The Little Ice Age was anthropogenic?

Climate change denialists love to bring up the Little Ice Age (and the Medieval Warm Period before it) as examples of natural variation in climate that wasn’t human-caused, and therefore cast doubt on all the arguments about anthropogenic climate change. Except…what if the cooling recorded for the 17th-19th centuries was actually caused by human activity? A new analysis suggests that that might be our fault, too.

It’s the UCL group’s estimate that 60 million people were living across the Americas at the end of the 15th Century (about 10% of the world’s total population), and that this was reduced to just five or six million within a hundred years.

The scientists calculated how much land previously cultivated by indigenous civilisations would have fallen into disuse, and what the impact would be if this ground was then repossessed by forest and savannah.

The area is in the order of 56 million hectares, close in size to a modern country like France.

This scale of regrowth is figured to have drawn down sufficient CO₂ that the concentration of the gas in the atmosphere eventually fell by 7-10ppm (that is 7-10 molecules of CO₂ in every one million molecules in the air).

“To put that in the modern context – we basically burn (fossil fuels) and produce about 3ppm per year. So, we’re talking a large amount of carbon that’s being sucked out of the atmosphere,” explained co-author Prof Mark Maslin.

It’s horrifying enough that the American genocide killed about 50 million people, but that it was so immense that it affected the climate is stunning. I also have to wonder how much the earlier Black Death in Europe contributed to a decline in CO2.

This does suggest an obvious solution to our current climate change concerns. Annihilate a few billion people, and the problem goes away.

It looks like the American and Russian leaders are working on a plan to do just that.


  1. Oggie. My Favourite Colour is MediOchre says

    I also have to wonder how much the earlier Black Death in Europe contributed to a decline in CO2.

    Quite possibly.

    Vast areas of central and western Europe were passively reforested beginning in the early 1500s. Between the 100 years war (among many wars (sorry that I cannot remember anything but the Valtelline war in Italy (and I’m not even confident I have that in the right century))which did a very good job of removing many small villages and towns from existence and the advent of bubonic and pneumonic plague, populations in what is today France, England, Germany, Austria, Switzerland and Italy plummeted. Fields returned to pasture, pasture returned to scrubland, scrubland returned to forest. Since even a small tree (like a silver maple) can sequester 200kg of carbon, this could remove a great deal of carbon from the atmosphere. The Domesday Book of England records hundreds of villages that had disappeared by the early modern era, replace by forests. On the flip side, though, in Germany, forest growth (and regrowth) was severely limited during the Little Ice Age by unfavourable growing conditions leading to fuel shortages by the 17th century.

    This is possible, though. A great deal of evidence has been found supporting the role of botanical carbon sequestration in the Carboniferous and Permian bi-polar ice ages. About 90% of the worlds coal was formed in equatorial rain forests during this fairly short (geologically speaking) period of time which saw repeated pulses of extremely high atmospheric oxygen combined with extremely low atmospheric carbon. So forest growth can affect both carbon and oxygen levels enough to still be noticed 300 million years later.

    Whether reforestation in North America and Europe could sequester that much carbon? My gut feeling is no, but gut feeling are notoriously wrong.

  2. Mark Dowd says

    Even their stupidly irrelevant arguments (just because it was natural before doesn’t mean it’s natural now) end up being wrong. They grasp at straws, but even the straws turn out to be fake.

  3. davidnangle says

    I imagine the “kill most of humanity and steal all the free property after” plan was stumbled upon accidentally in the first place, but then widely accepted as a good plan forward by the 0.1% some time ago.

    The sad thing about this is, it will probably work really well. And the survivors will be the people murdered billions. The Earth will belong to genocidal sociopaths.

    Silver lining: most of the people tricked into defending the 0.1% while they murder us will, of course, be murdered as well.

  4. Oggie. My Favourite Colour is MediOchre says

    This does suggest an obvious solution to our current climate change concerns. Annihilate a few billion people, and the problem goes away.

    It looks like the American and Russian leaders are working on a plan to do just that.

    I remember back in the 1990s, when the idea of global warming was first percolating into general popular relevance (as opposed to scientific relevance) worrying that conservatives would see nuclear winter as an antidote to global warming. I didn’t even think of the added bonus of population reduction.

  5. Reginald Selkirk says

    … close in size to a modern country like France.

    Curious phrasing. What does modernity have to do with size? Possibly they meant something like “close in size to modern-day France“. Was this translated from a foreign language? BBC, UCL – perhaps from British English?

  6. slithey tove (twas brillig (stevem)) says

    I’m confused, it looks to me like the paper is saying CO2 was taken outt of the atmosphere by the regrowth of the forests. I don’t understand how that can produce the same effect as our dumping CO2 into the atmosphere.
    Not asking to explain my mistake, would really appreciate someone pointing out how I’m misreading.
    — Need more coffee to get my brain fired up. Thank you

  7. Akira MacKenzie says

    slithy tove @ 5

    The regrowth of forests after drastic population decline took CO2 out of the atmosphere resulting in global cooling, not warming.

  8. numerobis says

    This isn’t a new argument; what’s new is the greater specificity in the measurements.

    The argument as I heard it was that, contemporaneous with that, there was also upheaval in China that would involved a similar number of deaths.

    There’s also some evidence of warming due to deforestation caused by the spread of agriculture in the bronze age (along with a large increase in sediment flow).

    Those are two of the markers of the anthropocene that have been proposed to spot the age prior to the 20th century deposits from nuclear weapons testing and leaded gasoline.

  9. Bruce says

    While ending peacenik Reagan’s Intermediate IMF treaty might lead to an intermediate nuclear was and intermediate nuclear winter fallout, it might not be so simple. Even if the population were reduced by 90% again, that might not affect land under clearance. That’s because most US farmland is now corporate owned. While people are mortal, corporations are immortal, my friend. So corporations would keep hiring people to keep their farmland all plowed forever. That is, as long as the economic supply chain provides fuel for farm vehicles. The only way Trump can cut farming is by an intermediate nuclear war causing enough destruction to cause a big recession that destroys the economic demand to buy corporate supplied food. That is, Trump will kill enough Americans that we dead people will boycott corporate farms. That will show us!

  10. wanderingelf says

    This idea is part of the early anthropocene hypothesis proposed by Bill Ruddiman around 15 years ago.
    I had a chance to meet Ruddiman and talk to him about it briefly circa 2005 when he gave an informal presentation on his hypothesis to a group of us paleoclimate geeks at the UMN. Since then, there has been debate over just how big those preindustrial anthropogenic impacts on greenhouse gases were, and whether they were big enough to have the effects claimed by Ruddiman. This appears to be one of the latest developments in that debate.

  11. lumipuna says

    I suppose this wouldn’t be an anthropogenic cooling effect, but rather a temporary lapse in the anthropogenic warming effect that goes back to the neolithic?

    As for Black Death, I understand it caused only a temporary dent in Europe’s population that was generally growing through the late middle and early modern ages. Instead, I’ve seen emerging estimates that population and agriculture in tropical Africa also declined around 17th century, the peak of Atlantic slave trade, roughly coinciding with America’s depopulation and the peak of Little Ice Age.

    (Export of slaves alone wouldn’t have made much dent in Africa’s population growth, but constant slave raids between nearby communities made farming difficult over many generations.)

  12. Jazzlet says

    Reginald Selkirk @ 5,
    France has varied in size over the centuries, as the previous two paragraphs are about four hundred years in the past the writers are being careful to be clear, that is all.

  13. monad says

    @9 Bruce: Corporations do not have any independent existence, though, they are legal constructs. They are maintained by multitudes of people who write and enforce the appropriate legal and economic frameworks. Hard to imagine why they would survive unchanged through a catastrophe that would wipe out most of those people and documents!

    A handful of survivors looking to rebuild their lives are not likely to be so dedicated to preserving the exact property arrangements from before. It reminds me of the rich who build shelters to ride out an apocalypse, complete with servants and guards who are just assumed should keep working for them after. As if their hoarded money would retain its value without the society that created it.

  14. madtom1999 says

    The wiping out of 90% of the native American population with disease was not genocide as it was not deliberate. Later attempts were genocide but this wasn’t.

  15. says

    Cross posted from the Political Madness All the Time thread, and related to the last link in PZ’s post.

    Trump is walking away from another treaty:

    President Donald Trump on Friday said the U.S. is suspending its involvement in the Intermediate-Range Nuclear Forces Treaty and would start the process of withdrawing entirely in six months.

    “For far too long, Russia has violated the Intermediate-Range Nuclear Forces (INF) Treaty with impunity, covertly developing and fielding a prohibited missile system that poses a direct threat to our allies and troops abroad,” Trump said in a statement.

    NBC News link

    From John McLaughlin, former deputy director of the CIA:

    The Trump administration’s plan to withdraw from the Intermediate-Range Nuclear Forces Treaty (INF) is the wrong way to respond to a real problem. If carried out, it would be dangerous, destabilizing and potentially counterproductive. […]

    First, when it comes to nuclear weapons, just giving up and walking away from an arms-control treaty reverses the wise course of negotiated reductions we have followed for decades. The likely consequence of killing this treaty is that Russia will build more nukes and so will we. There are about 15,000 nuclear weapons in the world and tons of explosive nuclear material; no one needs more. While nuclear weapons can be stabilizing, that effect is most apparent when there is a degree of cross-national transparency codified in arms control agreements. […]

    Second, this is wrong example to set for aspiring nuclear states such as North Korea and Iran. If the big guys can’t restrain the nuclear impulse, why should they? This is the absolute wrong moment to telegraph that to the Iranians, with President Trump having already jettisoned the U.S. nuclear agreement with them – and to Pyongyang, which has yet to follow through on its denuclearization pledges.

    Third, there’s a better way out of the INF Treaty dilemma. Why not try to turn it into an opportunity, as former U.S. senator Sam Nunn has suggested? Use the six-month withdrawal notice the treaty provides to follow through on the “Strategic Stability” talks that Trump and Russian President Vladimir Putin promised at their summit. In those, look for ways to resolve differences on this through inspections, information exchange and other measures of transparency. If that is impossible, at least try to renew momentum on arms reductions more broadly, recalling that our major nuclear agreement with Russia, New START, is set to expire in 16 months.

    Washington Post link

    From Steve Benen:

    […] Heather Hurlburt had a related piece, explaining how scrapping the treaty would further advance Vladimir Putin’s plans. Fred Kaplan made a similar argument.

    The point isn’t that Russia’s defiance should be tolerated. No one has made the case that the United States just look the other way in response to Putin’s actions in this area. The Trump administration has raised legitimate concerns, which are effectively identical to complaints raised by the Obama administration.

    Rather, the point is, simply walking away from the treaty and hoping for the best isn’t a real policy. There are alternatives that the White House can and should pursue.

    Trump has spoken on several occasions about a prospective “arms race.” I’m not sure he knows what the phrase means, but he’d likely figure it out if/when the INF Treaty ends.

    Postscript: When John Bolton took over as the White House national security advisor, and many expressed alarm at the kind of influence he’d have, today’s news is emblematic of those fears. Bolton has long opposed this and other nuclear treaties with Russia, and it’s likely he’d been pushing Trump to agree with this vision.

  16. a_ray_in_dilbert_space says

    Hmm. Even if the paper is correct, I see several issues:
    1) There is no convincing evidence that the Little Ice Age was in fact global rather than mainly a North Atlantic (N. America and Europe, mainly) phenomenon
    2) Forcing due to CO2 is logarithmic in CO2 concentration–so reducing the per-industrial atmospheric concentration from ~270 to ~260 affects CO2 forcing by less than 5%
    3) Reforestation would also reduce albedo, which would actually raise the shortwave energy absorbed.

    As pointed out above, the Anthropocene is a lot older than most people think.

  17. slithey tove (twas brillig (stevem)) says

    re Akira @7:
    aha! that’s what I was missing, the most obvious piece of the puxzzle: The title of the OP, Little ICE Age... I really did need more coffee then. dear me…

  18. davidnangle says

    David Klopotoski: Thanos only wanted 50%. The Kochs would want 95% dead, and most of the survivors living as slaves.

  19. brett says

    I also have to wonder how much the earlier Black Death in Europe contributed to a decline in CO2.

    It might have, although it’s hard to tell it apart from the weather just generally getting colder and wetter at the beginning of the 14th century.

    It could have been even worse. The Eurasian folk got extraordinarily lucky in that there wasn’t some Smallpox-esque level disease circulating around in the Americas that could have made its way to China and Europe along the trade.

  20. KG says

    The Eurasian folk got extraordinarily lucky in that there wasn’t some Smallpox-esque level disease circulating around in the Americas that could have made its way to China and Europe along the trade. – brett@21

    Well there was, according to most relevant experts, syphilis; which according to some, killed non-Americans far quicker then than it does now, even if untreated. But there are reasons to expect fewer infectious diseases in the pre-Columbian Americas: the founding populations were relatively small groups of foragers, and although many later farmed and population greatly increased, they domesticated relatively few animals. Epidemic diseases require large populations to maintain themselves, and most are derived from domestic animals.

  21. says

    You don’t need the genocide though. The effect is achieved by massive reforestation, which is entirely possible while maintaining the current population. The US for example gives over vast tracts of land to essentially pointless agriculture for mostly political reasons. You could feed the entire population of the earth from a fraction of the land currently used, even without moving towards new technologies. Reforesting a significant portion the globe would sequester a vast amount of carbon, though it’s unlikely to reverse the effects of industrial CO2 production.

  22. manytimesover says

    Anyone interested in the 10000 year anthropocene argument would do well to watch this nifty explanation.

    Basically, this geologist/astronomer explains CO2 release and absorption based on orbits and the counter-cyclical effects of agriculture at various times. One substantial hit to begin with – general agriculture – wasn’t enough to completely override the cyclical move to lower temperatures after a few thousand years. Then! Rice paddies! Methane, CO2 galore. And we’re off to the races all the way to the beginning of the industrial revolution.

    Anyone wanting something encouraging to urge them on can look to China for one huge regeneration exercise. The Loess Plateau There have been many others since.

  23. Pierce R. Butler says

    numerobis @ # 8: This isn’t a new argument; what’s new is the greater specificity in the measurements. &
    wanderingelf @ # 10: This idea is part of the early anthropocene hypothesis proposed by Bill Ruddiman around 15 years ago.

    Ftr, I read this hypothesis in Brian Fagan’s The Little Ice Age: How Climate Made History 1300-1850, published in 2001. Fagan also emphasized the paucity of data from everywhere except northern Europe.