Interglacial, or not interglacial? That is the question.

2.6 million years ago our planet decided that after about 300 million years of warm temperatures it was time to cool things down.  The following chart shows historic temperatures normalized to the average from 1960 to 1990.  When mother Earth decides to cool things down she doesn’t kid around.  The thermostat from 300 to 3 million years ago was set at a significant 2 to 14°C (4-25°F) warmer than today.

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Thus started a period of time geoscientists refer to as the Pleistocene.  The Pleistocene encompasses the most recent long term Earthly temperature reduction colloquially called the “Ice Age”.  An ice age by definition consists of many periods of cold climate called “glacial periods” which are broken up by short lived warm spells we call “interglacials”.  The last interglacial is the Eemian shown above.

The beginning of the end for the Pleistocene is defined as the end of the Last Glacial Maximum (LGM) all the way to the end of the Younger Dryas (YD).  The LGM is the last glacial period with mile thick ice sheets covering most of North America as well as large tracts of Europe and Asia.  It was a 15,000 year long stretch of serious climate upheaval causing global cold snaps, droughts, desertification and frequent dramatic dust laden storms.  The coldest 5,000 year period reached temperatures 5°C (10°F) colder than today and sea levels were up to a 100 metres (328 feet) lower than present day.  Then, 16,000 years ago, temperatures started to dramatically warm.  The warming trend was temporarily interrupted for a 1,000 year break, during the Younger Dryas event which returned the climate to glacial conditions but then the warming returned until about 11,650 years ago when the rapid warming slowed.  The end of this rapid exit from the latest cold period is the marker used to name a new geological epoch called the Holocene.  Since many refer to the Pleistocene as the ice age, the Holocene is inferred to be post ice age.

The temperature chart at the top provides a good presentation of historic temperatures.  However, due to the varying time scales, one may be deceived in perceiving that we have been in a steady temperature plateau that is much longer than any past warm period.

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This chart, which covers the last 450 thousand years, has a constant time scale which provides a correct comparison of the temperature record.  The recent Holocene warming is clearly an event which is very similar to past interglacial periods.  The red values describe the length of the past four interglacials and show how short lived these warming cycles essentially are.  We can also examine the relative temperature of each interglacial pulse and see that we are experiencing similar and possibly slightly cooler temperatures than past interglacials.  The reality is that the Holocene is not post ice age but is likely just another interglacial warming pulse.  Going forward it is more reasonable to expect climate to change as much as it has during the great Pleistocene Ice Age.


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During the Holocene we see that temperatures 8,000 years ago were warmer than present and the variabilities we are experiencing are in line with the past 12,000 years.  There are two significant temperature events that mark the most recent 2,000 years.  The Medieval Warm Period (MWP) from 950 to 1250 AD and the ~550 year Little Ice Age (LIA) from 1300 to 1850 AD are clearly seen.  The MWP with temperatures similar to present day is the reason the Vikings named Greenland as they did and easily colonised much of the North Atlantic including Newfoundland.  The LIA is misnamed; with temperatures approximately 0.6°C (1°F) colder than now it should have been called the Long Cold Snap as it did not drop the ~5° C (9°F) of a true ice age.  No matter how it is named, the prolonged cold caused droughts through much of the Northern Hemisphere with crop failures, famine, social unrest, wars, mass migrations and major disease outbreaks; not a happy time.


In 1976, Hays published the landmark observation that climate records contained the same cycles as are found in the Earth’s orbit around the Sun.  Specifically, they found a dominant ~100,000 year cycle similar to Earth’s orbital eccentricity, a 42,000 year cycle similar to the Earth’s obliquity and a 23,000 year cycle similar to the precession index.  Eccentricity describes the shape of the orbit, obliquity is the tilt of the axis of rotation with respect to the orbital plane and precession refers to the rotational change over time of both the Earth’s rotational axis and orbital path.  They concluded that changes in the orbital geometry are the fundamental cause of ice ages.

In 2010, Akasofu discusses the temperature recovery from the end of the LIA in 1850 AD.  He states that “temperature changes during the 20th century can be approximated by a linear change at the rate of about 0.5°C/100 years”.  Furthermore, he says that solar activity was relatively low during the LIA, but began to recover from about 1800-1850 AD.

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The solar activity Akasofu refers to is the energy ultimately felt here on Earth which is best represented by this Sunspot chart.  We see that during 1300 to 1850 AD the Sun experienced two low stands in activity, the Maunder and Dalton Minimums.  Solar cycle 24 will soon come to an end in early 2019, but we already have enough data to see that it represents the lowest solar activity we have experienced since the early 1900s.

Several scientists have been predicting for some time that our Sun is cooling.  Since 2003 and most recently in 2016 the notable astrophysicist Dr. Abdussamatov, Head of Space Research Laboratory at the Pulkovo Observatory of the Russian Academy of Sciences, has found that the total solar irradiance absorbed by the Earth since 1990 has decreased creating a negative average annual energy balance which will cause long-term adverse thermal condition.  He concludes that “the quasi-centennial epoch of the new Little Ice Age has started at the end of 2015 after the maximum phase of solar cycle 24”.


Furthermore, in 2015 Mörner presented his modelled cooling forecast and predicts that by about 2030 the Sun will experience a new grand solar minimum.  He further says that predictions have extended low activity up to 2160.  In 2015, the science of solar activity prediction took a huge step forward.  Prof. Zharkova’s team from Northumbria University, U.K., have discovered a new modelling approach to capture the dynamo effects found in two layers of the Sun.  Their new technique, when compared to real solar cycle data, found predictions with an accuracy of 97%.  Furthermore, their models also confirm that solar activity will fall by 60% during the 2030s to conditions last seen in the Maunder Minimum.

There is much written by the warming camp that disputes the effect of solar radiance with global temperature fluctuations.  The climate establishment bases these interpretations on an unshakeable faith in their climatic model outputs which tend to discount solar influences.

The IPCC in 2014 forecasted as much as 4.8°C (8.6°F) of warming up to 2100.  They also report: “it is virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas as global mean surface temperature increases.  It is very likely that heat waves will occur with a higher frequency and longer duration” and they don’t stop there, as they claim that climate warming will continue well beyond 2100.

However, the winter of 2018 has been one of the harshest cold snowy winters to hit the Northern Hemisphere for several years.  Is this the beginning of a 100+ year cold snap?  The next decade will be telling.

The scientific method requires that we compare all theories with measured data.  The theory of human caused climate change is failing this requirement.

In science often people refer to Occam’s Razor which simply states that the simplest solution is almost always the best.  In my experience as a geophysicist, I have found that although we look for the simplest solution, more often than not, we discover that the science of the earth is much more complex than we were expecting.  In Mörner’s paper he presents the following chart to explain the “Planetary beat processes and the spectrum of terrestrial variables affected”.  I think it beautifully captures the complexity of our big blue spaceship as we hurtle through the expanse of space.

Climate is changing; let’s stop arguing that anything said here is denying that.  We do need to realize that vilifying CO2 and carbon based energy just to push an agenda of extreme temperature rise without also considering the possible impacts of a cooling world is bad science and poor public policy.  We must evaluate what strategies might best be used in adapting to an under heated planet because cold kills 20 times more people than heat.

In conclusion, if the Holocene is just another interglacial period what are we doing to get ready for the disruption caused by an extended cold snap on the breadbaskets of our planet?

…that clearly is the question!

Andrew Bonvicini, P.Geoph.

1 Comment

  1. Warren Blair

    Excellent analysis of earth history indicating the complexity of climate. The vilification of man made atmospheric CO2 is unjustifiable in view of the myriad of other factors exhibited over earth’s history.

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