Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


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.

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

Keep me logged in
New? Register here
Forgot your password?

Latest Posts


Climate Hustle

We've been through climate changes before

Posted on 9 March 2012 by Sarah

This is the basic rebuttal to 'Humans survived past climate changes'

Humans have been through climate changes before- but mostly cold ones and mostly in our far distant past.

"Yes, our climates change. They've been changing ever since the Earth was formed." Rick Perry

Previous major global climate changes were glacial cycles that happened long before human civilization developed.

The human species evolved during the last 2.5 million years. Our far distant ancestors survived through multiple gradual cycles of cold ice ages, but did not experience any previous "hot ages." 

We Homo sapiens in our current form appeared only about 200,000 years ago. So our species has survived two ice ages. In each ice age global temperatures were colder by 4 °C. The warmest period ever experienced by early humans was about 1 °C warmer (global average) than today. That period occured between the two most recent ice ages, 120,000 years ago (Eemian). Over the next 100,000 years temperatures gradually decreased into a new ice age. During that colder period humans began to expand out of Africa and across the globe. Ever since the Eemian much cooler temperatures have been the norm.


Image by John Garrett.

Human civilization is roughly 12,000 years old, as defined by the start of permanent settlements and agriculture. Agriculture became established as the glaciers retreated from the last ice age. Modern society has developed entirely in our current geological epoch, the Holocene. Global temperatures haven't varied by more than ±1 °C since. There have been regional shifts in climate (Medieval Warm Period, Little Ice Age, etc), but since civilization began humans have never experienced a hotter global climate than now. 

Going back further, over a million years or so, our pre-human predecessors experienced a series of long cold glacial cycles. Several short interglacial periods were as warm or slightly warmer than our current climate. For example, the climate 400 kyrs ago, was slightly warmer than now. But more typically for the last million years it's been 4 to 8 °C colder. Each transition from warm to glacial ages and back took thousands of years, giving humans and prehumans many generations to adjust. 

So, really, the climate hasn't changed much since we settled into towns, invented plumbing, and started calling ourselves civilized.

Since humans and our human ancestors have been on Earth, average global temperatures have never been 3 °C warmer than now. In the next 100 years our children will be the first people ever to experience that kind of climate.


But, perhaps Mr. Perry is thinking he'd like to live in a climate eons ago, closer to when the Earth was formed.

precambrian globe

Digging way back in time, we know that Earth's climate has certainly been very different than it is now: 2 billion years ago there was not even any oxygen in the atmosphere. 550 million years ago high CO2 levels caused extreme greenhouse conditions. Humans were not around to care; the most advanced life form at that time was a flatworm. Humans could not physically survive over most of the planet in the age of the dinosaurs (Cretaceous, 100-65 Myr ago). Only very small mammals were beginning to evolve. Global average temperatures were 10-12 °C hotter than today. Most places on land were so hot that humans would risk fatal heat stroke every summer.


The geological record shows many ancient changes in climate, including massive ice ages, hot-house conditions, oxygen-free and acidic oceans, and massive extinction events. These changes happened millions of years before humans, most occurred before even primitive mammals, appeared on the scene. Previous climate changes were caused by orbital wobbles, solar fluctuations, and movement of continents. None of those effects are causing the current heating


References (added 2012-03-11)

Breecker, D. O., Sharp, Z. D., & McFadden, L. D. (2010). Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100. Proceedings of the National Academy of Sciences, 107(2), 576–580. doi:10.1073/pnas.0902323106.

Ron Blakey, Global Paleogeography maps:

Glikson, A. (2008). Milestones in the evolution of the atmosphere with reference to climate change. Australian Journal of Earth Sciences, 55, 125–139.

Hansen, J. E., & Sato, M. (2011). Paleoclimate Implications for Human-Made Climate Change. Arxiv preprint arXiv:1105.0968.

McInerney, F. A., & Wing, S. L. (2011). The Paleocene-Eocene Thermal Maximum: A Perturbation of Carbon Cycle, Climate, and Biosphere with Implications for the Future. Annual Review of Earth and Planetary Sciences, 39(1), 489–516.  Annual Reviews. doi:10.1146/annurev-earth-040610-133431.

Sherwood, S. C., Huber, M., (null), & (null). (2010). An adaptability limit to climate change due to heat stress. Proceedings of the National Academy of Sciences of the United States of America, 107(21), 9552–9555. doi:10.1073/pnas.0913352107.

Ulrich C. Müller, (2009) "EEMIAN (SANGAMONIAN) INTERGLACIAL". p 302, inEncyclopedia of paleoclimatology and ancient environments editor, Gornitz, V. Springer Verlag.


0 0

Bookmark and Share Printable Version  |  Link to this page


Comments 1 to 40:

  1. I don't think it is chance that agriculture and civilization developed in the first interglacial since the development of human language. There is indirect evidence of that occuring about 80,000 years ago.

    I would be hard to develop civilization during a glacial though once developed it could survive.
    0 0
  2. The global climate and human evolution graphic is an excellent teaching tool. The whole post is clear, uncluttered and easy to digest. Thank you, Sarah.
    0 0
  3. This post has good features as Doug says. But the paleontology paragraph provokes some quibbles:

    The age of dinosaurs started sometime in the Triassic.

    Size of cretaceous mammals - not alway so small:
    "The entire body of IVPP V14155 is more than one metre in
    length (skull, 160 mm; trunk, 522 mm; preserved tail, 364 mm),
    comparable to that of a large Tasmanian devil12."

    toward the end of the cretaceous some other mammals were near this size - i can't recall their names and I think their lineages became extinct.

    When did mammals "start to evolve" if one can use that phrase? One might say with the first synapsids, well before the Age of Dinosaurs.

    Oxygen inthe early atmosphere:

    came up to around 1% a few hundred k years of the start of the "great oxygen event"

    Was the climate suitable for human survival in the mesozoic? Sure, near the poles when the tropics were too warm.
    0 0
  4. Lloyd Flack @ 1: no, it wouldn't be that hard to develop a civilisation during a glacial - just not in the northern climes where modern civilisation flourished. Some other areas of the planet might have had quite agreeable climates during the glacial periods.

    Take this paper for example:
    New Light on Human Prehistory in the Arabo-Persian Gulf Oasis.
    There's a less technical take on it in this article, and plenty of other articles online too.

    On the other hand, this hypothesis also gives a great example of the possible consequences of global warming. Sea level rise at the end of the last glacial completely wiped out the civilisation in question, submerging their towns & villages, farmland, and hunting lands, turning their entire population into refugees (and quite possibly inspiring the legend of the biblical deluge in the process). It's a salutary warning of what might happen to significant chunks of our civilisation if the great ice sheets melt.
    0 0
  5. It wouldn't be difficult to cause an anthro-uproar about when civilization began - it depends on the criteria. 10,000BC, around the Catal Hoyok period is as good as any. The Levant agricultural rise during the Younger Dryas was both a precursor and a partner. It was a jerky, halting, rise-n-fall process until the printing press. From start to recent times, the huge swings in climates have been contained inside about a 1dC global change-range, and regional climate changes rarely spread around the globe. This interglacial was already an anomaly before AGW (and that anomaly may be the foundation stability that is the bedrock of our civilizations).

    The difference with the current challenge starts with the soft-sell phrase "climate change". Gribbin stood it up more accurately when he called it Hothouse Earth. 'The Polluted Planet', and 'Garbage Dump Earth', might push some of the smarmy-warmy-fuzzy sugar ('but the climate has always been changing') off the podium (Mr. Perry goes here).

    And the climate disruption is only one aspect of the shift - ocean acidification, extreme events, and bio-degradation are indivisible elements of the pollution-problem web.
    0 0
  6. The early Earth atmosphere had no or very little oxygen, don't fancy living in that. A really good TV series that investigates the development of life on planet Earth is the BBCs 'How To Grow A Planet' presented by Prof Iain Stewart. It shows how plants developed and changed the planet in a dramatic way.
    0 0
  7. I recommend that the instant, snappy, response when someone says,"...oh, the climate has always changed!", should be "...sure -- but not while civilised humans have been around!". Then if you get the opportunity to continue, go on to say, "...history suggests that a stable climate is necessary for a stable civilisation; that's why by changing the climate today we're playing a dangerous game that risks all the benefits of living in a civilised society".

    In my experience, in a verbal confrontation, this response works well with both the initiator and onlookers. You've not undermined your opponent, but you've just suggested that it's a lot more complex than the original bare denial statement would suggest. It's more difficult for them then to backtrack. It also makes it more difficult for them play the old " greens want us all to go back to the Stone Age", meme; as you can say, "No, by preventing climate change we're trying to stop society reverting to the Stone Age."

    I hope that helps. 'Climate's always changed' is such a common meme that it's worth memorising the snappy one line response. As we all know; it's rare that we can have a rebuttal which can be as short as the meme.
    0 0
  8. "Global average temperatures were 10-12 °C hotter than today"

    I believe that should be °F (see e.g. here).
    0 0
  9. We are going well outside anything homo anything has experienced. CO2 has not been this high in the time of man.
    0 0
  10. "Yes, our climates change. They've been changing ever since the Earth was formed."

    Or like the defendant of the serial killer: "Yes, they died. People die ever since they appeared on Earth."
    0 0
  11. I was wondering if someone might explain why these periods of glaciation took place? Volcanoes? Vegetation sequestering CO2? Asteroid impact? Why? Just curious to know, thanks.
    0 0
  12. Do you mean the cycle of glacial and interglacial periods or the fact that we have an ice age containg these periods.

    The fact that there is an ice age is beieved to be a matter of continental configuration and CO2 levels. We have an ice age when warm currents can't get to the poles and CO2 is low enought to allow an ice build up.

    The glacial-interglacial cycle is believed to be controled by thre Milankovitch cycles, cycles in Earths orbital and rotational parametters. Thes affect the distribution of radiation recieved by the Sun. How much Summer sunlight is recieved in high Northern lattitudes seems to be what is important. This is greatly amplified by the albedo changes from glaciation and the sequestration of CO2 in the ocean as temperatures fall.
    0 0
  13. @11

    Milankovitch cycles
    0 0
  14. "Human civilization is roughly 12,000 years old, as defined by the start of permanent settlements and agriculture. ... Global temperatures haven't varied by more than ±1 °C"

    This is a key point that buffoons like RPerry do not and cannot comprehend. Prior 'natural cycle' climate changes have not required much in terms of a global temperature change.

    There are many versions of this type of graphic floating around. It defines our very narrow (+/- 1C)'comfort zone.'


    Anthropocene climate change will push us out of that comfort zone, much to our peril.
    0 0
  15. Indeed. We are probably looking at something like PETM II (a sequel, not a remake, more abrupt onset and other diffs). I wonder how our agriculture will do under a PETM-like climate.
    0 0
  16. Thanks, Sarah ... this is just a super nice addition to my public lectures for "normal citizens" in our local area near Hannover, Germany, which I will give coming May ... but also lot of comments are very useful with all their knowledge and graphs ...

    The paleoclimate is one of the "Tummelplätze" (German for "play areas") for our friends the denialists ...
    0 0
  17. One must be careful with global averages.

    During the Holocene Climatic Optimum, global annual average temperatures may not have varied much from average. But that does not mean significant variation did not occur.

    But orbital variation meant for the Northern Hemisphere, longer more intense summers and the same duration but more intense winters.

    Conversely, southern summers and winters were more moderate.

    Were winters ten degrees colder and summers ten degrees hotter, the average might be the same, but the climate would be much more extreme.
    0 0
  18. Chris G at 05:31 AM on 10 March, 2012

    More abrupt indeed. PETM took a time of the order of 10,000 years to warm some 6ºC. Now we're talking about the potential of warming as large as that, happening in one or two centuries.
    0 0
  19. Unless we push the climate to a Venus like state, it is pretty certain we will survive as a species. It will be like the Roman Empire collapsing times two orders of magnitude. Our great great grandchildren will have Atlantean type legends of these god like beings that could talk to people on the other side of the world, that flew to the moon and who actually turned rock into metal. Science fiction keeps coming true.
    0 0
  20. @19
    It is impossible to push the Earth's climate to a Venus like state.
    0 0
  21. An impact powerful enough to vaporize all the world's oceans would do it, but I don't think it is possible to do it just with co2, and civilization would collapse long before. I think civilization could collapse as soon as 2100. Most major cities around the world are close to sea level.
    0 0
  22. Thanks John Russell @7 four giving us verbal strength in dealing with denialists. There is a saying "don't cut the branch on which you're sitting", invented I guess by loppers. It's becoming obvious that the "civilisation" is doing that by mining and burning fosils and altering the carbon cycle in unprecedented manner.

    The problem of altering carbon cycle with consequence of AGW is just one example. Another is land use change, forest destruction, chemical contamination, which all contribute to alteration of environment and ongoing mass species extinction. Overuse of DDT was one example. Coal Seam Gas mining is another emerging example (both chemical contamination and carbon cycle alteration is involved here).

    Until the economical balance of so called "civilisation & proggress" does not include the environmental sustainability, mankind will continue "cutting the branch on which it's sitting"
    0 0
  23. Lucas Verma#17:

    "During the Holocene Climatic Optimum... for the Northern Hemisphere, longer more intense summers and the same duration but more intense winters.... southern summers and winters were more moderate."

    Do you have any references to support this?

    "Were winters ten degrees colder and summers ten degrees hotter..."

    Do you see a mechanism that results in this combination?
    0 0
  24. "Humans survived past climate changes".

    Well, no, not really.

    Our "cousins" the Neanderthals didn't survive the last ice age.
    0 0
  25. @19 Yes, we will survive as a species, but our near descendants will live in such misery, they will wish we had not survived. And those cultures that still practice ancestor worship (think China) will replace it with ancestor cursing if they preserve just enough scientific knowledge to understand why they are suffering so.
    0 0
  26. The article is a good article, true, but there are a couple small points that if addressed would make it even better, and that by a lot.

    1) Homo Sapiens should be capitalized throughout 2) the text would be a lot easier to follow if it did not appear to contradict the graph: just eyeballing the graph, it looks like the highest temperature WAS the peak near 120,000 before present, while the text gives an earlier date for a higher one. this suggest 3) the diagram would be greatly improved if there was some indication of the vertical temperature scale. 4) lose the sarcastic line about what Perry would prefer. That really does not help make the case at all. We all know Perry is a Creationist too.
    0 0
  27. MattJ, the Eemian interglacial, the peak near 120,000 before present, *was* slightly warmer than the Holocene by ~1-2C, CO2 was slightly higher than pre-industrial Holocene CO2 (~300 vs ~280), and sea level was ~4-6 meters higher as well.

    But the current CO2 level of ~390 ppm is higher than at any time since the mid-Pliocene, when it was 2-3C warmer than today and sea level was ~25 meters higher.
    0 0
  28. While this article deals with Texas Gov. RPerry's delusions, it is worth noting Oklahoma senator James Inhofe's latest take:

    Senator James Inhofe (R-OK) appeared on Voice of Christian Youth America’s radio program Crosstalk with Vic Eliason yesterday to promote his new book The Greatest Hoax: How the Global Warming Conspiracy Threatens Your Future, where he repeated his frequent claim that human influenced climate change is impossible because “God’s still up there.” Inhofe cited Genesis 8:22 to claim that it is “outrageous” and arrogant for people to believe human beings are “able to change what He is doing in the climate.”

    If you have difficulty believing your eyes, you can listen to the great man making his case.
    0 0
  29. Following on points by william-19 and Chemware-22: the hit on our living standards is exposure one. It's already adding to taxes and insurance premiums (extreme events rising in number and rising faster in damages).

    Weather pattern instability is already increasing. So the second hit will be on aqua&agriculture - basically, the things that can't move and that driver producers out of business.

    Any idea that the damage stops if the pollution is stopped is expecting a runaway train to stop at the flip of a switch. While the species can survive, it will become impossible to support 7 billion-plus inhabitants; the forecast of double that by mid-century shows hit three - population upheavals and crisis. It took politics, religion, civil war, AND drought - to produce the South Sudan Drought.
    0 0
  30. Do we not need to see some researchers come up with a global heat index history of the planet of the last half-century or the last century, to go along with the actual global temperature history?

    And with this, also a comparison of daytime and nighttime global heat indexes to go along with the same for actual global daytime and nighttime temperatures. (Is it not so that the global nighttime heat index going up faster than the global daytime heat index would be as powerful as the global nighttime temperature going up faster than the global daytime temperature as evidence for a powerful increase in greenhouse gas activity? No other method of heating can cause these diurnal range decreases that have occurred as they have occurred.)

    The heat index measure (temperature and relative humidity) may be much more important than mere temperature as we go forward.

    That is, with ever-increasing global water vapor, since eventually it's harder to get temperatures as high when there is more and more water in the atmosphere compared to when it's dry, should we not expect eventually a slowdown in actual global temperature increases but no slowdown in global heat index increases?

    And the heat index is much more relevant to survivability for animals like birds and mammals - see the warnings of such studies as that study published by the National Academy of Sciences (NAS):

    "An adaptability limit to climate change due to heat stress"

    This NAS research says that even with just an eventual 5 degree C global temperature increase down the road (they looked at both a 5 degree C and 10 degree C increase), smaller and then larger parts of the planet will become uninhabitable because of non-survivable summertime heat indexes. (They are talking heat indexes not seen for tens of millions of years, before modern birds and mammals evolved and covered the planet as it cooled over those millions of years.) A 5 degree C increase would stress human civilization to a breaking point. And if an eventual 10 degree C global temperature increase happens somewhere down the road, half the planet would probably become a dead zone in terms of bird and mammalian life, and present civilization could not survive. One reason for this last point is simple - the land mass that would be left as habitable could not support the many billions population that will obtain this century. There would have to be a reduction of many billions. Just think the implications through.

    See what the researchers themselves say about their own research in terms of the heat indexes, directly and indirectly:

    Quote: ""The wet-bulb limit is basically the point at which one would overheat even if they were naked in the shade, soaking wet and standing in front of a large fan," Sherwood said. "Although we are very unlikely to reach such temperatures this century, they could happen in the next.""

    Quote: ""Most people are more familiar with the heat index, or the feels-like temperature they see on the weather report. The wet-bulb temperatures we are talking about would have a feels-like, or heat-index, temperature of between 170 to 196 degrees Fahrenheit," Huber said.

    In line with this NAS-published research: By this online heat index calculator

    a temperature of 100 degrees F with a relative humidity of 75 percent gives a heat index of 150 degrees F, and a temperature of 105 degrees F with a relative humidity of 75 percent gives a heat index of 176 degrees F. The former would kill many humans and other modern birds and mammals within hours, and the latter (the lower range of a wet bulb temperature of 95 degrees F) would kill all humans and probably all other modern birds and mammals within hours. (Don't dismiss this. Don't forget that air conditioning can go out and power failures can occur, and so on.)

    Do we not need to care about the future of our planet and the life on it, and care what heat indexes the middle parts of our planet will be experiencing throughout the next couple or few short centuries during summertime heat waves, as the globe accumulates more and more heat energy?
    0 0
  31. muoncounter @ 13:10 PM, what will the Inhofe's of this world do when the climatic changes become undeniable? When the CO2 levels hit 500ppm, when the wheat fields become barren, when the sea level rises, when the Arctic is ice free, when human population becomes unsustainable, will they say "It's not us, it's God and He knows what is good for us"?

    Wilful blindness in legislators does not make for good legislation.
    0 0
  32. MattJ, as a matter of taxonomical convention, the one instance of Homo sapiens in the article, if written correctly, would be written as I have done in this comment.

    Minor nitpick of a nitpick...
    0 0
  33. In the near term there is adaptation. Humans are not cattle but some of the same principles apply, such as cooling, diet and genetic alterations. The long term is 100% speculation. I could equally well argue that technology will allow humans to live comfortably in 130F desert or in high heat indexes or in -70F Antarctica.
    0 0
  34. Eric,

    Eventually yes, but will technological changes arrive in time to prevent massive harm. There is a saying "Don't schedule breakthroughs."
    0 0
  35. Eric writes:
    "I could equally well argue that technology will allow humans to live comfortably in 130F desert or in high heat indexes or in -70F Antarctica."

    True, given sufficient energy. There's the rub.
    0 0
  36. I'm looking for a good, recently published N.American paleoclimatology book; one that focuses on the late Pleistocene and Holocene. I read through the Desert's Past (Paleoclimates of the Great Basin) and found oodles of good information there, but not so applicable to my region.

    I work in SE Texas and apparently during the Holocene Optimum we experienced a significantly different climate; one that was at least drier if not warmer, or at least more prone to long drought. Unfortunately our surface sediments are muddled enough by ubiquitous burrowing rodents and tree throws leading to argument on what really lead to today's land forms. Further, human action could have caused much of what we see in palynological studies so I'd like to read up on what solutions a broader study on N. American Holocene climatology has to offer.

    If the Texas H. Optimum climate was what I think it was, and if we are facing a similar climate (or maybe already), then we have some unpleasant suprises awaiting us.
    0 0
  37. Andrew Sipocz

    I read somewhere a while ago, but can't confirm this, that significant parts of the US Plains States were once desert. That features like the South Dakota Badlands were once sand dunes and that explains the geology/topography of the region. Rolling hills that are actually old sand dunes, where when the surface gets broken through, erosion of the old dunes then causes features such as the Badlands.
    0 0
  38. This is the first article I've read on Skeptical Science. I was tipped off to its potential interest by Joe Romm on his Climate Progress blog. I was delighted not only by the interesting article but also by the intelligent, frequently informative comments. How different from the comments I usually see (for example at the Scientific American web site) posted after articles dealing with climate change! Congratulations to Sarah and to all commenters!

    I want to echo MattJ's (#26) suggestion: Sarah's article would have much greater impact on scientifically trained readers if its graph showing global temperature fluctuations for the past 750,000 years had a properly labeled vertical axis (showing the magnitude of the temperature changes in degrees C or F). I hope that Sarah will update her article with such a modified graph.
    0 0
  39. Thanks for the comments, and welcome to visitors from ClimateProgress.

    I've added a list of references which can answer many of the issues raised above.
    The temperature data on John's image can be found in the Hansen and Sato paper. I'll check with him about adding a T scale.
    0 0
  40. Interesting programme on Channel 4 regarding climate change and early Homo Sapiens. Tony Robinson relates how the last great warming cycle 130,000 years ago saved early humans from extinction. The population at that time was about 10,000 and falling and clustered around water holes. But the end of that particular cold spell ended the drought in East Africa and allowed the population to expand across, and out of Africa. He discusses how major climate change have effected humans in the past, how we have adapted, and how the current climate change will have unknown impacts on us as a species. Uncomfortable viewing for some, but fascinating all the same.
    0 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2019 John Cook
Home | Links | Translations | About Us | Privacy | Contact Us