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The Little Ice Age (LIA): Skeptics skating on thin ice

September 9, 2010

 Climate change skeptics suggest that because the climate has changed dramatically in the past – and without man’s intervention – it is possible that current changes to the Earth’s climate are also a natural event. You may be familiar with paintings depicting Londoners skating on the frozen River Thames, when winters, at least in the northern hemisphere, were more severe. The beginning and end of this period are subject to various interpretations, but the period is referred to as the Little Ice Age (LIA) and occurred between the 16th to 19th centuries.

Limited History

If we are to understand the LIA, we need to figure out what caused it. Scientists have examined several important strands of evidence about the LIA, including the activity of the sun, of volcanoes, and ocean heat circulation, principle drivers of natural climate change.

The activity of the sun can be assessed by looking at proxies – processes we know are affected by the sun’s activity. One of these is the formation of the radioactive isotope Carbon-14 in the atmosphere, which plants then absorb. By measuring carbon-14 in tree rings and other materials we know are from a certain period, we can estimate how active the sun was at the time. This graph shows the sun’s activity over the last millennium:

The carbon-14 data used in this graph go up to 1950. The graph below gives a fuller picture, showing that in the last three decades, the sun’s normal cycle of activity has remained steady, while temperatures have shot up:

Yet while the dips in solar activity correlate well with the LIA, there are other factors that, in combination, may have contributed to the climate change:

  • Volcanic activity was high during this period of history, and we know from modern studies of volcanism that eruptions can have strong cooling effects on the climate for several years after an eruption.
  • The ‘ocean conveyor belt’ –  thermohaline circulation – might have been slowed down by the introduction of large amounts of fresh water e.g. from the Greenland ice cap, the melting by the previous warm period (the Medieval Warm Period).
  • Sudden population decreased caused by the Black Death may have resulted in a decrease of agriculture and reforestation of agricultural land.

Can We Draw a Conclusion?

In truth, not really. The Little Ice Age remains for the present the subject of speculation. The most likely influence during this period is variable output from the sun combined with pronounced volcanic activity. We know that from the end of the LIA to the 1950s the sun’s output increased. But since WW2 the sun has slowly grown quieter, yet the temperature on Earth has gone up.

The skeptical argument that current warming is a continuation of the same warming that ended the LIA is unlikely. There is a lack of evidence for a suitable forcing (e.g. the sun) and numerous correlations with known natural forcings that can account for the LIA itself, and the subsequent climate recovery. Taken in isolation, the LIA might cast doubt on the theory of climate change. Considered alongside the empirical evidence, model predictions and a century of scientific research into the climate, recovery from the LIA is not a plausible theory to explain the observed evidence and rate of global climate change.

Footnote: this post was written for SkepticalScience as part of an ongoing project to add ‘basic’ rebuttals of common climate change denial arguments. References for all statements can be found in the intermediate discussion “We’re coming out of an ice age?”.

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21 Comments leave one →
  1. klem permalink
    September 9, 2010 8:31 pm

    Wow that’s a terrific article, I thought you were going to simply blame CO2 and of course human contribution of CO2. Instead you don’t even mention CO2. If co2 didn’t cause the LIA, nothing else really matters. The skeptics are still skating on thick ice.

    Skeptics don’t deny climate change, just anthropogenic climate change.

    Cheers!

  2. elsa nasser permalink
    September 9, 2010 10:20 pm

    “Can We Draw a Conclusion? In truth, not really. ”

    I never thought I would read you saying anything so sensible. Yes this is a terrific comment as Klem says. Why on earth you don’t apply the same logic to CO2 I don’t understand. You are 100% right here. We just don’t really know what drives temperature changes, whether in little ice ages or the current warmer period. We would do better to admit our ignorance rather than pretending that we have the knowledge.

  3. Simon permalink
    September 10, 2010 4:33 am

    There is not one reason for climate change because there is not one solitary human action that has been responsible. Instead there have been natural changes to the climate and 7 billion individual actions all contributing to CC. This Human component to the problem now requires 7 billion alternative actions that do not cause climate change. Although initially we have to find the natural balance points that ensure stable climatic conditions.

    It is not going to be enough to just cut co2. We may also have to reforest our farmland for the natural balance to be restored
    Currently 4 billion people rely on consumerism for everything including life itself. Cutting waste and consuming less energy is not an option as this negatively affects economic growth. Waste and greed is good economically and bad in every other sense, these two concerns represent diametrically opposed goals and objectives while the powers that be fight for our rights to be wealthy and free to choose our own destiny.

    Providing that we have the money from consumerism we have the freedom to choose without it there will be no democracies just little communities of self sufficient collectives trying to survive in a decentralized world.

    Not a bad future and one that can be achieved with the outbreak of something like the black death.

    Would the black death be enough today?

  4. Graham Wayne permalink*
    September 10, 2010 6:22 am

    “Cutting waste and consuming less energy is not an option as this negatively affects economic growth. Waste and greed is good economically”

    Hi Simon. Thanks for the comment but I can’t agree with these statements at all. Cutting waste and using less energy are only ruled out by those who think there is no alternative to endless economic growth. Google Hermann Daly and read about steady state economics for a rather more progressive take on the subject. Wealth creation may not be the issue, which may be more about wealth distribution and what we use as the measure of our own happiness, for while we think we can only be more happy by owning more ‘things’, the consumerist desire for growth will remain the driving force behind global economics, and climate change will not be adequately addressed.

    As for waste and greed being good economically, I must tell you that is simply wrong. In commerce – where I spend most of my professional life – both are considered bad for business. Waste is simply the loss of profit that could otherwise be added to the balance sheet (it’s culpably stupid in commercial terms) and greed is that which drives short-termism, fraud, deceit and workforce abuses such as disregard for health and safely. Neither are desirable, nor good business practice. By extension, I would say the same is true for the public and their domestic economics.

  5. Graham Wayne permalink*
    September 10, 2010 6:31 am

    Elsa says: “Why on earth you don’t apply the same logic to CO2 I don’t understand”. I know you don’t want to understand, Elsa. The reason, however, is that the logic that applies to a historical event for which we have very little data at all cannot also be applied to the present day with its satellites, computers, DNA, nuclear power and all the other demonstrations of gains made in understanding the universe we live in. In light of this massive increase in our knowledge, it is ludicrous to say “We just don’t really know what drives temperature changes, whether in little ice ages or the current warmer period”. It just isn’t true – but it would suit your agenda to make such a spurious claim, would it not?

    Every day that passes brings us a little more knowledge, a better and sharper tool, a clearer and more precise way of analysing the prodigious data we now routinely collect. Pretending otherwise simply reveals the problem with your position: you can’t find any science to support it, so you deny the science exists. Guess what name we give to people who deny the science?

  6. elsa permalink
    September 10, 2010 4:29 pm

    Every day may bring us greater information about temperature changes. But it does not add to our knowledge of the relationship between CO2 and temperature. Quite rightly you see through the lack of any proper established relationship between the sun’s activity and temperature as outlined above, but your own CO2 relationship theory is no better. You should apply the same scientific rigour to your own pet theory. How on earth could you isolate the effects of CO2 from all of the other factors that may alter the temperature? And if you are so sure that there is a relationship tell us what it is. As I asked elsewhere on your site: if T is the mean temperature of the earth and C is the concentration in parts per million of CO2 in the atmosphere how should we express T in terms of C?

  7. elsa permalink
    September 10, 2010 4:39 pm

    Oh dear Simon, what a terrible outlook and a load of nonsense. As Graham very rightly points out the idea that waste is considered good by anyone is just not true. No doubt greed is admired by one or two but not many that I have come across. I am looking forward to the days when most Chinese and Indians can enjoy the sort of life that I do and probably as you do too. Of course when they do the world’s economy will be much larger and that is to be welcomed not sulked about.

  8. Graham Wayne permalink*
    September 10, 2010 4:43 pm

    Esla, I swear you haven’t understood anything I’ve written.

    “…you see through the lack of any proper established relationship between the sun’s activity and temperature…”

    This is completely incorrect. I have documented the lack of historic data about the relationship between the sun’s activity and temperature, not the lack of a relationship. The relationship is, in fact, utterly straightforward – the higher the TSI, the greater the temperature. The sun gets hotter, so do we. It doesn’t get any more straightforward than that!

    What ‘pet theory’? Are you referring to the theory of anthropogenic climate change?

    ” if T is the mean temperature of the earth and C is the concentration in parts per million of CO2 in the atmosphere how should we express T in terms of C?”

    You can’t. The question is entirely inappropriate. The relationship is indirect: the temperature increase caused by GHGs, which is 30 degrees C in total, of which the CO2 contribution is about 17%. You cannot directly associate T with C because C delays re-radiation through downward scattering, not by creating heat – heat is a function of the amount of long wave radiation reaching the earth. The real relationship between T and C is, if you like, that T is wrapped in a blanket of C, because CO2 affects the time it takes for heat to leave the earth to go back into space.

  9. elsa permalink
    September 10, 2010 5:43 pm

    I think you do me a bit of an injustice. You do need to keep the “as outlined above” bit when quoting from me. I don’t doubt that there is a relationship between solar activity and temperature but as you make clear the historical data, such as it is, is not very demonstrative of the relationship. I don’t doubt either that there is some relationship between CO2 and temperature but it is just as dodgy. So dodgy that you seem unable to answer a very reasonable question, namely what is the equation that links the two? If you say you cannot directly associate T with C then how do you manage to attribute such temperature increase as there has been since 1975-1980 to CO2?

  10. adelady permalink
    September 11, 2010 2:29 am

    I’m not sure what you’re getting at Elsa. Are you saying that CO2 can have no relationship with temperature in the atmosphere? Or that additional CO2 can have no effect on increasing temperature above its previous or normal blanketing effect without the addition from burning fossil (carbon sink) fuels?

    The basic physics of gases gives us both CO2 lasers and the atmospheric effect of CO2 concentrations, among other things . That also gives us the basis for the calculations of how increases and decreases in CO2 can affect the temperature. As I read it, the complications in temperature calculations arise from balancing all the possible influences on temperature, sun, albedo, oceans, etc., not from anything about CO2 itself.

  11. Graham Wayne permalink*
    September 11, 2010 6:21 am

    Adelady – you make a good point. This relationship business is ill-defined in the context of climate. If we discuss the relationship between CO2 and heat (instead of temperature) then the relationship is exactly what Tyndall discovered, and is governed by the absorbtion bands of CO2 and the kinetic energy per mole that can be stored prior to re-radiation.

  12. elsa permalink
    September 11, 2010 11:36 am

    Adelady and Graham, forgive me but do you not think that a bit odd that on the one hand you feel able to say that the warming of the earth by a fraction of a degree is due to the increase in CO2 concentration and that if the concentration of CO2 continues to increase then the temperature will increase by so much that terrible consequences will follow but on the other you cannot apparently even begin to set out the relationship between CO2 concentration and temperature? If as you say Graham the relationship is ill defined (which if I may say so is exactly what I have always said to you but you have denied) on what basis do you claim the knowledge that the earth will warm by x degrees if CO2 concentration e.g. doubles?

  13. adelady permalink
    September 12, 2010 7:52 am

    Elsa, I don’t know about Graham but I’m not a scientist, but I have little trouble following the arguments of expert scientists. (Until I come across equations that look like trouble – meaning too much time, effort and trouble to check myself.) But I have no problem in relying on people who have done the work and do know what they’re talking about.

    I’ve not devoted endless hours to perusing the IPCC reports, mainly because that would entail even further hours following the cites. I follow cites only when the discussion is in an area that interests me at the time like ocean acidification or the current Arctic melt.

    If you say you can’t rely on 150 years’ worth of work on the physics of gases, you (or anyone else who says the same) are between a rock and a hard place. Unless you’ve got the time and energy to get a PhD in physics, you really do have to rely on the best efforts of the people that do have those qualifications and have done the work since.

    The other thing you have to bear in mind is, if someone did say OK it’s not CO2. What then? Two things follow. One, we have to explain the rise in temperatures having a cause other than CO2 – having already eliminated the sun and half a dozen other candidates. Two, we need a wholesale discarding and replacing of the physics describing the properties of CO2. (What would we then do about all the CO2 lasers around the world?)

    The atmosphere equation for CO2 alone? 1 degree C rise for every doubling of CO2 concentration in the atmosphere. (Given the current earth orbit.)

    The atmosphere temperature result following from that? Balancing the feedbacks and all the other forcings, generally covered by the term sensitivity, anywhere from 1.5 to 6 degrees C. Currently estimates range through 2 or 3 degrees.

    The uncertainty? No-one can absolutely rule out 6 degrees. That’s the terrifying one. Generally people think that further work will narrow the uncertainties and hope that the narrowing leads to a result in the middle or lower part of the range – but we have no guarantees of that.

    The other uncertainty. Just how dependent are the current theories on the temperature profiles we’re accustomed to? We’re quite content with an earth where the temperature over the Antarctic is below -40 degrees C and the tropics are at 35+ degrees C for months at a time – all resulting in a global average above 15C. How much will both the local and global temperatures change when we reset at a higher baseline?

  14. elsa permalink
    September 13, 2010 9:25 am

    Adelady, I think you are jumping too far ahead. In order to be able to arrive at the likely change in temperature from a change in CO2 concentration (which you do give, although in a form that we cannot test in advance) you need to know what the relationship is between the level of the temperature and the concentration of CO2. This is not a relationship that is given by “scientists” perhaps because it would be very easy to test and it would soon become apparent that the relationship does not match the facts at all well. While I completely sympathise with your view on the IPCC reports etc I do not see that there is 150 years of physics behind the whole warmist approach. There is a limited amount of physics behind it but it does not add much to the debate and, as far as I know, it does not give us the equation that I am asking for, which must be central to the whole debate.

  15. Graham Wayne permalink*
    September 13, 2010 9:46 am

    Elsa:

    “you need to know what the relationship is between the level of the temperature and the concentration of CO2”.

    We do know, Elsa. It is defined by the percentage of GHGs in the atmosphere and the temperature increase they induce – around 30 degrees C. As I already said, CO2 contributes around 17% of this (that’s the middle estimate out of the range). So of that 30 degrees, a little under one sixth is the CO2 contribution i.e. 5.1 degrees.

    “This is not a relationship that is given by “scientists””

    Given the nature of your questions, it seems you want to dispute Arrhenius, who did the first measurements of the greenhouse effect. And don’t put ‘scientists’ in quotes because you don’t like what they say. This kind of humbug just pisses me off. These are very highly qualified people, some of the best scientists in the world, and you attacking them is unworthy and disasteful. I could ask what kind of ‘statistician’ you are – would that help you understand my point? Attacking someone’s qualifications – even by insinuation – simply demonstrates the paucity of one’s own arguments.

    Other than that, as Adelady points out, you are talking about climate sensitivity – 1 degree rise for a doubling of CO2 without feedbacks . Now please see my remarks about moderation and climate change denial. If you have issues, you must find somewhere else to express them, and I suggest Skeptical Science, where this article first appeared, and where the arguments offered by skeptics are valid subject of discussion.

  16. adelady permalink
    September 13, 2010 1:38 pm

    I must be psychic! I saw this (quoted below) in a comment at Skeptical Science and instantly thought of this thread. It’s a lot better than what I wrote earlier about CO2 and balancing forcings and feedbacks. I’ve changed only the paragraphing to emphasise the point.

    ” Extensive research has narrowed current ‘climate sensitivity’ to a range between roughly doubling warming from a forcing (in this case human CO2 emissions) to multiplying it by as much as a factor of five (with higher values considered very unlikely, but not completely ruled out). To ‘disprove’ that with a lower climate sensitivity you’d have to show some climate process which all that prior research overlooked or miscalculated.

    In the mean time, ponder this… climate science says a doubling of CO2 from the historical ~280 ppm to 560 ppm would produce about 1 C of warming and that feedbacks would increase this to at least 2 C or more (best estimate is currently about 3 C).

    We are presently at about 390 ppm… a 40% increase. Yet we have already seen over 0.8 C of warming.

    We’re at nearly 1 C warming with less than half the CO2 increase needed (by itself) to get us to that point. How does that NOT indicate that net feedbacks are positive and significant? Especially since it is right in line with the projections of 3 C for doubling of CO2? “

  17. Graham Wayne permalink*
    September 13, 2010 2:17 pm

    Adelady – that’s a good point. I like that as much as JC’s point about that the MWP could only have occurred if the climate sensitivity was high.

    I’m not surprised that things are worse than we think. I’m reading a paper at the moment that suggests the reporting bias in the media actually suppresses the bad information, and that most of what’s going on right now is considerably worse, and more advanced, than is being reported. I’ll be writing this up shortly, but if you’re interested Google “asymmetry of
    scientific challenge” and it’s lead researcher, William R. Freudenburg. There’s a nice ABC transcript of him, Naomi Oreskes and others talking about this here:
    http://www.abc.net.au/rn/scienceshow/stories/2010/2859986.htm

  18. elsa permalink
    September 13, 2010 10:22 pm

    Adelady and Graham,
    All I asked you to do was to give the equation. Not what would happen if the concentration altered by 40% or 100% or any other number. Something much simpler than that. If T is the mean temperature of the world and C is the concentration in parts per million, express T in terms of C.
    Not an unreasonable request surely?

  19. elsa permalink
    September 13, 2010 10:24 pm

    PS and sorry that it has all come to moderation. It is very good of you to have hosted this site.

  20. adelady permalink
    September 14, 2010 6:37 am

    Thx, Graham. They were worth the time.

  21. Graham Wayne permalink*
    September 14, 2010 6:58 am

    Elsa “Not an unreasonable request surely?”

    Actually, it isn’t that it’s unreasonable, it’s that the question is unscientific. There is no direct relationship between CO2 PPM and the earth’s temperature. CO2 and other greenhouse gases affect the rate that heat re-radiates back into space. The correct question – assuming you seek an answer – is to express the effect of GHGs on the theoretical black body equation – maths that is widely published so I won’t repeat it here (not to mention I barely understand it, so I’d probably make an ass of myself discussing it).

    Let me give you an example of the way you’ve formed a question that can’t really be answered. The sun’s output affects the growth of plants – like wheat. When the sun’s output is low, wheat grows less (say) so the market price goes up due to shortages. You are asking, by analogy, for a mathematical expression that defines the relationship between the sun’s output and the price of wheat.

    But look, none of this relates to the LIA, the subject of this post. Don’t you see that my moderation problem comes from arguments like this, which have nothing to do with the LIA and everything to do with your scepticism. This isn’t the place to air your views Elsa, just because it happens to be – in the broader sense – about climate change. If you keep posting these questions I’m going to have to disallow them and I really don’t want to do that, because actually you’re rather a nice person. If you have anything to say about the actual topic your remarks are welcome. General scepticism about climate change must be voiced elsewhere.

    Please respect my views on this Elsa – I don’t want to be forced to play the bad guy. And if you think I’m ducking the question, why don’t you post it in a place where a lot of (very polite) scientists hang out – the thread under the original Skeptical Science post of mine on this topic. See what they say – they know a lot more about this than I do.

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