Claim: Researchers uncover the surprising cause of the Little Ice Age

Posted: December 16, 2021 by oldbrew in climate, Ocean dynamics, research, Temperature, trees, volcanos
Tags: , ,

A portion of the Atlantic meridional overturning circulation [image credit: R. Curry, Woods Hole Oceanographic Institution @ Wikipedia]

This article starts off confident that the researchers are right – ‘we now know’ etc. – but later retreats and says ‘the cooling appears to have’ etc. But as the Little Ice Age is an interesting topic it’s worth a look.
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New research from the University of Massachusetts Amherst provides a novel answer to one of the persistent questions in historical climatology, environmental history and the earth sciences: what caused the Little Ice Age?

The answer, we now know, is a paradox: warming, says

The Little Ice Age was one of the coldest periods of the past 10,000 years, a period of cooling that was particularly pronounced in the North Atlantic region.

This cold spell, whose precise timeline scholars debate, but which seems to have set in around 600 years ago, was responsible for crop failures, famines and pandemics throughout Europe, resulting in misery and death for millions.

To date, the mechanisms that led to this harsh climate state have remained inconclusive. However, a new paper published recently in Science Advances gives an up-to-date picture of the events that brought about the Little Ice Age. Surprisingly, the cooling appears to have been triggered by an unusually warm episode.

When lead author Francois Lapointe, postdoctoral researcher and lecturer in geosciences at UMass Amherst and Raymond Bradley, distinguished professor in geosciences at UMass Amherst began carefully examining their 3,000-year reconstruction of North Atlantic sea surface temperatures, results of which were published in the Proceedings of the National Academy of Sciences in 2020, they noticed something surprising: a sudden change from very warm conditions in the late 1300s to unprecedented cold conditions in the early 1400s, only 20 years later.

Using many detailed marine records, Lapointe and Bradley discovered that there was an abnormally strong northward transfer of warm water in the late 1300s which peaked around 1380. As a result, the waters south of Greenland and the Nordic Seas became much warmer than usual. “No one has recognized this before,” notes Lapointe.

Normally, there is always a transfer of warm water from the tropics to the arctic. It’s a well-known process called the Atlantic Meridional Overturning Circulation (AMOC), which is like a planetary conveyor belt.

Typically, warm water from the tropics flows north along the coast of Northern Europe, and when it reaches higher latitudes and meets colder arctic waters, it loses heat and becomes denser, causing the water to sink at the bottom of the ocean. This deep-water formation then flows south along the coast of North America and continues on to circulate around the world.

But in the late 1300s, AMOC strengthened significantly, which meant that far more warm water than usual was moving north, which in turn cause rapid arctic ice loss.

Over the course of a few decades in the late 1300s and 1400s, vast amounts of ice were flushed out into the North Atlantic, which not only cooled the North Atlantic waters, but also diluted their saltiness, ultimately causing AMOC to collapse. It is this collapse that then triggered a substantial cooling.

Fast-forward to our own time: between the 1960s and 1980s, we have also seen a rapid strengthening of AMOC, which has been linked with persistently high pressure in the atmosphere over Greenland. Lapointe and Bradley think the same atmospheric situation occurred just prior to the Little Ice Age—but what could have set off that persistent high-pressure event in the 1380s?

The answer, Lapointe discovered, is to be found in trees. Once the researchers compared their findings to a new record of solar activity revealed by radiocarbon isotopes preserved in tree rings, they discovered that unusually high solar activity was recorded in the late 1300s. Such solar activity tends to lead to high atmospheric pressure over Greenland.

At the same time, fewer volcanic eruptions were happening on earth, which means that there was less ash in the air. A “cleaner” atmosphere meant that the planet was more responsive to changes in solar output. “Hence the effect of high solar activity on the atmospheric circulation in the North-Atlantic was particularly strong,” said Lapointe.

Lapointe and Bradley have been wondering whether such an abrupt cooling event could happen again in our age of global climate change. They note that there is now much less arctic sea ice due to global warming, so an event like that in the early 1400s, involving sea ice transport, is unlikely.

Full article here.
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Research article: Little Ice Age abruptly triggered by intrusion of Atlantic waters into the Nordic Seas – Science Advances (2021)

The Little Ice Age (LIA) was one of the coldest periods of the postglacial period in the Northern Hemisphere. Although there is increasing evidence that this time interval was associated with weakening of the subpolar gyre (SPG), the sequence of events that led to its weakened state has yet to be explained. Here, we show that the LIA was preceded by an exceptional intrusion of warm Atlantic water into the Nordic Seas in the late 1300s. The intrusion was a consequence of persistent atmospheric blocking over the North Atlantic, linked to unusually high solar activity. The warmer water led to the breakup of sea ice and calving of tidewater glaciers; weakening of the blocking anomaly in the late 1300s allowed the large volume of ice that had accumulated to be exported into the North Atlantic. This led to a weakening of the SPG, setting the stage for the subsequent LIA.

  1. Coeur de Lion says:

    So there was a Little Ice Age, then. Why hasn’t the corrupt IPCC been challenged publically about its Hockey Stick that adorns the frontispiece of the Summary for Policymakers but does not appear in AR6? But does not have a MWP nor LIA. Do please mine down to the relevant posts in Steve McIntyre’s in order to savior the IPCC’s gross – and incompetent- fraud

  2. […] Claim: Researchers uncover the surprising cause of the Little Ice Age […]

  3. jeremyp99 says:

    Yeah, and the next warming was caused by the cooling yeah?

  4. Saighdear says:

    “Absolutely” just as ‘we now know’ etc. and ‘appears to have’ ….. But when I say that “I Think that ….” I am open to ridicule. …. so, in other words, those “ridiculous” people ‘don’t think’ do they ? Half the trouble with the world. and as for the other half? Speculate.

  5. JB says:

    “No one has recognized this before,”
    “what could have set off that persistent high-pressure event in the 1380s?… solar activity …”

    Such is the state of “modern” science. The most vocal today do not confer with those who’ve gone before.

    An inspection of Long Range’s graphical plot of temperature reveals a cold temperature cycle lasting at least 13K years.What is known about a cycle that lasts that long?

  6. oldbrew says:

    TB – yes, that Ray Bradley…

    Mann et al Northern Hemisphere Millennial Temperature Reconstruction
    Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations

    Michael E. Mann and Raymond S. Bradley
    Department of Geosciences, University of Massachusetts, Amherst, Massachusetts

    Malcom K. Hughes
    Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona

    Published: © 1999, American Geophysical Union

    And that hockeyshtick [sic]…

    Note: temp. anomaly, as stated.

  7. Paul Vaughan says:

    NO point to last

    “No one has recognized this before,”
    fact chuck call$pompUS naiveIT with dull light$now doubt

    “solar activity”
    endlessly repeated misinterpretation (&we no point try yuan diss course sov. no wells$)

    “They note that there is now much less arctic sea ice due to global warming, so an event like that in the early 1400s, involving sea ice transport, is unlikely.”
    actively watched for such a statemeanT …and there IT Was[hi!n’tUN]admitted …at lasst

  8. Paul Vaughan says:

    doesn’t even mention the 6000 years of uncoordinated evil we endure

    let us pray to God for washUN “tune good” tidings

  9. oldbrew says:

    ‘A graphical description of changes in temperature in Greenland from 500 – 1990 based on analysis of the deep ice core from Greenland and some historical events. The annual temperature changes are shown vertical in ˚C.’ – Wikipedia

    See what the chart numbers mean, here:

  10. Scott says:

    Even when we’re wrong, we’re right.

  11. stpaulchuck says:

    so that was the global cooling caused by the global warming, okay, got it [laughs behind hand]

  12. Graeme No.3 says:

    No mention of the previous Dark Age when the Bosphorus froze over (and people could walk from Constantinople to Asia) about 800 A.D. and people in Egypt started wearing furs?
    And apparently no thought that a series of large volcanoes could have reduced sunlight reaching the surface of the Earth (as in the Dark Ages when observers complained that the sun appeared dim and barely cast a person’s shadow on the ground at noon)?

  13. dscott8186 says:

    This reminds me of CNN claiming a car ran over those poor people in Wachasha as though no one was driving. A murderous criminal was driving the car.

    Correlation is not causation, warmth and cooling always follow each other. Notice they didn’t bother to examine other variables occurring at the same time. What’s really going on here is that they know a cooling period is starting and they are trying to deceive the public as to its cause. The money must flow or they become irrelevant.

  14. Phil Salmon says:

    In my view what the authors are describing here is just a powerful excursion of the AMO. This is an excitability driven oscillation in a dissipative open system.

    – more warm water transport to the Arctic via the AMOC first increases downwelling of cooled high density saline water in the Norwegian Sea, self-reinforcing the AMOC.

    – but the warming of the Arctic leads to melted freshwater which chokes off the Norwegian Sea downwelling.

    – so eventually the AMOC slows down and the Arctic cools down again

    – rinse and repeat for as long as an Atlantic Ocean exists.

    The AMO is a chaotic-emergent oscillation which is not a uniform sine wave (very little in nature is). It’s time period is not 60 years but varies from about 30-90 years, as shown by palaeo reconstructions.

  15. Phil Salmon says:

    The unspoken implication?
    That we are right now at the crest of a rollercoaster ride, just about to descend into a sharp cooling trend for a few decades?
    Time will tell.

  16. Paul Vaughan says:

    66 Diss($ov)Course D-forced Framm 96 & 208 = irresponsible + misleading
    ignorance of 96 is a ‘$sure!’ sign of clueless and/or deliberately misleading commentary

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