Warming Before Global Warming Was Not Globally Coherent Warming

Do you remember, back in the good old days, just over a year ago (6 months BC – Before Covid) when the mainstream alarmist media was breathlessly reporting two studies which showed that modern global warming was truly global and unprecedented in magnitude in the last 2000 years? I doubt you could have missed it; news of this alarming and climate-sceptic-shattering discovery was literally everywhere. Raphael Neukom and fellow researchers ‘proved’ (using the ever so reliable Pages2k tree ring and assorted other proxy data) that, not only was man-made global warming the only spatially and temporally coherent warming of the last 2000 years, but that it was also the warmest warming episode over that period. This means of course that the dreaded 20th century AGW is ‘unprecedented and unparalleled’, that mother nature’s past puny attempts to warm the planet were at best patchy and relatively inefficient compared to planes, trains, automobiles and factories. That immense fusion reactor in the sky, 330,000 times the mass of earth, right on our celestial doorstep, plus the vast natural heat engine of the earth, powered by the Sun and animated via oceanic and atmospheric currents spanning the entire globe, just can’t compete with a slightly increased prevalence of the Thermageddon molecule consisting of two oxygen atoms and one carbon. It can’t. We know it can’t because they told us so: it’s settled science.

No evidence for globally coherent warm and cold periods over the preindustrial Common Era

Earth’s climate history is often understood by breaking it down into constituent climatic epochs1. Over the Common Era (the past 2,000 years) these epochs, such as the Little Ice Age2,3,4, have been characterized as having occurred at the same time across extensive spatial scales5. Although the rapid global warming seen in observations over the past 150 years does show nearly global coherence6, the spatiotemporal coherence of climate epochs earlier in the Common Era has yet to be robustly tested. Here we use global palaeoclimate reconstructions for the past 2,000 years, and find no evidence for preindustrial globally coherent cold and warm epochs. In particular, we find that the coldest epoch of the last millennium—the putative Little Ice Age—is most likely to have experienced the coldest temperatures during the fifteenth century in the central and eastern Pacific Ocean, during the seventeenth century in northwestern Europe and southeastern North America, and during the mid-nineteenth century over most of the remaining regions. Furthermore, the spatial coherence that does exist over the preindustrial Common Era is consistent with the spatial coherence of stochastic climatic variability. This lack of spatiotemporal coherence indicates that preindustrial forcing was not sufficient to produce globally synchronous extreme temperatures at multidecadal and centennial timescales. By contrast, we find that the warmest period of the past two millennia occurred during the twentieth century for more than 98 per cent of the globe. This provides strong evidence that anthropogenic global warming is not only unparalleled in terms of absolute temperatures5, but also unprecedented in spatial consistency within the context of the past 2,000 years.

“This lack of spatiotemporal coherence indicates that preindustrial forcing was not sufficient to produce globally synchronous extreme temperatures at multidecadal and centennial timescales.” They don’t have anything to say about climate changes before 2000 years ago, because Pages2k only goes back that far, but the inference is obvious – no preindustrial warming or cooling was a patch on AGW.

Those doughty climate fellows over at Carbon Brief explain why the Roman Warm Period, Mediaeval Warm Period and Little Ice Age were merely sputtering early attempts by nature to change the climate, later to be totally eclipsed by the great climate changing works of Post Industrial Man.

The study finds that no episode of past warming or cooling “shows global coherence in the timing of the coldest or warmest periods”.

For example, during the Little Ice Age, the timing of the lowest temperatures seen in the proxy data varied from place to place.

Two-fifths of the world felt cold temperatures during the mid-nineteenth century, whereas for other regions, the cold snap occurred several centuries earlier, the study says.

And during the Medieval Climate Anomaly, only 40% of the world experienced peak temperatures at the same time, the findings show.

In contrast, human-caused global warming affected 98% of the globe simultaneously at the end of the 20th century, the study says.

Science Daily is at pains to emphasise the ‘fact’ that past climate change was regional:

Climate fluctuations in the past varied from region to region

“It’s true that during the Little Ice Age it was generally colder across the whole world,” explains Raphael Neukom, “but not everywhere at the same time. The peak periods of pre-industrial warm and cold periods occurred at different times in different places.” According to the climate scientist from Bern, the now-debunked hypothesis of climate phases occurring at the same time across the globe came about because of an impression that is defined by the climate history of Europe and North America. In the absence of data from other parts of the earth, this notion was applied to the whole planet, raising expectations that relatively cold or warm periods throughout the last 2,000 years were globally synchronous phenomena. But it has now been shown that this was not the case.

The authors of the study in Nature see the explanation for that as being that regional climates in pre-industrial times were primarily influenced by random fluctuations within the climate systems themselves. External factors such as volcanic eruptions or solar activity were not intense enough to cause markedly warm or cold temperatures across the whole world for decades, or even centuries.

The researchers relied on a database from the international research consortium PAGES, which provides a comprehensive overview of climate data from the last 2,000 years, for their investigation of five pre-industrial climate epochs. In addition to tree rings, it also includes data from ice cores, lake sediments and corals.

It’s clear from this that they only consider that radiative forcing from solar variability or volcanic aerosols, not internal variability, has the potential to change climate on a global scale and that over the past 2000 years, this hasn’t happened because changes in aerosols and solar radiance have been too weak. They thus assign the cause of the RWP, MWP and LIA climate change episodes to internal multidecadal variability which they claim was a regional forcing, not of comparable magnitude to 20th century AGW and not temporally coherent across the globe. Bear that in mind please in the light of new research just published.

An international team of scientists have connected a number of rapid climate change events from the last glacial period in new research that may help future work in climate chronology.

Their findings link 25 major rapid cycles of warming and cooling recorded in Greenland’s ice cores during the last glacial cycle, which occurred 115,000 to 11,700 years ago, to other known climate changes in the Asian Monsoon, South American Monsoon, and parts of Europe and the Mediterranean. Those 25 abrupt changes are known as the Dansgaard-Oschger events, or D-O events.

“Each of these events were characterized by very abrupt warming over Greenland, of up to 16 degrees Celsius, sometimes within decades,” said Ellen Corrick, a researcher at the University of Melbourne and lead author of the study published Thursday in the journal Science. “These warmer conditions lasted for several hundred to several thousands of years before a more gradual cooling occurred.”

Climate change across the globe was synchronous and spatially coherent with the D-O events:

During this period, Corrick said, Europe experienced temperature and rainfall changes in sync with the D-O climate events. The tropics’ monsoon systems also saw changing rainfall patterns associated with the fluctuating temperature over Greenland.

“We found that abrupt climate changes during Dansgaard-Oeschger events occurred simultaneously across a region extending from the Arctic to the southern sub-tropics, within decades in some cases,” Corrick said in an interview. “We have also determined exactly when the abrupt changes occurred, much more precisely than ever before.”

Phys.org says:

Abrupt climate changes during the Last Glacial Period, some 115,000 to 11,700 years ago, happened at the same time across a region extending from the Arctic to the Southern Hemisphere subtropics, new research has revealed.

The study, led by University of Melbourne Ph.D. student Ellen Corrick and published today in the journal, Science, found that rapid warming events over Greenland were linked to simultaneous temperature increases across continental Europe, and changes in rainfall in the Asian and South American monsoon regions.

Greenland ice cores recorded more than 25 abrupt warming episodes during this period. These so called ‘Dansgaard-Oeschger events’ were associated with increases in air temperature over Greenland of up to 16°Celsius, sometimes in a matter of a few decades.

Co-author, University of Melbourne Associate Professor Russell Drysdale, said: “Demonstrating synchrony in the climate response across such a broad region marks a major advance in the study of Dansgaard-Oeschger events. It allows scientists to improve understanding of how the events are propagated globally via the ocean and atmosphere system.

They provide confirmation of a persistent but, until now, unsubstantiated assumption that climate changes between the tropics and the Arctic were synchronous.”

All very well, I hear you say, but what have D-O events during the last Ice Age got to do with the RWP, MWP and LIA?

Wiki, that fount of irrefutable climate knowledge (but seriously, bear with me) says:

DansgaardOeschger events (often abbreviated D–O events) are rapid climate fluctuations that occurred 25 times during the last glacial period.

The comparable climate cyclicity during the Holocene is referred to as Bond events.

The exact cause of D-O events is still a matter of scientific debate but it’s likely that a rapid slowdown of the Atlantic Merdional Overturning Circulation is involved with attendant complex feedbacks in atmospheric circulation.

Although climate scientists have worked hard to determine the ultimate trigger of abrupt climate change during the last ice age, it is likely that a combination of ocean and atmospheric circulation changes were involved. For example, a subtle shift in atmospheric circulation to a more meridional jet stream flow would encourage the transport of warm, salty water into the sub-polar North Atlantic, which in turn could lead to the reestablishment of strong AMOC and enhanced oceanic heat transport to the high-latitude North Atlantic. In this case, ocean circulation changes associated with AMOC may have amplified small changes initiated in the atmosphere on the transition into warm interstadials. Conversely, a sudden reduction in AMOC due to an influx of freshwater into the high-latitude North Atlantic region has the potential to trigger a regional cooling that can significantly alter tropical atmospheric circulation around the globe. Although we still do not know which happened first, interactions between both the ocean and the atmosphere must have played an important role in driving the dramatic climate oscillations of the last ice age. This paper only discusses two hypotheses to explain the abrupt climate shifts of the last ice age.

For our purposes here, we need only note that D-O events are (were) regional fluctuations whose knock-on effects involved synchronous climate change from the Arctic to the subtropics, extending into the southern hemisphere, which may have been forced by internal or external variability, or a combination of both. Given that there were 25 of them throughout the last glacial period, this implies that internal variability of the system may have played a significant part and that some cyclicity was involved. Now, as it happens, D-O events didn’t just go away when the last Ice Age ended; they weakened and became known as Bond Events or abrupt Holocene climate changes, which also happened to manifest as regional climate fluctuations (abrupt warming followed by cooling) which were implicitly connected with AMOC and the North Atlantic. The cool periods are often known as North Atlantic Cold Events and the last one was probably the LIA. There are 9 notable such events at 11.1 kyr, 10.3 kyr, 9.4 kyr, 8.1 kyr, 5.9 kyr, 4.2 kyr, 2.8 kyr, 1.4 kyr, and 0.4 kyr, the last being the LIA minimum, roughly coincident with the Maunder Minimum. The cold events were preceded by warm periods where warming was often rapid, proceeding over the course of decades.

Back in 2003, even climate alarmist Jonathan Overpeck was researching the links between natural abrupt climate changes in the Holocene and the more pronounced abrupt climate changes during the last glacial:

During the last ice age, the Indian Ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial-scale climate events in the North Atlantic region1,2,3, suggesting a mechanistic link. In the Holocene epoch, which had a more stable climate, the amplitude of abrupt changes in North Atlantic climate was much smaller, and it has been unclear whether these changes are related to monsoon variability. Here we present a continuous record of centennial-scale monsoon variability throughout the Holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic Arabian Sea. Our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the North Atlantic region4including the most recent climate changes from the Medieval Warm Period to the Little Ice Age and then to the present. We therefore suggest that the link between North Atlantic climate and the Asian monsoon is a persistent aspect of global climate.

Now, there’s plenty of peer-reviewed studies which, in contrast to Neukom last year, suggest that the LIA/MWP/RWP were in fact global climate events, that they were temporally coherent and that, moreover, they were of comparable magnitude to recent global warming. So let’s ‘follow the inconvenient science’ and see where it leads us. If we do that, it leads us to speculate (with justification, backed up by data and research) that modern global warming, far from being unique, far from being ‘unprecedented and unparalled’ as claimed by Neukom and others a year ago, is just one of a number of abrupt Holocene climate fluctuations mediated via internal cycles operating in the North Atlantic region, connected perhaps to AMOC and maybe also initiated or reinforced by solar variability. The North Atlantic region then is seen to drive global climate change, which is exactly what Tsonis was saying in 2017. This is at least as viable an explanation for a large part or even the majority of late 20th century rapid warming as is GHG emissions. But of course, climate science is not normal science, it’s post normal science, hence alternate, evidence-based explanations for modern global warming must be either ignored or censored.

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via Climate Scepticism


August 21, 2020 at 05:39PM

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