:01 am or something?
I’m sure there is a mountain of temperature data during WWII, but for some reason, we never hear about it…imagine that. Furthermore, I’d argue that there is massive temperature data from WWI and before that as well.
Notice the left side of the graph. Time frame 1800-1900. That is not just cherry picking, it is a full cherry pie.
Thanks to the post war economic booms, 1950 is when CO2 levels started growing dramatically.
1950 is the year zero in the Before Present time scale because it was initially based on radiocarbon dating, and radiocarbon dating stopped being precise in the early 1950s due to atomic bomb atmospheric testing that introduced a huge deviation.
Most climate proxies do not reach the present because they are based on sedimentary processes that require a compaction produced by more sediments on top. An example are ice cores where the snow has to be compacted into ice by a process of firning.
There wasn’t enough stuff dumped into the atmosphere by atmospheric atomic bombs to affect radio carbon dating.
What messed up radio carbon dating was millions of tons of ancient carbon being dumped into the atmosphere as CO2 from burning massive amounts of nat gas, oil and coal. Between 1650 and 1950, radio carbon data became problematic. As long as your sample was from a place well away from where coal was being burned, you were probably OK.
I guess you don’t know what you are talking about and are giving just your opinion.
“The Beta-counting method detects the rate at which purified carbon decays. As W.F. Libby determined, one gram of pure carbon should produce about 14 (13.56) radioactive decays per minute.
14C => 14N + β
A rate of 7 decays/gram/minute would indicate an age of one half-life, or 5730 years old. 3.5 decays/gram/minute of carbon would be produced by a sample 11,460 years old.
However, atmospheric testing of nuclear weapons in the late 1950’s and early 1960’s greatly increased the amount of radiocarbon in the atmosphere, so the decay rate of 14 decays per minute more than doubled. Therefore, radiocarbon dates are calculated to a “pre-bomb” age of 1950 A.D. Material which died after 1950 has such high amounts of radiocarbon its age is reported as “percent modern (1950)” (example 180% modern). This bomb radiocarbon has been gradually removed from the atmosphere by by natural processes, but the “bomb spike” can be shown through the dating by means such as comparing the bottle date and radiocarbon age of wines.”
https://www.geo.arizona.edu/Antevs/ecol438/radiocarbon.html
Given the half life of CO2 in the atmosphere is only 5 to 10 years, there isn’t much left from the atom bomb tests.
So the dumping of millions of tons of ancient CO2 into the atmosphere had less impact than a couple of a-bombs?
It had a different impact. You have to consider that 14C amount is very, very small compared to 12C. Atomic tests increased 14C (the numerator) and thus had a huge impact on that ratio.
Fossil CO2 is a small part of total atmospheric CO2 that also fluxes into oceans and the biosphere. To affect the 14C/12C ratio, fossil carbon is affecting the denominator that is very large, so its impact on the ratio is much smaller.
Atomic tests had an acute large effect and since they stopped, they produced a spike that is permanently registered on the remains of all living things at the time. If you produced your teeth in the late 50s to 70s, the spike is permanently registered in them.
Fossil fuel burning produced the Suess effect, a progressive reduction in the 14C/12C atmospheric ratio. It is small (1-2%) but it could be detected already in 1979 and requires a small correction in recent samples. But it is estimated than in a few decades it might reverse the Δ14C difference between the atmosphere and other reservoirs, leading to a reversal of the radiocarbon clock.
Has nobody read the most important sentences in the end of the paper?
“Our reconstruction, which is based on much more proxy data and multiple statistical methods, reinforces the mismatch between higher-than-pre-industrial GMST as represented by the proxy data versus the lower-than-pre-industrial GMST as simulated by climate models.”
This implies that climate models up to now aren’t able to reconstruct the GMST of the holocene as they were reconstructed. However, they are able to simulate the future 🙂 .
The Holocene Temperature Conundrum is alive and well.
It can only be resolved by ditching models or ditching climate proxies, whatever.
Paleoclimatology has never supported well the dogma. Many paleoclimatologists are skeptical and entertain all kind of heretical notions, like it could be the Sun. But the orthodoxy is already hard at work. Through the PAGES Consortium and their inquisition tactics they are rewriting the distant past, and everything that disagrees will be disavowed. Careers are at stake and only retired professors dare to speak up, but they can be safely ignored on account of senility.
Ditch the idea that a global average matters.
Welcome back Javier!
I agree about PAGES, it’s criminal vandalism of palaeo climate data. Palaeo climate data are NOT safe in the hands of the current generation of activist place-holder “scientists”. Steve MacIntyre has exposed the pure fraud at work in the PAGES palaeo-ironing-board.
According to that chart, we are only a few tenths of a degree cooler than the height of the holocene optimum.
Boy, have they cooked the books.
Did Mann have a part in this study?
This contributes little to nothing to what we already knew about our interglacial and ECS of increased CO2. Holocene optimum was 8K years ago and we have been cooling ever since heading to the next glacial period, we already knew that. ECS at a maximum of 1.4C makes their estimate of 1C warming a non-discovery. If we have managed to push off the onset of the next glacial period for a few hundred years, I am all for it. I mean I like my Canadian cousins but having to put up with them for 50K years while their country is covered in ice is a bit much
From the article: “Over the past 150 years, global warming has more than undone the global cooling that occurred over the past six millennia, according to a major study published June 30 in Nature Research’s Scientific Data”
Wrong! Global warming has not even undone the warming that occurred during the Early Twentieth Century much less the last 6500 years.
Here are (below) unmodified (actual temperature readings) Tmax surface temperature charts from all over the world that show it was just as warm in the Early Twentieth Century as it is today. And it was even warmer in the Midieval Warm Period and the Roman Warm period.
These “climate scientists” are ignoring the data right in front of their eyes.
Tmax charts
US chart:
China chart:
India chart:
Norway chart:
Australia chart:
Is anyone really surprised that the “School of Earth and Sustainability” has come up with anything less than a complete CAGW Orthodoxy result?
Joel–“Climate Dowser”
Good one.
Belief in dowsing goes away back. In the 1550s it was used to discover water and silver.
Georges Bauer under the name of Agricola wrote “De Re Metallica” . Published in 1556 it was THE book on mining and metallurgy for at least 200 years.
Bauer debunked dowsing.
Now to this article.
Clearly, “they” have extended the handle of the Hockey Stick from 1,000 years to 6,000 years.
Not just an ordinary scam, but one exaggerated by orders of magnitude.
The actual consensus is that the Holocene thermal Optimum was 2 C+ warmer than now for 4,000 years. Revisionist history appears to be the dominate paradigm now.
The Little Ice Age peaked in the late 1600s and that’s when our current warming cycle started. It’s easy to verify but it’s off message because CO2 couldn’t have been the cause so 1850 is used instead.
Most climate sceptics I know don’t realise this.
What’s the reason for the blue squiggly line going from year 0 to 1950?
The sea level was 1-2 meters higher 6500 years ago.
Since it’s natural, who cares?
Paper finds solar activity at end of 20th century was at highest levels of past 9,000 years
I just can’t take any study seriously that claims a confidence interval of what looks like one degree C using solely smoothed proxies. I can’t see any way the actual confidence interval could be less than 2 degrees, and quite possibly 4 degrees.
The study served up its purpose.
$1.2 mil of public money then 50% to keep going as there is not enough alarmism any more
This is the same palaeoclimate stir-fry approach as used by Shakun and Marcott.
An easy recipe – mix in as many proxies as possible with no selection as to quality. Stir thoroughly until any past changes in temperature are ironed flat.
Result – recent warming looks exceptional, hockey stick delivered. The job’s a good-un.
Steve McIntyre had the method diagnosed probably 10 years ago.
Assemble a bunch so-called proxy time series that are indistinguishable from random noise.
Stir in a few more proxies one might find that just happen to have a recent uptick.
And, mirabile dictu, they combine to produce a flat handle and a hockey stick blade.
All the supposed conformations of Mann’s hockey stick employed that sure-fire method. As Steve McIntyre exhaustively documented.