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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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Comments 751 to 800 out of 826:

  1. @ 750 MA Rodger

    WOW MA Roger what would I do without your knowledge and brilliance?

    I immensely thank you for your response!

  2. Here we go! My favorite denier is back to attacking me.

    Why don't you tell us about the severe weather up through the 1700s? Oh, that's right, you can't, because nobody recorded it.

    I'm guessing you're totally oblivious to the fact that the Romans grew grapes in Britain and made wine. The Emperor Hadrian was drinking and enjoying that wine.

    I responded with a NOAA link that stated.

    Clues about the past climate are buried in sediments at the bottom of the oceans, locked away in coral reefs, frozen in glaciers and ice caps, and preserved in the rings of trees. Each of these natural recorders provides scientists with information about temperature, precipitation, and more. Many of these have some type of layers, bands, or rings that represent a fixed amount of time, often a year or growing season. The layers vary in thickness, color, chemical composition, and more, which allows scientists to extrapolate information about the climate at the time each layer formed.

     

    Response:

    [PS] Desparation to be retreading that old one. Try here.

  3. What does wine making in England have to do with anything? The Romans brought it to England, so what? They liked it, and it was unknown there until then. The climate made it possible, although never ideal. It was cultivated in England almost without interruption until the tax laws of the 19th century discouraged production, and later WW1 activity demanded the land. It was cultivated throughout the so-called little ice age as well. What does that show? That England's climate was stable for about 2000 years. Big deal, like we didn't know that.

  4. England's climate today is far more conducive to growing grapes for the wine industry than at any point in recorded history.

    I'll post the links tomorrow.

     

    Your denier is clearly desperate and unencumbered by an education in the science in question.

  5. @ [PS] LOL that's a new one on me. I had never heard of it so it must be a desperate attempt by this denier!

    @753 Philippe Chantreau

    I thought the same thing...what the heck does wine making in England have to do with anything. Glad to be able to expose this denier as he's been commanding the stage for quite some time as if he's some sort of expert! *rolled eyes*

    @ 754 Daniel Bailey

    Agree his house of cards has been slowly tumbling down since I arrived to "educate" him.

     

    Thanks everyone I've been learning a lot from you all!

  6. Here's those details and links on vineyards then vs now:

    While England had 42 vineyards at the time of the Domesday Book, as is well known, there are now over 300 commercial English vineyards today. So the climate today in England is much more conducive to wine-making than during the Roman occupation of England.

    http://www.english-wine.com/vineyards.html

    "It is generally agreed that the Romans introduced the vine to Britain. It has also been inferred that the climate in Britain at that time was warmer. At the end of the first century AD, however, the writer Tacitus declared that our climate was “objectionable”, and not at all suitable for growing vines.

    Today, there are vineyards in nearly every county of England and Wales, and there are vines now planted in Scotland. Much of the acreage and vineyards lie in the southern part of England, and more specifically Kent, Sussex, Surrey and Hampshire. Those few hundred acres first planted has now grown to over 5,000. In the last ten years alone, the acreage planted has more than doubled, and nearly tripled since 2000. Last year, around 1 million vines were planted – the highest planting in a single year, and perhaps a higher volume is set to be planted in 2018. All of this will lead to some substantial increases in production."

    Emphasis and underlining added.

    https://www.winegb.co.uk/visitors/background-info/history-of-the-industry/

    By 1977, there were 124 reasonable-sized vineyards in production – more than at any other time over the previous millennium. The website of the English wine producers suggests that at present extent of vineyards in Britain probably surpasses that of the Medieval Warm Period between circa 900 AD to 1300 AD.

    http://www.realclimate.org/index.php/archives/2006/07/medieval-warmth-and-english-wine/

    New Scientist Link

    Warmer now

    https://www.eh-resources.org/historical-climatology/

    In case anyone was wondering about Vikings and vineyards:

    Let me…assure you that the last wine plants to grow in Greenland were those that grew…60 million years ago.”

    LINK

  7. @ 756 Daniel Bailey

    Thank you!

    Is our current Holoceen cooler than previous interglacial periods...thus there is nothing to worry about? A denialist posted this.

    From my understanding we should be in a cooling era but as we all know we are in a warming era.

  8. Current peak global temperatures have already exceeded those of the Eemian OR the Holocene, looking at the land station data (red):

    Modern warming warmest in 126,000 years

    http://www.columbia.edu/~mhs119/Temperature/T_moreFigs/

  9. Since the peak temperatures of the Holocene 7,000 years ago, global temperatures naturally cooled 0.8 C.

    Over the past 100 years, the warming from human activities has warmed the globe 0.8 C, utterly erasing that natural 7,000-year cooling.

    With plenty more warming to come.

    Last 20,000 years

    Bigger image here.

  10. Thank you so much Daniel Bailey!

    A denier is claming these things:

    The irrefutable scientific evidence is that Earth is always warmer and wetter, never warmer and drier. That will increase the amount of arable land and also increase food production. That's good news for farmers in foreign States, but not good news for American farmers who will have difficulty competing globally.

    The irrefutable scientific evidence also shows that in all 8 recorded Inter-Glacial Periods, the sea levels rose 3 meters to as much as 14 meters, even when CO2 levels were 260 ppm to 280 ppm CO2.

    So, whether CO2 levels are 260 ppm or 400 ppm makes no difference, because the sea levels are going to rise 3 meters to 14 meters no matter what happens.

    Are these claims accurate?

  11. Also is this accurate?

    Antarctica was warmer 1,000 years ago, long before the industrial revolution and before there has been an increase in CO2 attributed to man.

  12. I'll have more to say tomorrow, but as a preliminary answer, you're chasing the dog's tail.  Stop.

    Demand evidence for their claims, including source citations.

    Pretty much every single item you quoted is a baldfaced lie or untruth.

  13. He claims to have irrefutable evidence.

     

    Make him damn well show it.

  14. @ 762; 763 Daniel Bailey 

    Done!

    I look forward to your responses!

    Thank you!

  15. Warmer and wetter is true - CC relation requires it. However, the very broad pattern (with lots of regional exceptions) is that the wet get wetter, dry get dryer. There is no guarantee of more arable land where you want it. Does mean he now accepts global warming? More like "I will believe any nonsense that can justify sitting on our hands". More likely latter and as we said before, you are wasting your time.

    Warmer in Antarctica 1000 years ago? Umm, let's see that evidence.

  16. And for science - eg observations and models, try here. The Palmer drought index looks at both precipation and evaporation.

    However, I doubt your denier will open any evidence that might contradict what they would like to believe. If someone isnt prepared to let data inform their opinion, then it isnt worth arguing.

  17. TVC15 @760/761,

    It is a smorgasbord of denialist assertions you present.

    ☻ The "Antarctic was warmer 1,000 years ago" assertion looks a little difficult to uphold in any way. There are reconstructions from ice core data (for instance Ciais et al (1994) fig 7) which shows Antarctic temperatures over the last 10,000 years waggling about by a maximum of about a degree centigrade. (Note the Ciais et al graphic is sensibly using an 'average-over-the-last-5,000-years' as a datum.) The thermometer record (eg Berkeley Earth) shows recent warming of a similar amount (although there is a lot of variability in the warming depending where you are in Antarctica) so this evidence suggests it was colder in Antarctica 1,000 years ago. The image below is gleened from a posting on the planet Wattsupia and appears to be based on data from Marcott et al (2013). The 1,000 years ago temperature again is shown as being colder.

    Antarctic holocene temperatrure

    ☻ The interglacial sea level has been discussed before, introduced up-thread @715. It was shown that only two of the last 8 interglacials had higher SLR than today, not all eight. The SLR will mainly depend on how much of Greenland & Antarctica melts out, a process that stopped in this present interglacial 8,000 yers ago, and AGW is the process that is doing that melting today.

    ☻ The "Earth is always warmer and wetter, never warmer and drier" assertion isn't correct. The missing word word is 'atmosphere' which will be, as scaddenp @765 points out, wetter under the CC relationship. So if we have more wet in the atmosphere, will that translate firstly into more rain always falling on the earth beneath. Globally apparently not. This NOAA graphic shows global temperature and global rainfall are not well aligned. (The graph is from here and is for precipitation over global land)

    Global Land precipitation anomaly graph

    And secondly, as scaddenp @766 describes, even if rain and temperature were inexorably linked, that warmer atmosphere is demanding to be always wetter than it was when cooler and will thus be sucking more moisture right out of that very same land to re-charge its wetness.

     

  18. Here's a question I've often thought of related to past climate... In periods of a hothouse Earth, like the cretacious, what would the weather have been like? All we ever see are illustrations of dinosaurs in lush tropical landscapes. There would have been a helluva lot more energy in the climate system and so many more extreme weather events.

  19. I'll address a portion of that, now that scaddenp and MA Rodger already weighed in on the rest.

    "The irrefutable scientific evidence also shows that in all 8 recorded Inter-Glacial Periods, the sea levels rose 3 meters to as much as 14 meters, even when CO2 levels were 260 ppm to 280 ppm CO2."

    Again, saying that there is irrefutable evidence pretty much ensures that he's making that claim up.  If he had such "irrefutable scientific evidence", he'd have cited it.

    Part of the fallacy on display here is the presumption that interglacials are interchangeable and equal.  They are not.  They are the confluence of orbital factors and the "memory" of the climate over time (climate memory has been demonstrated to extend some 800,000 years or more, depending upon the metric in question).  A consilience of studies point out that the best analogue for the modern Holocene Interglacial is MIS (Marine Isotope Stage) 19 (per Giaccio et al 2015, Yin and Berger 2015, Vavrus et al 2018, etc).

    Looking at the 5 most recent interglacials, we see that sea levels are not identical (from Grant et al 2014, Figure 2):

    Grant 14, Fig 2

    From Dutton et al 2015, Figure 1, we see that sea levels from previous interglacials are tightly tied to temperatures...and we know from innumerable studies that global temperatures are tightly intercorrelated with atmospheric carbon dioxide levels:

    Dutton 15, Fig 1

     However, emerging evidence (from Grant 2019) for that Mid-Pliocene sea level on the very right-side of Dutton 15, Figure 1 above is that sea levels associated with an atmospheric composition of carbon dioxide like today saw a contribution of about 20 meters just from the Antarctic Ice Sheet by itself.  I believe Rob DeConto is coming out with a similar paper soon on that subject.

    Grant 2019, Fig 6.10

    Figure 6.10 The Whanganui RSL record on the left with the precession-paced MPWP and obliquity-paced late Pliocene sections highlighted with different GIS, AIS and NHIS configurations and SLE illustrated for interglacial and glacial extreme conditions relative to present-day Antarctica (0 m; central figure). The anti-phased 15 m amplitudes of the MPWP are interpreted as 5 m from GIS offset by ~20 m from AIS present day to peak interglacial. Higher amplitudes would then include larger-than-present AIS (nearing LGM; Clarke and Tarasov, 2014). While the late Pliocene amplitudes include increasing NHIS contributions and smaller interglacial configurations.

    To sum for this portion, previous interglacials are as unique as are your fingerprints, but contain similarities constrained by physics, with sea levels of the time correlated with global temperatures and atmospheric carbon dioxide levels.

    At present, the human burning of fossil fuels is driving an atmospheric composition and temperature associated with a time when sea levels were over 20 meters higher than at present, imperiling coastal port cities around the world and threatening areas where over 2 billion people currently live.

  20. Thank you, scaddenp, Daniel Bailey and MA Rodger!

    I'm with scaddeep's statement: "If someone isnt prepared to let data inform their opinion, then it isnt worth arguing".

    I realize how utterly useless my efforts are in trying to help the "deniers" understand the science that supports human caused climate change.

    I have learned so much from you all when I post the denier claims. I thoroughly appreciate the responses as you provide me with insights that I would not have been able to discover myself.

    However I've grown tired of dealing with the deniers. If they can't understand what they are seeing all over the globe right now as I type this there is no amount of science that will open up their minds.

    Here is just another sample of the type of denier minds out there.

    i have looked at a lot of evidence from both sides of the argument, and i dont need someone to tell me what my conclusions should be. and there is PLENTY of geological evidence that this round of warming is nothing more than a natural event, one that had been going on for the last 2 million years, ever since the north and south american continents collided. 100,000 years ago the arctic was ice free. and as has been noted many times by many people in many ways, here are a few truths you need to take into account;


    1: we are out of the last period of glaciation by only 15,000 years roughly
    2: the AGW crowd is complaining about an increase of 1 degree C over 150 years, but there is geological evidence that 15,000 years ago the temperature went up by something more like 10-15 degrees C in TEN years.(i didnt know there are that many SUVs back then, who knew?)
    3: we are still ten degrees COOLER than at this same time during the last intergalciation period, and the one before that, and the one before that for the last 2 million years. and its funny how the AGW crowd FAILS to take into account previous interglaciation periods, and what was NATURAL warming.


    and if you think that i am just being crazy, then why is the IPCC scientists solution always more regulations and more taxes and redistributing the wealth of the developed nations to those nations that are still developing? and why is it that all the so called climate change protocols penalize the developed nations, mostly western europe and the US, and ignore the rest of the world? why is china given a pass, along with india? two of the highest CO2 emitters in the world?


    if the AGW message was more consistent, and required ALL countries to stick to the climate change protocols, then perhaps their message might be more acceptable, and more people might actually listen to them.
    in the end these protocols are nothing more than a way for the UN to control the worlds population, and to work to usher in one world government with the UN running things, and no national sovereignty of any kind.

    now you claim i am a science denier, but that isnt the truth here. i suppose you also consider the science settled, and that is NEVER the case. the science is NEVER settled, except in the case of the closed minded, non scientific lemmings.

    I see no point in spinning my wheels on a mind such this.  

  21. TVC15 @770,
    Well, let that be a lesson for you!!
    Denialism isn't logical. It turns folk into swivel-eyed loons.

    To correct his nonsense-
    ♣ It was 3 million years ago (not 2) that North & South America collided and joined up, a process that did kick off the Arctic glaciation which then resulted in c3 million years of ice ages. And over tha last 1 million years the ice ages were significantly bigger. Presumably the present warming that is bringing this 3-million-year-period to an end can be blamed on the collision of the USSR and the Republic of China with the United States of America, these all constituting significantly large land masses.
    ♣ You probaly could argue the Arctic was ice-free 100,000 years ago but only through the peak of the summer melt season (as in the Arctic Ocean having the levels of summer ice we would declare today to be ice-free).
    ♣ 15,000 years ago we were still coming out of the last ice age. We were out nearer 10,000 years ago (as the graphed ice core data clearly shows).
    Ice Core Temperatures
    ♣ The extreme global temperature changes since the Last Glacial Maximum were nothing like "10-15 degrees C" except at a regional level (ie Greenland). And the period over which these increases occurred (the data graphed shows two large sudden Greenland increases in the last 20,000 years - +12ºC at 14.5kybp  & +9ºC at 11.5kypb - which were not 10-year periods of increase but 200-year periods. I don't think the ice cap volumes exist in the northern hemisphere to achieve a repeat performance today.
    ♣ The relative temperature of different interglacials has been discussed in this thread before and so we know the swivel-eyed loon is having difficulty hearing this particular message. So, yes, we do think he is "just being crazy" and that craziness is why he has such difficulty accepting the science and its implications.
    ♣ With regard to emisions controls, we can, of course, treat all people on Earth equally as the denialist wishes. The science says that anthropogenic CO2 emissions of more than 700Gt(C) will be bad and with 7.7 billion folk living on the planet, that would be an allowance of 91t(C) per head(historical) ('historical' as your allowance-use is handed down from previous generations).
    So let's calculate that allowance using Global Carbon Project figures and present-day population. Note these GCP territorial emission data only go back to 1959. Getting full historical figures would be possible (& correcting for increasing population could be factored in) but the general result will not change. That would mean that China still had an outstanding carbon allowance of 54t(C) per head, India 82t(C)/head while the good old USA has exceded its allowance and so has to pay back 238t(C)/head into the collective kitty. If full historical emissions were included, the US pay-back would be greater still, not qute as great as the UK pay-back if taken to the beginning of the Industrial Revolution. (From 1959 the UK pay-back is a trifling 47t(C)/head). Luxembourg from 1959 has a pay-bacl 0f 199t(C)/head but would be the country facing the biggest carbon-emissions pay-back with full historic figures.

    Denial is a sad thing to behold. Denialist folk become happy to dismiss the evidence witout any assessment of what they are ignoring. It is simply done. "The IPCC assessment reports? A complete pack of lies!!"
    More telling is the misuse of the remiaining information that you do accept. As you are ignoring whole swathes of actual data, your sources tend to be limited and adjusting the findings beyond that limited evidence becomes a necessity. So some, no all previous ice ages were warmer, golly, 10 degrees warmer, 20, 100 degrees warmer. We should be grateful we live now and not then!!!!
    And how does the following rate on the scale of untruthfulness given it comes from a real climatologist, abet a retired one. It's from Lindzen's seminar at the UK House of Commons in 2012. (@ 32.20mins in the first videoed part of his talk linked here. (You-tube link here)

    "Does it [20th century temperature increase] matter?"

    "Okay so some points to take away from the global mean temperature anomaly record. Changes are small. They are in the order of several tenths of a degree. Changes are not causal but rather the residue of regional changes. Changes in the order of several tenths of a degree are always present at virtually all time-scales. And obsessing on the details of this record is more akin to a spectator sport or tea-leaf reading than a serious contributor to scientific efforts."

    "Say, at least so far. I mean if some day I shoud see the changes are twenty times what I've seen so far, that would be certainly remarkable but nothing so far looks that way."

    The implication is that we have here a retired climatologist who considers a gobal average temperature increase of less than (0.7 x 20=) 14ºC to be unremarkable. Are we then supposed to take such a retired climatologist as a serious authority on climate?

    What perhaps we cannot judge is how much a denier knows he is misrepresenting the data he presents, that he is effectively lying. I suppose gross exageration can be justified because the denialist message is to them the correct message and, and denialists don't have the resources to counter all the lies that you climate alarmists generate with all your fake IPCC science.

  22. "Thank you, scaddenp, Daniel Bailey and MA Rodger!"

    For my small contributions, you are most welcome.

    "i have looked at a lot of evidence from both sides of the argument"

    If only there were actual sides.  Because that would imply that both "sides" were roughly equal.

    In the discussions around global warming and its anthropogenic causation, there are those who focus on the science using the scientific method and logic, seeking reproducible evidence that best explains what we can empirically measure.  We call them scientists, the real skeptics.

    Then there is everyone in the extremely small but vocal minority, those who ignore the above in favor of slander, innuendo, unsupported assertion and character assassination in favor of promulgating false equivalence to support the ephemeral facade of "debate" and "sides".

    But it is not about the science, the bulk of the science was settled, decades ago. Deniers posing as skeptics set up a charade tableau of false equivalence to poison the well of public acceptance of that science.

    A parsimonious harping at the font of stolen, out-of-context and context-less emails proven not germane to the science is continuing on in the prosecution of the agenda of denial.

    Truth, science and reputable journalism all sacrificed to the unholy alter of false equivalence under the guise of promulgating a fallacious "debate".

    There is no debate. All that remains is the informed and the uninformed.

    Those professing the false equivalence of "both sides" are the journalist in this story.

    Moral, dear readers:  Don't be that journalist. 

    The discussion surrounding the science of climate change and its human-causation are a Möbius strip comprised of 170 years of evidence from hundreds of thousands of scientists from virtually every country on the planet.  Meaning that from an evidence perspective, only one side exists, because only one side uses evidence.

    Even the petroleum extraction companies researched the subject themselves and affirm the unassailable facts, physics and evidence of AGW.

    Per the oil companies, which admitted it in court, under oath:

    "The issue is not over science. All parties agree that fossil fuels have led to global warming and ocean rise and will continue to do so, and that eventually the navigable waters of the United States will intrude upon Oakland and San Francisco. "

    The People of the State of California vs BP PLC et al (page 6, line 6).

  23. About the "2 sides of athe argument" thing: there is really no such thing when considering all the aspects of climate science studied, the weight of the evidence leaves no doubt. I remember a video clip by James Hansen in which he expressed the problem in the simplest possible visualization: imagine a square meter of the Earth, put a little candle on it, close to one watt of output. Seems like a very little thing. Now put one on every square meter of the planet's surface: every square meter of every ocean, every square meter of the Arctic, Antarctic, every square meter of every city, and of every desert, every square meter of the mountains, plains, every single square meter of the surface of our home planet. This is so staggeringly enormous that it defies the imagination. We humans are not well equipped to think about tis kind of thing and prioritize our other silly preoccupations down.

  24. @ 772 Daniel Bailey

    For my small contributions, you are most welcome.

    Daniel, your contributions have been an enormous help to me...nothing small about them! I am grateful to each person here who responds to the things I post as I've learned so much from all of you!

    @ 771 MA Rodgers

    Well, let that be a lesson for you!!
    Denialism isn't logical. It turns folk into swivel-eyed loons.

    I agree! I've come to realize that there is no point in discussing science with people who are anti-science or not literate in science. It's a huge waste of my time! If they are literate in science but want to learn then that's a different scenario and I feel happy helping them understand scientific concepts.

    However when scientifically liberate people make false statements about science such as the climate deniers do I feel it's a duty to a certain point to expose their misinterpretations or myth spreading lies.

    You guys have helped me to better do that!  

    Thank you!

     

  25. Ops I meant when scientifically illiterate people make false staements...

  26. A question from a denier.

     

    The Northern Part of the US was covered in Ice 20,000 years ago and the Great lakes were only formed 10-14,000 years ago.

    Alaskan Glaciers started receding big time around 1750 to 1900.

    What caused all of that and why is now any different ?

    All insights are welcome. :)

  27. TVC15 @776,

    The denialist asks about the features of two different times and asks what is different today.

    20,000 years ago was the maximum glaciation of the last ice age, this the result of reduced solar radiation for the high-latitude Northern summers which 100,000 years ago triggered an increase in the amount of ice-covered land/ocean in high Northern latitudes. The level of ice was amplified by the increased albedo of the ice reflecting away greater levels of solar radiation and by the reduced GHGs (CO2 & methane) caused by the cooling global climate having a net draw-down of such gases. Thus we find the Laurentide & Cordilleran ice sheets covering mainly Canada and beyond, extending to cover the sites of today's Great Lakes. (The map below ignores changing coast lines.) It thus requires the Laurentide Ice Sheet to melt considerably before the Great Lakes can exist, their formation reportedly beginning 14,000 years ago.

    Ice age N America

    We now leap forward to a time when the Cordilleran ice sheet has long gone. Over recent times the dynamics of glaciers is not always determined by local temperature. A sea-terminating glacier will likely spend most of its days slowing advancing and then, becoming unstable, undergo a short period of rapid retreat. And reduced/increased snowfall can cause a glacier to shrink/expand.

    So is there evidence that "Alaskan Glaciers started receding big time around 1750 to 1900"? Solomina et al (2016) who, in an analysis of global glaciers over the last two millenia, examine land-terminated glaciers in Alaska and see no sign of it. Their Fig 2 shows a GEI index indicating a fluctuation in local glacier size which peaked at about 1880AD. This would explain a "receding big time around ... 1900" but not the earlier 1750 date. Other research may give differing timings but it seems unlikely that there is any proper support for a 1750 to 1900 date. Can the denialist provide support for this bold assertion of his?

    And "why is now any different"? The unprecidented global rise in temperatures will impact glaciers globally, including Alaska.

    Response:

    [DB] Fixed image display issue

  28. "Alaskan Glaciers started receding big time around 1750 to 1900"

    As opposed to those promoting misinformation, looking at the full context of the Holocene, Alaska glaciers have only been recently declining, reversing a 8,000 year period of growth and expansion:

    Per McKay et al 2018 - The Onset and Rate of Holocene Neoglacial Cooling in the Arctic

    "Arctic summer temperatures have decreased for the past 8,000 years, before rapidly warming over the past century. As temperatures cooled, glaciers that had melted began to regrow throughout the Arctic, a phenomenon and a time interval known as Neoglaciation.

    This study seeks to understand the nature of this cooling and whether or not this indicates a tipping point in the climate system. Specifically, we use a large database of records from ice cores, lakes, ocean sediment, and more paleoclimate archives to detect patterns of cooling. We investigate these patterns, and climate model simulations, to determine what parts of the Arctic experienced Neoglaciation at the same time, how rapidly it cooled, and what climate models indicate about the causes of cooling.

    We find that the Arctic did not cool simultaneously, but different regions cooled at different times and that the climate models perform well when simulating both the timing and amount of Arctic cooling."

    Full copy available here.

     

    Further, recent climate warming in the central Yukon region has surpassed the warmest temperatures experienced in the previous 13,600 years (and therefore likely the past 100,000 years).

    Porter et al 2019 - Recent summer warming in northwestern Canada exceeds the Holocene thermal maximum

    Yukon temps

    News release here.

  29. "the Great lakes were only formed 10-14,000 years ago"

    In the spirit of transparency and full context, the basins of the Great Lakes are the product of repeated and successive glaciations, and not just the most recent.  From Larson and Schaetzl, 2001:

    "The basins that contain the Great Lakes are the product of repeated scour and erosion of relatively weak bedrock by continental glaciers that advanced into the Great Lakes watershed beginning perhaps as early as 2.4 Ma. Most of the scouring, however, probably occurred after about 0.78 Ma when episodic glaciation of North America was much more extensive, with ice cover sometimes extending as far south as Kentucky."

    A full perusal of this fine document reveals that the southern lobes of the Great Lakes were ice-free at the near peak of the Last Glacial Maximum at 25,000 years BP and that the most southern advance of the ice during the last glacial phase occurred well after the LGM and during the deglaciation phase of the Laurentide Ice Sheet, when cold (dry) ice processes had shifted over to wet processes (promoting ice flow).  From Figure 8:

    Great Lakes Ice Cover

    Full copy available here.

    The point is, it's pretty easy to show the interested onlooker just how uneducated your particular pretend-skeptic actually is by doing some digging.  The plus side to all that digging is in the self-learning you accomplish.

  30. Thank you both so very much!

    I shared the information that you both offered and a snarky denier came back as spouted off this at me.

    Nothing is unprecedented. Try science.The science is settled:

    Palaeo data suggest that Greenland must have been largely ice free during Marine Isotope Stage 11 (MIS-11). The globally averaged MIS-11 sea level is estimated to have reached between 6–13 m above that of today.

    [emphasis mine]

    https://www.nature.com/articles/ncomms16008

    “Even though the warm Eemian period was a period when the oceans were four to eight meters higher than today, the ice sheet in northwest Greenland was only a few hundred meters lower than the current level, which indicates that the contribution from the Greenland ice sheet was less than half the total sea-level rise during that period,” says Dorthe Dahl-Jensen, Professor at the Niels Bohr Institute, University of Copenhagen, and leader of the NEEM-project.

    [emphasis mine]

    https://www.nbi.ku.dk/english/news/n...e-of-the-past/

    The sea levels are going to rise and you can't stop it, so stop pretending you can.

    What the heck can I make of this denier's snarky reponse?

  31. What the heck indeed. That they confuse MIS-11 with the Emenian maybe? That they think causes of sealevel rise and ice melt in past are the same as the forcing at work today?

    Or more likely: their beliefs are not based on any rational analysis and that they are making 2+2=5 with motivated reasoning.

  32. @ 781 scaddenp,

    Yes indeed what the heck! This denier portrays himself as being scintifically literate but he does not have me fooled. He's pompous and always results to insulting anyone's intelligence if they challenge the rubbish he put out.

    That's a great angel you provide in asking does he think the causes of SL rise and ice melt from the past are the result of the forcing's at work today.

  33. I meant angle!  

  34. TVC15 @780,

    Sea level during previous intergalacials has been the subject denialist blather preented on this thread before. This version is a little different from that @715 & @780 which asserted that all eight previous interglacials saw sea level metres above today's level. Of course there are only two previous interglacials that saw such sea levels - the Eemian (MIS-5e) and 400,000y bp the MIS-11.

    The Eemian was significantly warmer than today in northern latitudes. The link @780 states the temperature became +8ºC warmer than today in northern Greenland. So if temperatures do rise like that, we should expect significant SLR. The denialist appears to be saying that such temperatures are going to arise naturally. Of course, all interglacials are different. That is why only two of the last eight had sea level higher than today.

    MIS-11 is interesting because it was of longer duration than other interglacials. This resulted from the milankovitch cycle that triggered the interglacial being followed 20,000 years later by a stronger peak in the cycling extending the interglacial accordingly. A comparison of MIS-11 & the present Holocene is provided by Rohling et al (2010). The milankovitch cycles do not provide that extra boost for the Holocene so again there is no reason to have expected 20,000 more years of interglacial with sea level increasing above today's levels - not without AGW.

  35. MA Rodger @780 

    Thank you so much. I learn so much from you all when I post the denialist blather that deniers challenge me with.

    Thanks for the link to the Rohling paper.

  36. I have to agree with TVC.  The exchanges between the experts and the well informed and the deniers has given me a more detailed look at the different aspects of AGW.  

    I've been here lurkinga couple times a day since the inception of this blog site.  I read most of the articles and love going to the commets where things get fleshed out. 

      

  37. MA Rodger @ 780

    Where can I find easy to understand data that shows that only two of the last 8 eight had sea level rise higher than today?

    Also a denier is trying to say that  Milankovitch Cycles are irrelevant.  Where do they get idea that from I wonder?

  38. TVC15 @787,

    800,000 RSL

    This graphic has already appeared up-thread and is snatched from the web but originates from this webpage. (You need to click the top-left icon to get the 800,000 year version.) The underlying study is Spratt & Lisiecki (2015).

    If your denier who is "trying to say that Milankovitch Cycles are irrelevant" actually manages to achieve such an assertion, perhaps he should be asked what would trigger ice ages if not milankovitch cycles?

  39. MA Rodger @ 788

    Thank you so much!!!!!

  40. Bølling-Allerød seems to be a period when rapid warming far beyound today's was powered by  heat from warm waters originating from the deep North Atlantic Ocean.  It seems to have nothing to do with CO2.  This was pointed out to me by a skeptic after I claimed that present day warming is unprecented.  Reading up I discovered that from what researchers could determine the temperature rose more than a degree in less than a year and 3 to 4 degrees Celcius over a short period of time.  Needless to say I was surprised by this as well as finding nothing in the Skeptical Science search.

    Can you recommend an article on the subject.

  41. Estoma @790 , 

    I am not sure whether you are comparing arctic-localized (e.g. Greenland ice-core temperature proxies) changes with worldwide changes of smaller degree.

    There were also steep rises in Greenhouse gasses (especially methane) and giant meltwater pulses affecting sea-level & the oceanic heat transfer from the tropics.  All producing rapid fluctuation (see the Younger Dryas ).  Still, one needs to ask: what caused the melting of land ice-sheets  ~ if it wasn't caused by cumulative effect of gradually increasing Greenhouse effect?  (That is a question that the "skeptics" don't wish to ask.)

    The present-day rapid worldwide warming is not part of a transient up-and-down fluctuation, but is a strong & steady rise with a clear ongoing causation by CO2.  World temperature has (compared with the gentle & slight variations of the past 10,000 years of the Holocene) now abruptly risen higher than the Holocene Maximum and is still rising steeply.  And has occurred at a time (of roughly 5,000 years' duration) where the natural background tendency is toward ongoing global cooling.

    Altogether, the two cases (of B-A events versus nowadays) are so very different in their long-term importance, that it is perfectly fair to say that current-day gobal warming is unprecedented in its character ( and in its human causation !! )

    I think your "skeptic" is indulging in some Motivated Reasoning, and playing with words, in order to conceal the plain physical truth of what is happening globally.

  42. I figured the genisus was "from the strong & steady rise with a clear ongoing causation by CO2."  What flumoxed me was that the warming had occured at light speed; world wide from what I read.  I didn't realize that had been any  case like this during this inter glacial period. I'll have to add a cavet from now on when I make the unprecedented warming statement.

    It appears that today's temperature is still higher than it was 13,000 years ago but I was unable to find temperature  graph for the world outside of the Arctic that went beyound 2000.

  43. "I was unable to find temperature graph for the world outside of the Arctic that went beyound 2000"

    That can seemingly be an obstacle, but global reconstructions are becoming more common, depending upon the time period you're interested in.  For example, these are useful summaries (sources used listed on each):

    The last 10,000 years

    10,000 years

     

    The last 20,000 years

    20,000 years

     

    The last 800,000 years

    800,000 years

     

    As always, clicking on the images should make them bigger. 

    Images from Bruce Railsback's Fundamentals of Quaternary Science.

  44. Thank you Danial for the graphs.  You come up with lots of good stuff.

  45. Here's some more climate change denier blather I came across today.

    When you are using a complicated explanation to detail why something is happening, or is believed to be happening, you have almost certainly overlooked a much simpler reason for it.

    In the case of CO2, we already know from the fossil record that levels have been much higher in the past and also lower.

    During periods of low atmospheric CO2 levels, surface temperatures have been significantly higher.

    Likewise, during periods of very high CO2, temperatures were cooler than we are experiencing today.

    In fact, the only consistent relationship between CO2 and surface temperature seems to be the slight increase that follows a warming period as the oceans release stored CO2.

    So, when doubling the atmospheric CO2 level results in a claimed surface temperature change that is essentially imperceptible to the senses, the question becomes, how do we know the temperature has actually increased.

    Assuming an increase in surface temperature can be verified (good luck with that), the next question is, is it really caused by elevated CO2 levels and to what degree?

    What other factors are in play and, most importantly, what other factors cannot be measured and their influence accounted for?

    On the issue of cloud cover, NASA essentially punts.

    They admit that past cloud cover was never measured in any meaningful way and that measuring cloud cover, even with the technology available today, is more or less a scientific fool's errant.

    Of course, the problem is that we can't account for the effect of CO2 unless we also account for the effect of cloud cover, then and now.

    I could go into refrigerants in the stratosphere, the albedo effect, rain and humidity and other factors that are clearly ignored by the settled science crowd, but why bother.

    CAGW is a religion dressed up as a pseudo science trying to pass itself off as legitimate science.

    The reason questions that ought to be asked are not asked is because we would have to admit that the data is insufficient, unavailable and probably unknowable.

    There are so much illogical claims here I don't know where to start!

  46. TVC15 @795 ,

    I am assuming that you are dealing with a single denialist who tries to bury you under a blathering gush of Gish Gallop.

    IMO, best to challenge him on just a few points of his gush :-

    (A)  Planetary surface temperatures show a good correlation with the *combined* effects of changes in solar output and variations in atmospheric CO2 level.  Examples: look at the cooler/warmer periods of the Ordovician Age and also the Carboniferous Age, as well as the Cenozoic recently.  Sometimes the CO2 rise was caused by the temperature rise, and sometimes (such as the last 150 years) the CO2 rise preceded & caused the temperature rise.

    [to him] "Question: Why are you apparently unaware of all that paleo evidence?"

     

    (B)  We know the surface temperature is rising, because [i] satellite evidence shows land and sea ice is melting, and [ii] satellite and tide-gauge evidence shows rising sea level, and [iii] thermometers confirm the rising temperature (a rise now of almost 1 degree since reliable general measurements commenced).

    [to him] 'If you cannot understand such basic science, then your "can't feel it" opinion is worth nothing.'

     

    (C)  The scientists have looked into all sorts of factors that might influence climate (ranging from clouds and cosmic rays, to greenhouse gasses and albedo changes).

    [to him] "If you yourself have discovered a vitally important factor they overlooked, then [i] tell us what it is, and [ii] write to the National Academy of Sciences, and explain to them what morons they all have been for missing such a basic factor, and (iii) start planning how to spend all the Nobel Prize money that you will be awarded from the astounded and delighted Nobel Committee !   .....And good luck with that, Mr Unappreciated Genius."

    (Doubtless he will start shifting goalposts, and/or go into strawman arguments, and/or go into Conspiracy Mode.)

    .

  47. TVC15 @795,

    Your denialist runs through quite a complex argument, so probably well rehearsed but it is not very concerned with reality.

    The talk of the decoupling of global temperature & CO2 is probably going back hundreds of millions of years. There is an SkS post on this here (& probably other too) but I would punt the ball back into the denialist's court and ask which era they are talking about. They probably have some ancient denialist graph showing CO2 & temperature less than strongly coupled but addressing specific eras is the way forward, not trying to debunk some bogus lines on a graph scribbled out years ago, (usually with temperature a parody of this Scotese graph).

    The denialist presumably dismisses the tight coupling of CO2 through the last million years of ice ages with their "slight increase that follows a warming period". Then they plunge into the bold assertion that denies temperatures have been increasing over recent decades. If they require it to be "verified" they obviously haven't understood how thermometers work, how calendars work (winters and shorter, summers longer under AGW) and a whole ot more. This is village idiot talk.

    Their final run is in arguing for there being other causes for the temperature increase which is exceptional over thousands of years but that they deny exists. It would probably be better responding that the cause of such an exceptional global temperature change requires a cause, not just a list of mechanisms that impact the climate system. So if they want to invoke rain or humidity or clouds, what has set these off to cause this exceptional warming now?

    One of those they point to as a potential cause is, of course, manmade. CFCs & HCFCs would have been as bad as CO2 at forcing AGW if they hadn't been banned. There is also albedo which could be forced by land-use change as well as cloud (& there are denialists that have argued this as the cause of warming, although measured albedo shows nothing to support such an assertion).

    Their final talk of "questions that ought to be asked" could be another approach to a reply - what questions? Be specific!!

  48. Eclectic @796

    MA Rodger @ 797

    Thank you both so much! I learn so much everytime I come here and post the weird things that denialists state.

    Thank you both so much!

  49. MA Rodger @788

    OK so I shared the link showing that only two of the last 8 eight had sea level rise higher than today and this is what he came back with.

    No, it's every single one of them.

    Here's more science showing sea levels in MIS-7 and MIS 9:

    The presence of a sea-level highstand at E180 ka represents a challenge to the idea that Pleistocene climate is driven by summer insolation at 651N. Sea-level is increasing (and therefore ice is melting) when 651N summer insolation is at one of its lowest points of the last 400 ka.

    [emphasis his the denier]

    Recognition of non-Milankovitch sea-level highstands at 185 and 343 thousand years ago from U–Th dating of Bahamas sediment

    https://www.whoi.edu/cms/files/Hende...2006_21693.pdf

    Here's another on MIS-7...from your own government....omigod...how can you debunk your own government?

    Thermoluminescence (TL) and electron spin resonance (ESR) ages from sediments and fossil shells point to an age of ?220 ka for the end of this marine transgression, thus correlating it to MIS 7 (substage 7e). Altimetric data point to a maximum amplitude of about 10 meters above present-day mean sea-level, but tectonic processes may be involved.

    https://www.ncbi.nlm.nih.gov/pubmed/25590701

    Sucks to be you.....you can't scream, "Oil company funded research!"

    The last interglacial (LIG; also known as the Eemian or MIS5e) lasted from 129 to 116 thousand years before present (ka).

    If we look at EPICA Ice Core Data for CO2 levels in ppm, we find:

    YBP ..... ppm CO2

    116,501.... 262.5
    117,750.... 267.6
    118,649.... 273.7
    119,672.....271.9
    120,382.... 265.2
    121,017.... 277.6
    122,344.... 272.1
    123,070.... 276.4
    124,213.... 268.7
    124,257.....266.6
    124,789.... 266.3
    125,081.... 279.7
    125,262.... 273.0
    125,434.....277.1
    126,347.....273.7
    126,598.....267.1
    126,886.... 262.5
    127,132.....262.6
    127,622.... 275.3
    127,907.... 275.6
    128,344.... 274.0
    128,372.....287.1
    128,609.....286.8
    128,866.....282.6
    129,146.....264.1
    129,340.....263.4
    129,652.... 257.9
    129,736.....259.0

    For a brief period, CO2 levels were in the 280s ppm CO2, but for the most part below that and the average is only 271.7 ppm CO2.

    That, is Science, and Science says sea levels are going to rise and you can't stop it.

    I've never stated that sea levels are not going to rise so him tossing that in at the end is a non sequitur.

    I don't think that either link he posted is refering to sea-levels being higher than the two interglacials you mentioned in 784. (only two previous interglacials that saw such sea levels - the Eemian (MIS-5e) and 400,000y bp the MIS-11).


  50. TVC15 @799,

    It is a rather incoherent rant from your denialist. When you raise the point that only two of the last 8 interglacials were higher than today, he responds "No, it's every single one of them." Yet nothing he presents (his "science") is saying that all past interglacials had sea level above today. Indeed none are saying that global sea level was any different to your assertion (2 of 8 higher).

    He presents two references.
    Henderson et al (2006) is discussing the timing of the interglacial high stand in the Bahamas during MIS7 & MIS9 (note MIS9 is also one of the 2 past interglacials that were higher than today). They were certainly not considering the height of the peak sea level globally. Even if Henderson et al were discussing the height of the highstand, the isostatic movement of land means a local measure of relative sea level is not a reliable marker of global sea level. Nowhere do Henderson et al mention isostatic land movement. The height of the highstand is not their thesis, the timing is. (Note in the following reference Lopes et al, fig 6 shows the MIS1 holocene highstand 4 metres above present sea level. This would be down to local isostatic movement.)

    The denialist's second serving of "science" is Lopes et al (2014) is again primerally concerned with dating and having concluded that it is an MIS7 highstand they have identified, do not proclaim that MIS7 sea level has been underestimated (as the denialist concludes). Instead they look to find reason for their highstand being higher than they would have expected, their suggestion being that plate tectonics may be at work.

    The denialist then sets out non-controversial CO2 levels from the Eemian. Quite how this links to his final grand "science says" assertion can only be speculated. Is he saying that if CO2 was below 300ppm in the Eemian with its higher sea level, then (sarcastically perhaps) with CO2 at 400ppm today sea level must rise?  Strangely, this is the case. The warming resulting from increased CO2 will add perhaps 2.3m/degree C to global sea level, according to IPCC AR5.

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