Asking a Physicist About the Little Ice Age

by JoHarrington

What caused the Little Ice Age? Was it really demonic Alpine glaciers, or the volcanos? Liam Dodd from Swansea University reviews the theories.

Between the 13th and 19th centuries, the world froze. Great storms took out parts of Germany and the Netherlands. The Hudson River grew an icy bridge; while fairs were held on the frozen River Thames. Hundreds of thousands of people died.

So what caused it and could it happen again? I grabbed the nearest physicist and put my questions to him. Though it should be disclaimed that Liam Dodd is not a climatologist. His field of research is all about black holes. "Could the Little Ice Age have been caused by a black hole?" I asked him.

"Probably not." He replied. "At least, it's statistically unlikely." Better find out what did then!

Was it Actually an Ice Age?

As I was researching the history of the Little Ice Age, I kept coming across commentators who denied that it was one at all.

According to those detractors, there should be more glaciers in a genuine ice age. 

The last big one, which melted 10,000 years ago, left a sheet of ice a mile high over much of northern Europe, America and Asia.  That was conspicuously missing during the Little Ice Age.  Unless you happened to be in Greenland at the time.

After assuring Liam I'd make certain that all readers know he can only answer questions in general Physics terms (unless black holes crop up), then this was my first query. Was the Little Ice Age really an ice age?

"The IPCC does consider it to be an ice age."  He told me. 

"Who are the IPCC and why should we trust them?"

"The Intergovernmental Panel on Climate Change."  He waited for me to have heard of them, before adding, "The world's leading experts on the climate."

"Do you trust their word?"

Liam laughed.  "Yes."

"Then I do too."  It was an ice age.

Think about the Ice Age and your mind may conjure up images of mammoths and glaciers covering Northern Europe. But we've not long come out of one.
The Little Ice Age was a time of climate related catastrophe on a global scale. The medieval world suffered for 500 years under it. The History Channel tells the story.

The Sea Level Rose During the Little Ice Age

Glaciers growing, glaciers shrinking, oceans rising and falling. What's going on here?!

Image by Rita WillaertMy next question came from a reader.  Ragtimelil read what I had to say about the history of the Little Ice Age and asked, 'If the ocean level is rising due to melting ice, why did the levels rise during the ice age?'

Liam explained that much depends upon where glacial activity is taking place. 

The Arctic can deposit all the ice that it wants to into the ocean, and it won't make a difference.  There the glaciers float on the water, so it's simply a matter of swopping ice for seawater. 

The problems begin when the Antarctic glaciers start melting.  They sit on land, so that water has to drain off into the ocean.  That's what raises sea levels.

During the Great Ice Ages, the sea levels were much lower, because of all the water bound up in ice.  But the opposite was true of the Little Ice Age.  The former affected the South Pole; the latter only the North Pole.

He added that it's quite unusual, in the vast scheme of things, for our planet to have glaciers on its poles.

The Physics of the Little Ice Age - Century by Century

For half a millennium, temperatures dropped and the weather fluctuated through extremes. What on Earth was going on there?

Let me reiterate here that Liam Dodd is not an expert in this period of history.  He's a very good Physicist, but his expertise is largely due to information that I fed him about the conditions, plus some statistics that he was able to dig up.

It's a great overview, but he's careful to tell me that we have to dig deeper for the most up to date and precisely informed thinking in the field.  Academics.  Always covering their backs.

(And for the record, I trust his opinion on this stuff.)

From about 1250, and throughout the rest of the 13th and 14th centuries, temperatures began to drop.  Glaciers crept forward and heavy rain destroyed crops throughout Northern Europe, America and Asia.  Thousands died in famines, especially between 1315-17.  So what had Physics done to us, Liam?

"The reason that it rained a lot is that the cold front was screwed up, due to the encroaching glaciers. This caused the climate cycle to be off.  As the cold front advanced, there was much more stormy weather.  It was hitting the warm front in places where it hadn't before."

By the 15th century, the weather was swinging through extremes. One year would see everyone shivering in the cold all year round, buffeted by terrible storms and unseasonal snow.  The following year would be a heatwave.

Liam had a stark warning, even more unsettling than those weather conditions.  "What happened then is what is going to happen to us soon."  Undeterred by my alarm, he plunged on. "The shifting weather systems caused large variables.  The whole weather system was being knocked out of play."

"So it was like a pendulum?"  I asked.  "The weather swinging around trying to find something it liked?"

"No.  One variable would cause the next."  Liam informed me, in a tone of voice which discouraged thinking of the weather as something sentient.  "It was a positive feedback loop, whereby each climatic event would push the next even further out of whack.  The weather patterns kept changing, because that cold front was colliding with the warm front ever further south."

Positive and Negative Feedback Loops in Climate

This is how Brian Jones, of Colorado University, explains the effects of feedback loops to children.

So a small shift in the weather cycles, around the North Atlantic region, in 1250 had started to escalate off the scale. 

By now, the positive feedback loop meant that the weather systems were becoming increasingly erratic.  That not only explained the back and forth extremes in conditions during the 15th century, but set up the planet for what was to happen next.

Academics of all subjects agree that 1550 was when the Little Ice Age really kicked off.  By now, Liam had his own statistics to support what I was telling him about the history.  He wished to draw our attention to the CO2 levels between 1550 and 1600.

"From 1550, they show that the planet got colder rapidly.  This was still the positive feedback loop in action.  It just kept on getting colder." 

The frankly terrifying graph below demonstrates this perfectly.  Until the end of the 11th century, the levels of CO2 were rising steadily, then there's a sudden drop.  The system became unstable, hence all of the terrible weather, but it did keep trying to correct itself.

Then, in 1550, the climate just slipped off the rails. Even if we had no other evidence at all, we could use this graph to pinpoint the Little Ice Age.

Yet the real terror lies in what happens at the end there.  Since the 19th century, CO2 levels have gone rapidly off the scale.

Image:  C02 levels on Earth between 1000 and 2000.
Image: C02 levels on Earth between 1000 and 2000.

By the 17th century, our planet was in the grip of a mini ice age, as temperatures plummeted and rivers froze. 

Liam further clarified this for us.  "The changing temperatures meant that the weather systems moved in different ways.  It's like what is happening today, when warm fronts and cold fronts meet in ways that they wouldn't usually.  Sandy was due to two smaller storms colliding, as weather fronts shifted, causing a monster storm instead.

"That's also what they experienced during the Little Ice Age."

So what happened next?   We patently came out of it!

Liam could read that story into the CO2 statistics too.  "From 1760, the CO2 levels rose; then plateaued by 1800.  This brought more settled weather and stabilized the weather systems."

As an historian, I could provide some further explanation here.  His Physics data had just deposited us into the Industrial Revolution.  Under the weight of heavy industry, humanity had begun burning a lot more fossil fuels.  It seemed like we'd saved ourselves!  Go us! 

Or had we?

"No."  Liam blithely informed me.  "The world began warming again before the Industrial Revolution.  The theories about that ending the Little Ice Age simply don't work when you look at the Physics.  But it did upset that recovery in the opposite direction.  It's sent us straight into another positive feedback loop, which is just now beginning to spiral out of control.  Expect more extremes of weather.  It's already begun."

What Caused the Little Ice Age?

There are so many theories about this, that I wanted to run them all past Liam. Some are modern and some are contemporary.

One thing which did puzzle me is why science hasn't yet come up with the definitive answer.  We have dozens of theories, but no climatologist stating, "It was this!  Let's not do that again!"

Liam blamed the data.  "Unless we discover more evidence, there is no definitive answer." 

The trouble is that the kind of statistics that we keep today weren't kept by Medieval meteorologists.  We can only extrapolate from what they did report, or from the evidence trapped in ice cores or tree rings.

Even those scientists steeped in this field, educated and highly informed guesses are all that they can provide.  So let's explore some of those theories.

There was less radiation from the sun during this period. It fell by half a percent.

"From 1645-1715, the Maunder Minimum fits perfectly with the dates of the worst years of the Little Ice Age.  Before that were the Wolf and Spörer Minimums.  It's all way too exact to be entirely coincidental."

But what does that all mean?

"Low solar activity means that there is less energy reaching the Earth from the sun.  Historically, low sun spot activity has led to colder temperatures on Earth."

However, Liam was also cautious about this data.  "The evidence is controversial; and we don't fully understand the connection between sun spots and temperature.  We just know that historically it has worked.

"Plus this doesn't make sense over a short period of time.  It can only be seen in a long cycle."

He further warned that the correlation is no longer working.  Further evidence that we're currently in a positive feedback loop, where all the rules no longer apply?  I never thought to ask him!

Five major volcanoes erupted during this period.

"This could be an important factor.  Volcanoes fill the atmosphere with sulphur, and sub-particles like ash and dust.  It blocks out the sun's radiation, leading to a cooler planet and creating weird effects in the atmosphere.

"When Yellowstone erupted, it nearly made us extinct."

It was God being angry at the population for various reasons.

There were a lot of these contemporary theories, with Catholics blaming Protestants; and Protestants blaming Catholics. Everyone blaming Witches and Jews.

Liam was quite blunt here. "According to science, none of these theories are valid."

The population of Europe had boomed during the Warm Period immediately before.

More people equated more deforestation, which meant that there were fewer trees to soak up carbon dioxide.

"Massive changes in population can alter weather.  There's a lot of evidence that Genghis Khan's wars did have an effect on the climate. 

"There are also two studies which argue that the collapse of the Native American population, after 1500, created wildernesses and forests, where there had once been arable land." 

Liam has provided links to those studies, so that we can read for ourselves.  However, he isn't convinced that this was a factor in causing the Little Ice Age.  He added, "The evidence is contradictory in this case."

I did point out that prior to the Little Ice Age, in the Medieval Warm Period, the population had grown faster than ever before.  But the 14th century had also devastated it.  Between famine, freezing temperatures, the Black Death and wars, the numbers of human beings on the planet had severely slumped again.

Liam saw nothing there to change his earlier opinion that the evidence is too contradictory to fully account for the Little Ice Age.

Evidence for the Postconquest Demographic Collapse of the Americas in Historical CO2 Levels
This article promotes the hypothesis that the massive demographic collapse of the native populations of the Americas triggered by the European colonization brought about the abandonment of large expanses of agricultural fields soon recovered by forests, which in due turn fixed atmospheric CO2 in significant quantities.

Ecological-Hydrological Effects of Reduced Biomass Burning in the Neotropics after A.D. 1500
Massive, pandemic-induced mortality in the Americas during European conquest yielded profound changes in human-landscape interaction identifiable in paleoecological and paleoclimatic records.

Witchcraft Trials in Post Medieval Europe

It's no coincidence that the Burning Times really kicked off from 1550. The Catholic Church had to explain the Little Ice Age somehow!

It was Witchcraft.

This was a contemporary theory. It resulted in the major witch-hunts, after Pope Innocent decreed that this was the reason behind the terrible weather.

"The Pope should apologize." 

Liam's response led to a vaguely tongue in cheek discussion of this one, as I'm a Wiccan.   Our joint conclusions were that this might have had an indirect effect on the conditions of the time.  After all, over 35,000 men, women and children burnt at the stake means over 35,000 less mouths to feed in a famine.

Plus there's all that wood being cut down for the fires, leading to further deforestation and increased levels of CO2 in the atmosphere. 

So, if this was to happen again, should people like me be subjected to religious genocide to correct it? 

"Witches didn't affect the weather."  Liam concluded, as a scientist always would.  "And the method of execution effects are too negligible to have factored into the climatic changes at the time."

That's a relief.

Also, as a Wiccan historian who wrote a dissertation on the subject, I can categorically state that there is nothing in our lore which suggests guilt.  Witches (and occultist Dion Fortune) did claim responsibility for the storm which blew the Spanish Armada off course in 1588.  But that's it.

It was the Oceanic Conveyor belt being infused with fresh water from melting glaciers in the Arctic.

This was the theory so beloved of the History Channel documentary on the Little Ice Age.  It's also what caused the ice age in the movie The Day After Tomorrow.  So did Liam think that there was any credence in this being the cause of it all?

"There's certainly a logical progression to get to this."  He told me.  "Fresh water from glaciers doesn't mix well with seawater.  They don't have the same flow; and there is a different density."

In short, letting the sea get too cold, in the North Atlantic, really could cause temperatures to drop everywhere else.

It was the devil.

This is another contemporary theory and resulted in French priests performing exorcisms on glaciers.  The ice apparently did slightly retreat, but then came back and engulfed several Alpine villages.

I put it to Liam that holy water may combat climate change to this level.  He didn't seem convinced.

"I can't imagine it would work."  He concluded.  Then added, "My knowledge of theology isn't very strong, but I thought that exorcisms could only be performed on living creatures.  People who have been possessed by demons.  Glaciers aren't living."

Time to bat that one back to the Catholic Church.  Any takers?

It just happened as part of a natural cycle and nothing in particular caused it.

"It is entirely possible, with regard again to a positive feedback loop.  But unlikely in this instance." Liam pondered it.  "There are so many things which could have contributed.  You have to account for Milanković Cycles, volcanic eruptions, as well as the after-effects of the Medieval Warm Period just before.  Massive changes can be wrought by deforestation.

"To say it's natural is to discount a lot of data."

He went on to describe two studies, which were independently published in 1999 and 2006. They both demonstrated that the inherent variability of the climate isn't enough to account for the Little Ice Age.

Liam provided links to both of them, so that you can read those findings for yourself.

Global Warming in the Context of the Little Ice Age (PDF)
Understanding the role of volcanic and solar variations in climate change is important not only for understanding the Little Ice Age but also for understanding and predicting the effects of anthropogenic changes in atmospheric composition in the twentieth century and beyond.

The Medieval Warm Period, the Little Ice Age and simulated climatic variability
The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for ‘present’ climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA).

It was the Jews.

This is a third contemporary theory and resulted in massacres and/or expulsions of Jewish people in several European countries.

"Antisemitism has been rife in many centuries, and it was particularly advantageous in the Middle Ages."  Liam seemed to remember who he was talking to.  "This isn't a Physics theory.  Ask an historian!"

As an historian, I can confirm that Jews got blamed for everything that couldn't be pinned on witches (and some other things besides).  It's difficult to work out how precisely they may have affected the climate though.

I think we can safely put this aside as prejudice and state that, from both a Physics and History perspective, there's absolutely no credence in the theory.  Though, for completion's sake, I suppose I ought to check in with a Jew.

"Sheri!  Did your lot go causing ice ages in the Medieval and Post-Medieval period?"

My fellow Wizzley author responded, "I have looked into the issue and I can honestly say that I do not know how my ancestors would have been able to play around with sunspots, ocean currents, volcanic activity or anything else that has been suggested as responsible for the climate changes at that time."

That's cleared that one up then.

How likely is it that the Little Ice Age could happen again?

I'd nearly run out of theories to run by my Physicist, so I turned to my final question.  It must be one in the minds of many people by now, particularly with all of this talk of modern climate change. 

Could the Little Ice Age happen again?   I was hoping for a resounding no.  I didn't get it.

"In the current climate, we don't know.  We're in untested waters."  Liam was referring to the fact that the meteorological records have never looked quite like they do in the 21st century.  "There is no evidence about what happens when we heat up in such a short period of time. Global temperatures are predicted to rise five degrees in the next 100 years.  We're just getting hotter and hotter.  

"Unless something big happens, not going to have anything like the Little Ice Age for a while. But we don't know.  As I said, we're in untested territory.  It's going to get hotter and wetter, stormy, and we're unlikely to get summers. India will bake. The Sahara will flood; or not.  We don't know."

There was one related theory, which I hadn't mooted yet.  I asked it now.  "What's your opinion on the fact that there is no such thing as global warming?   We are, in fact, still coming out of the Little Ice Age."

"They're wrong."  Liam pulled no punches.  "They are misunderstanding how climate works. Temperatures do go up and down, but the Little Ice Age was relatively rapid.  We've gone up way too rapidly for it to have been natural conditions."

And that's all!   Thank you very much to Liam Dodd for taking the time out of his studies to look at this fascinating moment in history. 

Books about the Little Ice Age and Climate Change

The Little Ice Age: How Climate Made History, 1300-1850

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The Climate Crisis: An Introductory Guide to Climate Change

An incredible wealth of scientific data on global warming has been collected in the last few decades. The history of the Earth's climate has been probed by drilling into polar i...

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Storms of My Grandchildren: The Truth About the Coming Climate Catastrophe and Our Last Chance to...

In his Q&A with Bill McKibben featured in the paperback edition of Storms of My Grandchildren, Dr. James Hansen, the world's leading climatologist, shows that exactly contrary t...

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The Hockey Stick and the Climate Wars: Dispatches from the Front Lines

The ongoing assault on climate science in the United States has never been more aggressive, more blatant, or more widely publicized than in the case of the Hockey Stick graph --...

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Climate Cover-Up: The Crusade to Deny Global Warming

Talk of global warming is nearly inescapable these days — but there are some who believe the concept of climate change is an elaborate hoax. Despite the input of the world’s lea...

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With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change

Nature is fragile, environmentalists often tell us. But the lesson of this book is that it is not so. The truth is far more worrying. Nature is strong and packs a serious counte...

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Updated: 02/05/2014, JoHarrington
Thank you! Would you like to post a comment now?


JoHarrington on 01/11/2013

Thank you very much. It was a true education talking to Liam. :)

TedWritesStuff on 01/10/2013

Great article! ;-)

JoHarrington on 12/21/2012

Ragtimelil - You got your question in just in time. I'd just arranged to speak with him about this. It was a good question too. I had to include that YouTube video. I know it's very simplistic, and aimed at children, but it really clarified the way the feedback loops worked. Poor Liam, he spent ages describing it to me too!

Sheri - Yep! You get to be our resident expert on all things Jewish. Good luck! And nope, it wasn't the Witches either. I should track down a Protestant and a Catholic to see if they did it,

Sheri_Oz on 12/21/2012

Well, now that I have been made expert on the subject of The Jews, I better make sure I really know what I'm talking about. Yup. It's true. This one can't be blamed on us!

Ragtimelil on 12/21/2012

Fascinating and scary (especially if you believe in reincarnation.) I liked the video on positive and negative feedback. That really made it clear to me.
And thanks Liam, headgear notwithstanding....

JoHarrington on 12/21/2012

Did you see that I added a quotation from Sheri Oz? You called it correctly. The Jews had nothing to do with it. :)

Thank you again for doing this. You always sound professional when you start talking about Physics!

Liam Dodd on 12/21/2012

This makes me sound so much more professional than the misfitting hoodies and beanie hats seem to imply.

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