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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Greenhouse gasses, principally CO2, have controlled most ancient climate changes. This time around humans are the cause, mainly by our CO2 emissions.

Climate Myth...

Climate's changed before

Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)

Greenhouse gasses – mainly CO2, but also methane – were involved in most of the climate changes in Earth’s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer. When CO2 levels jumped rapidly, the global warming that resulted was highly disruptive and sometimes caused mass extinctions. Humans today are emitting prodigious quantities of CO2, at a rate faster than even the most destructive climate changes in earth's past.

Abrupt vs slow change.

Life flourished in the Eocene, the Cretaceous and other times of high COin the atmosphere because the greenhouse gasses were in balance with the carbon in the oceans and the weathering of rocks. Life, ocean chemistry, and atmospheric gasses had millions of years to adjust to those levels.

Lush Eocene Arctic 50 million years ago

Lush life in the Arctic during the Eocene, 50 million years ago (original art - Stephen C. Quinn, The American Museum of Natural History, N.Y.C)


But there have been several times in Earth’s past when Earth's temperature jumped abruptly, in much the same way as they are doing today. Those times were caused by large and rapid greenhouse gas emissions, just like humans are causing today.

Those abrupt global warming events were almost always highly destructive for life, causing mass extinctions such as at the end of the PermianTriassic, or even mid-Cambrian periods. The symptoms from those events (a big, rapid jump in global temperatures, rising sea levels, and ocean acidification) are all happening today with human-caused climate change.

So yes, the climate has changed before humans, and in most cases scientists know why. In all cases we see the same association between CO2 levels and global temperatures. And past examples of rapid carbon emissions (just like today) were generally highly destructive to life on Earth.

Basic rebuttal written by howardlee


Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 6 August 2015 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Past

Please check the related blog post for background information about this graphics resource.

Further reading

RealClimate article published by Prof. Stefan Rahmstorf on July 20, 2017:

The climate has always changed. What do you conclude?

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Comments 326 to 350 out of 883:

  1. JasonB @ 324, Thanks for the link to Richard Alley's talk. He has a great way of making a 45 minute lecture seem to short. What a great teacher.
  2. Composer99: You are right, initially I took the large gap before the last two paragraphs as a "quote delimiter" but afterwards it occurred to me that it might still be part of the quote and checking the page at the URL given confirms this. Sorry Bill. Looking at what was written on that page, someone has clearly gone to a lot of effort to put together an argument that a little more effort on research would have told them was attacking a strawman. Even a cursory examination of the IPCC reports shows that mainstream science is well aware that "other factors besides atmospheric carbon influence earth temperatures and global warming" because it even quantifies those other factors in the attribution analysis! That mistake then leads to the erroneous conclusion that all that's required to disprove AGW is to show that other factors must have also influenced climate in the past. The underlying logic is the same as "Lightning has caused fires long before man came along, therefore arson doesn't exist". Or, "murder doesn't exist because people have died of natural causes in the past", used by the defence in a murder trial where the accused was seen by 97 witnesses standing over the body of the victim with a bloody knife in his hand shouting "I'm glad I killed the bastard!". (Apologies to BlackAdder...) (Three other witnesses aren't sure what they saw and even disagree with each other on what happened, but all agree it couldn't have been murder because that would require the state to raise taxes to employ a police force and one objects strenuously to the 97 others being so certain of what they witnessed.) Doug H: If you liked the talk, be sure to check out Ring of Fire. :-) It's hard to reconcile the reality of a funny, geeky climate scientist with the portrayal of them by commentors on sites like WUWT and Climate, Etc.
  3. JasonB @ 327, That is an extraordinary piece of teaching. A 3 minute video I will remember for a long time. I've even emailed the link to my family, so they can all enjoy it. If only science had been this much fun at school, my career path would have been very different. Thanks for posting it.
  4. JasonB:
    Three other witnesses aren't sure what they saw and even disagree with each other on what happened, but all agree it couldn't have been murder because that would require the state to raise taxes to employ a police force and one objects strenuously to the 97 others being so certain of what they witnessed.
    Touché.
  5. Doug H, Completely off-topic for this post, but related to the subject of Richard Alley's video: I recently came across research that showed that some subducting plates may make it all the way down to the bottom of the mantle, literally scraping along and piling up on the core, thousands of km down, because rock is such a poor conductor of heat that they take a really long time to melt. I found this image of plates plunging deep within the earth to be quite fascinating, although I can't remember where I read it now. I just did a quick search and turned up this paper: http://www.es.ucsc.edu/~ahutko/Publications/HLGR_Nature_2006.pdf Look at figure 4 in particular. As Richard Alley's song indicates, and this page confirms, the volcanoes above subduction zones are not actually emitting the melted plate (as I had assumed) but rather magma that has melted due to the water being carried down by the melting plate.
  6. JasonB @ 330, I have followed both your links with great interest. I am not a scientist, but my reading comprehension may be just about up to the task of understanding the pdf, if I filter it through enough red wine. The subd_zone.htm page is fascinating and, boy, has it expanded my vocabulary! Ultramafic, diapirs, amphiboles: I'm just dying to casually drop a few of those into a conversation some time. "8-)
  7. wow, I trawled through a lot of this some fascinating battles going on, and none dispassionate. On the one hand it seems scientists are fitting hypotheses around one data set (CO2) when the earth could be observed as a much more intricate system with too many observable forces than one.It depends how you look at it I suppose. It's like they're trying to find a theory of everything. I do reckon the industrial system produces too much stuff causing pollution in the atmosphere like satellites, what's the carbon footprint on a couple of satellites? I think if we all just slowed down a bit, stopped our industrial systems and stopped funding university's and science programs, life would be less splintered and more holistic and we could observe the natural rythyms of life and ourselves. also its very fatalistic, you can make all this effort and then a solar comet is just round the corner at any given moment/ like in the plastacene era. Whats the point of all the scaremongering. Think of the children guys.
  8. Dan, you're right: if we de-funded the education system, life would be simpler. We'd all believe whatever our priests told us, we'd have much shorter lifespans, and most of us would be in the ag industry (and not as property owners). We would not be swilling down Nut Browne Ale in a Public House in Merry Olde Englande. Actually, we'd probably all be dead. If AIDS had developed in 1400 instead of the 1970s, it would have been much worse. And children? What was the global child mortality rate in 1700? What's the point of all the scare-mongering? Think of the children. You clearly are not. In Europe, the Little Ice Age represented a .5C-.8C drop in temp (from the Medieval Climate Anomaly). It was not pleasant for the children of Europe. Rapid climate change is never pleasant for children, because it usually puts a strain on food supply. Why, you might wonder, did humans evolve agricultural civilization over the past 10k years instead of some other 10k year period? It's not like we haven't been smart enough. Indeed, a recent study concluded that we've become worse at problem solving over the last 10k years. So what was it? Try climate stability. The Holocene has been remarkably stable, as interglacials go. Human cultural memory, in fact, assumes a stable climate. There are no representations of persistent instability of the type that occurred during glacial periods and previous interglacials. We assume a stable climate. We have trouble imagining anything else. Even when we imagine it--with the help of science even--it's still so unreal that we can't imagine the full range of everyday consequences. Writers have tried. We're going to get persistent instability for quite a while, dan. If we de-fund education, then we de-fund the means of thinking through the persistent change. You perhaps imagine a world where we drop back and rely on conventional wisdom with regards to the weather and agriculture. No. Weather is changing, and it is not changing from one regime to another. It is persistent change. All systems are changing: climate is everywhere. If you de-fund education, you blind the world just as it is walking across a period that, metaphorically, is the top surface of a glacier. Of course, we may be blind already, since the "brains" of the world, the political guidance, do not believe their "eyes." Oh, and dan, imagine living your life according to the comet theory: at any point, a stray bullet could come through the window and kill you. Why do anything? Why post your comment?
  9. human agricultural civilisation was the worst development in our history and the beginning of the splintering of our psyches, the start of war and teritorialism, in turn monarchies, and the large scale oppression of human subjects. Hunter gatherers live in complete harmony with their environment, taking only what they need. Not like modern capitalsitic practice of over supply of mcdonalds beef burgers.whats more, recreation time lead to crackpot theories of gods and the like and more recently the splintered sciences hypotheses. what are they all observing their own little fragmented view of inconsequentiality. Its like in my city, christchurch which had an earthquake. the scientists can only study the after effects, and they get funding for doing that? unbelievable. whereas we had a moon man who studies the cycles of the supermoons and he actually predicted a big one was coming, the scientific community was upset about it but why can't the moon effect things. last time i heard its the only reason earth is inhabitable due to axis for seasons to be temperate. people cant see the wood for the trees. theyre observing things but understanding little. media is a sensationalist scaremongering thoughtless behemouth.start a fire in your backyard and reconnect with the primitive beast.
  10. Ah dan, such romantic notions... Back to reality. Physics says that the moon's effects are insufficient to drive large geophysical events, though you're right that we should be grateful to the Moon for stabilising Earth's axial tilt. But crackpots like Ken Ring prey on the superstitious and gullible to garner a little fame for themselves. Don't fall for the astrologers! Real-world geophysical events are not controlled by the Moon, but by much larger forces - motions, stresses and sources of heat within the Earth. And don't be afraid when the Moon is a wee bit bigger in the sky due to entirely normal and predictable occurrences of lunar perigee. One happened on 14th November during the total eclipse - it was the reason the Moon was big enough to cover the Sun for a beautiful, utterly predictable event. Another will happen in about nine days time, when the moon will be an unspectacular waning crescent in the dawn sky. In fact, 12 have come and gone this year! About once a year, the media gets all excited because perigee roughly coincides with a Full Moon, leading to the so-called "supermoon" (really, nothing special, though some decent spring tides). Do yourself a favour, dan, and ignore the astrologers like New Zealands woeful Moon Man.
  11. Dan, depending on one's understanding of utilitarianism, one can argue either that ag civilization is more horrible because it brings misery to more individuals (in sheer numbers), or one can argue that the preceding h-g cultures caused more misery because lifespans were shorter, survival was much more in doubt for a given individual, and individual freedom was extremely limited. I disagree that ag society brought wars of territory and economy. I argue that climate stability brought those features. A long, warm, stable climate allowed territorial expansion and population growth. Eventually, h-g groups would have started to bump into each other, as they undoubtedly did during the glacial periods. Ag culture simply speeded up the process. Ag culture also allows the development of science, which gives us the chance--the chance--to become responsible about what happens next. dan: "start a fire in your backyard and reconnect with the primitive beast." Ok, but later on in the evening I'll come back to the internet. The more we disconnect with each other, the more willing we are to cause others pain and misery. If science and then engineering can force us to look into each others' eyes while we have our fingers on triggers (literal or metaphorical), then I'm all for it. If seven billion people go primitive right now, six billion die within two years.
  12. skywatcher @ 335 You said
    Real-world geophysical events are not controlled by the Moon, but by much larger forces - motions, stresses and sources of heat within the Earth.
    I seem to remember reading that the tidal stress of the moon's gravity acting on our rocky planet generates some of the heat in our core, so some earthly geophysical effects may be contributed to by this influence. Certainly not by the phases of the moon, but could lunar perigee/apogee gravitational differences be enough to have an effect on Terra? I doubt it.
  13. Doug H @337, tidal stress accounts for 0.0004 W/m^2 of the 0.09 W/m^2 geophysical energy from the Earth's interior, or just 0.44%. And yes, differences between Perigee and Apogee are irrelevant in geophysical terms, though not for oceanic tides. Consequently I believe skywatcher's claim withstands scrutiny.
  14. Thanks, Tom, that clears it up for me.
  15. I came across this article http://www.nature.com/news/polar-research-trouble-bares-its-claws-1.12015 about how crabs, which had been excluded from the Antarctic continental shelf for 30 million years because of the cold, are invading due to the incursion of warmer ocean waters. They are preying on an ecology that had evolved free from hard-shell-crushing predators. This is evidence that the current climate change is far beyond normal natural variation
  16. '....It is obviously true that past climate change was caused by natural forcings. However, to argue that this means we can’t cause climate change is like arguing that humans can’t start bushfires because in the past they’ve happened naturally...' is just another absurd comparision.

    Comparing a billions of years old eco system and it's natural forcings over eons, to e.g. two neanderthals rubbing two sticks together 10,000 years ago to start a fire, and then accidently starting a bush fire, (proving that even neanderthals had the ability to change the climate!) demonstrates (-snip-).

    Response: [DB] Inflammatory snipped. Please read this site's Comments Policy before commenting further (link adjacent to the comment box). Further comments constructed as this one will be deleted in their entirety. FYI.
  17. pcrudy...  It's actually a very apt comparison.  It's shown over and over in published research that CO2 is the "Biggest Control Knob" (as Dr Richard Alley puts it) for global climate change.  

    Essentially, what humans are doing is taking that knob, that naturally modulates, and we're turning it rapidly in the warming direction.  So, saying that natural climate change precludes humans being able to change climate is fundamentally wrong.  And that is the point of the statement.

  18. pcrudy:

    The comparison is quite accurate. Arguing that humans can't drive climate change now because humans didn't drive past climate change - in the face of basic physics, backed by empirical evidence, that they can and indeed are - is logically equivalent to arguing that humans can't cause brush fires because they didn't in the past.

    The scale of the behaviour being argued is not pertinent.

  19. Another aspect of the "climate has changed before" argument, not covered off in the current answer, is the implication that current climate change should not be considered alarming. "It's changed before, and yet here we are" may be a fair summary of this version.

    Is it worth adding some relevant discussion and cross-filing the argument under both the "It's not us" and "It's not bad" taxonomies?

    The main responses seem to me to be that a) deep past climate changes were not much fun for living things at the time, being associated with mass extinctions and great upheaval; b) human societies and economies are adapted to the climate they developed in, and so even changes within the range of natural changes of the distant past would be very disruptive; and c) humans now use a very high proportion of potential quality farmland, affordable freshwater and so on to accommodate a large population with high (for many) or rising (for many) living standards; there is not much safety margin  to prevent a loss of living standards if climate change erodes availability of some of the resources we depend on.

  20. What was wrong in what Richard Lindzen wrote?

  21. Mark @345 - there's nothing directly wrong with 'the skeptic argument' as articulated by Lindzen here.  It's the implication of the statement where the problem lies.  Saying 'climate has changed naturally in the past' is like saying 'humans breathe oxygen'.  No duh.  Everybody knows that.  So what's the point in saying it?  The answer to that question is pretty clear.

  22. Mark @345 - there's nothing directly wrong with 'the skeptic argument' as articulated by Lindzen here.

    So the "#1 global warming myth" is not really a myth at all...?

  23. Mark, "the climate has changed" before is mostly used to imply that humans arent responsible for current warming and/or that past changes are unforced. As a skeptic argument, it is framed as an excuse to do nothing. In the source where the quote came from, Lindzen tries to touch both bases, along with an a priori assumption that climate sensitivity is low. He has been trying to find some plausible reason for low sensitivity without much success so far. If you want to get down to real myths, then I guess you have to look at what logical step follows from "climate has changed before" but for many, this somehow seems to be enough.

  24. No.  There's nothing wrong with the information itself.  The myth occurs when the information is voiced--made public.  I'd bet you that in 99.99% of the cases in which those facts are strung together and published, the person doing the stringing is attempting to make an implied argument that since climate has changed before without rapid accumulation of atmospheric CO2, and therefore the current climate change is not the result of human CO2 emissions.  I've engaged with at least 400-500 people on comment streams using this very implied argument.

  25. So the answer to your first question is "What's wrong is that Lindzen actually wrote it."

    In other words, Lindzen thinks you're stupid or at the very least simply ignorant, and willingly so.  If you said to him "Duh! What's your point?"  he'd probably bluster a little and then show you some really cool graphs. 

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