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Climate Hustle

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

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Comments 701 to 710 out of 710:

  1. @ 699 MA Rodger,

    What is a discal projection?

  2. Hi MA Rodgers,

    Why would the denialist consider that just 5% of atmospheric CO2 is down to anthropogenic causes? That would be just 20ppm. Where did the other 110ppm come from? That's 860Gt of CO2 so the source should be quite evident.

    I'm a bit confused. What do you mean by where did the other 110ppm come from?

  3. TVC15 @700. Re. CO2 levels in the distant past, see this rebuttal: Do high levels of CO2 in the past contradict the warming effect of CO2?

  4. I need your help again guys!  I posted this statement: In July 2007, a survey of hurricanes in the North Atlantic over the past century noted an increase in the number of observed...

    A denier who many on the sidelines thinks is brilliant and who I suspect is being paid to spout what he spouts responded with this.

    "The operand is "observed."

    You have the technology to observe both tornadoes and hurricanes that you were never able to observe in the past.

    And that's the recent past, outside of the last 50 years.

    There's no science behind "climate change." It's all political and socio-economic-based:

    German economist and Intergovernmental Panel on Climate Change (IPCC) official Ottmar Eddenhofer, explained prior to the Cancun conference in an interview with the Global Warming Policy Foundation (Potter 2010): First of all, developed countries have basically expropriated the atmosphere of the world community. But one must say clearly that we redistribute de facto the world's wealth by climate policy. Obviously, the owners of coal and oil will not be enthusiastic about this. One has to free oneself from the illusion that international climate policy is environmental policy. This has almost nothing to do with environmental policy anymore, with problems such as deforestation or the ozone hole...Basically it's a big mistake to discuss climate policy separately from the major themes of globalization.

    In a paper prepared for the Cancun conference Professor Kevin Anderson, Director of the Tyndall Centre for Climate Change Research, said the only way to reduce global emissions enough, while allowing the poor nations to continue to grow, is to halt economic growth in the rich world over the next twenty years.He called for World War II-type rationing of electricity in order to force people to conserve (Gray 2010)

    Source: http://www.usu.edu/ipe/wp-content/up...Climate-Policy"

     

  5. @703 David Kirtley thank you so much. Odd that did not come up when I searched for Ordovician-Silurian.

  6. This is more motivated reasoning. Well obviously there is science behind it - the whole IPCC WG1 is nothing but science. However, solving it is political and economic and the argument he is trying is that there is a nefarious plot by scientists who want everyone including themselves to suffer massive economic damage for no good reason except... But people which view the world through ideological glasses seem to believe this.

    There is also the IPCC WG3 on ... solutions. In there you can see the published opinion from the many that have studied the issue instead of the opinions (misrepresented at that) of carefully chosen few.  I wonder how well Ottmar Eddenhofer feels his views were represented by the Global Warming Policy Foundation.

  7. I would also say this is totally off-topic. PLease put your comments in an appropriate thread.

  8. TVC15 @701,

    The sun illuminated the disc of the Earth with an intensity measured by TSI. The disc has an area of πr^2. But this energy is spread out, not over a disc but over a globe with area 4πr^2. So TSI requires dividing by 4 to give the average solar climatic impact.

    TVC15 @702,

    The denialist is quoted @695 saying "Is man made CO2 not 5% of atmospheric CO2?" With 410ppm CO2 in the atmosphere, 5% would be 20ppm. But since pre-industrial times CO2 has rise from 280ppm, a rise of 130ppm. If mankind is responsible for only 20ppm of this, where did the other 110ppm come from? Perhaps the denialist is believing that this extra 110ppm is down to the shape-shifting lizards, or perhaps all the unicorns he sees inhabiting the world.

  9. MA Rodger @708

    Thank you for the clarifications! 

    scaddenp @ 706,707

    Ops sorry to step off topic but I appreciate the insights. I read some interesting information about Eddenhofer on Desmog.

  10. Hi Again,

    I'm not sure how to respond to these types of denalist claims.

    So how does one parse out the individual influences of the sun, CO2, water, and now "sulphate aerosols"?

  11. The assertion of the author can be countered with many examples. The subject of longterm climate patterns is so complex and beyond current human understanding that any assertions are highly suspect.

    Response:

    [PS] Argument from personal incredularity. I suggest you take time to inform yourself of the science and respond with research to back your assertion.

  12. Warend @711 ,

    over less than one hour, you have made 4 comments in 4 separate threads here at SkS.   Each comment was distinctly fatuous.   So the readers can only draw the conclusion you are not a bot.    ;-)

    Warend, you are posting on the wrong website.   This website here is for rational skeptics.   Your comments would have a much better fit at WhatsUpWithThat ~ a website where misery loves company.    ;-)   

  13. All these arguments are irrelevant as mankind is destroying the wildlife and environments of earth.

    Unless mankind changes immediately Man will be extinct before 2400

    The earth does not need mankind!

    Stop polluting the land and seas, stop cutting down the trees, and stop and feed the poor!

    Educate the population so that the population falls. 

    You don't have a choice!

    PB

  14. "Unless mankind changes immediately Man will be extinct before 2400"

    Probably earlier?

    “The IPCC report that the Paris agreement based its projections on considered over 1,000 possible scenarios. Of those, only 116 (about 10%) limited warming below 2C. Of those, only 6 kept global warming below 2C without using negative emissions. So roughly 1% of the IPCC’s projected scenarios kept warming below 2C without using negative emissions technology like BECCS. And Kevin Anderson, former head of the Tyndall Centre for Climate Change Research, has pointed out that those 6 lone scenarios showed global carbon emissions peaking in 2010. Which obviously hasn’t happened.
    So from the IPCC’s own report in 2014, we basically have a 1% chance of staying below 2C global warming if we now invent time travel and go back to 2010 to peak our global emissions. And again, you have to stop all growth and go into decline to do that. And long term feedbacks the IPCC largely blows off were ongoing back then too.”
    https://www.facebook.com/wxclimonews/posts/455366638536345

    “ The level of fossil fuel consumption globally is now roughly five times higher than in the 1950s, and one-and-half times higher than in the 1980s, when the science of global warming was confirmed and governments accepted the need to act on it. This is a central feature of the “great acceleration” of human impacts on the natural world. . . .
    CO2 emissions are 55% higher today than in 1990. Despite 20 international conferences on fossil fuel use reduction and an international treaty that entered into force in 1994, man made greenhouse gases have risen inexorably.”

    piraniarchive.files.wordpress.com/2018/08/pirani-helsinki-wern2018-paper.pdf

  15. I've come across another climate change denier who stated these things.

    If you read the peer-reviewed scientific articles, you will see that in every Inter-Glacial Period going back 800,000 years the sea level rose 3 meters to as much as 14 meters.

    Sea levels during MIS-7 and MIS-9 were 10 meters to 14 meters higher than present.

    What did you just say?

    You said CO2 levels haven't exceed 300 ppm CO2 in 1 Million years.

    So, what exactly is the point?

    Who was burning fossil fuels in any of the previous Inter-Glacial Periods?

    No one, yet sea levels still rose 3 meters to 14 meters.

    In fact, CO2 levels ranged from 260 ppm to 280 ppm CO2.

    So, the reality is that it doesn't matter if your CO2 level is 270 ppm or 470 ppm, because your sea level is going to increase 3 meters to 14 meters and neither you, nor anyone living, dead or who will ever live can stop it.

    Once you accept that scientific reality, the best thing to do is let the Free Market handle it, instead of ramming useless laws down people's throats that will do nothing except screw people over.


    I this he's cherry picking and misrepresenting.  

    My questions are:

    1. Is it an accurate claim that in every Inter-Glacial Period going back 800,000 years the sea level rose 3 meters to as much as 14 meters?
    2. Is it accurate to state that it doesn't matter if your CO2 level is 270 ppm or 470 ppm, because your sea level is going to increase 3 meters to 14 meters and neither you, nor anyone living, dead or who will ever live can stop it?

     

  16. I meant to state that I think he's cherry picking and misrepresenting. 

  17. TVC15 @715,

    The claim that "in every Inter-Glacial Period going back 800,000 years the sea level rose 3 meters to as much as 14 meters" is garbled nonsense, as is the comment about MIS-7 & MIS-9. The 'rise' presumably refers to SLR exceeding today's levels and the "3 meters" is probably referring to MIS-5 (although it is usually given as a little higher) which was the last interglacial 100,000 years ago while the "14 meters" is probably referring to MIS-11 400,000 years ago. (MIS-7 & MIS-9 were the interglacials inbetween these two.)

    Reconstructing a SLR record over recent ice-ages is not as simple as the equivalent CO2 & polar temperature record. So it is not impossible that wildy contrardictory evidence exists and I'm not aware that a definitive source for ice-age SLR actually exists yet. Our good friend Google provides the graphic below although it requires signing-up to get a proper sight of the data it is based upon.

    SLR over 800,000 years

    As for CO2 being below 300ppm during those previous interglacials, it was the planet's orbital configuration that allowed that extra ice-melt back then, the whole amplified by reduced albedo due to lower ice cover. Today those orbital configurations do not exist so without mankind's GHGs the planet would now be slipping into an ice-age and sea level would have been dropping. Our extra GHGs is more than preventing that and CO2 levels of 470ppm (not sure why that particular value is stated) will melt out Greenland (as happened in MIS-5) and a fair bit of Antarctica as well. So 14m SLR would be on the cards, although the melting is expected to take some millennia if you managed to stop at 470ppm.

  18. MA Rodgers @ 717 

    Thank you once again for educating me so I can educate others!

    With respect to the state of this planet and human activity I now see that's it too late to undo what human activity is doing to our climate.

    I apologize if I come across as a "Debbie downer" but from all that I've learned thus far...it appears that this earth cannot overcome human caused destruction until we destroy ourselves.

    I am not saying we should simply stop trying but when I look around the globe it's pretty evident that what we've unleashed on this earth is not stoppable even if fossil fuel use ceased 100% today.

  19. @TVC15,

    Don't be so sure about that. While humans have huge destructive capacity, we also have tremendous creative capacity too.

    You are right about just dropping emissions to zero won't be enough. That's been in the IPCC models all along. But the carbon cycle is just that...a cycle. There are two sides to balance. While reducing emissions can't work alone, the other side of the carbon cycle is sequestration. And it only takes about a 10% improvement on the natural carbon cycle sequestration side worldwide to offset emissions. 

    So while it is controversial still, we actually do have the capacity to improve the long term sequestration side of the carbon cycle at the same time as we reduce emissions. That means we actually can get to a drawdown scenario and it is not yet too late.

    I wrote this up to show how:

    Can we reverse global warming?

    That gets us back to the IPCC scenario that stabilizes the climate! So no. It is not too late.

    And there are more details regarding the emissions side of a drawdown scenario here:

    Drawdown

     

    And more information on how to properly set up a carbon market to facilitate both emissions and sequestration here:

    Farming a climate solution.

     

    Emissions is straight forward in a fee and dividend system. You put a fee on fossil fuel sources. That makes people search for low carbom alternatives, which are abundantly available already. The fee just makes them relatively cheaper. But then we take the dividend and use it to pay for measured verified carbon sink increases (rising SOC), and the two together can get us to a net negative.

    There are still a few people quibbling over nonsense like which sector should take the heavier load. Should energy take 50% and agriculture the other 50% on the path to a drawdown scenario? Or should it be 80%/20%? Or maybe even 20%/80%? It really doesn't matter as long as in the end we get to a net negative atmospheric carbon flux.

  20. Thank you RedBaron @ 719

    To be honesty I have no faith in the human species. Overpopulation leading to humans crowding out and forcing other animal and plant species into extinction on top of the GHG emissions and all the other human activities that's destroying life on this earth is why I have bleak outlook on the human species. 

    I sometimes wish I did not know of all the mass destruction humans are causing. Climate change is just one in many things humans are contributing to.

    I digress.

  21. Don't digress because one is just a symptom of the other, and fixing one fixes both. And more importantly to your lack of faith, please remember. Science is about evidence not faith.

    Soil Carbon Sequestration Potential for “Grain for Green” Project in Loess Plateau, China

    Sure that paper just discusses potential. But in fact the project did go forward and has indeed suceeded in already restoring ecosystem function to vast acreage and is even now sequestering approximately 25% of China's emissions. The effect is so profound and widespread it can be seen from space.

    Human Activity in China and India Dominates the Greening of Earth, NASA Study Shows

    So you see? Where the highest human population density on the planet is also the most improvement in ecosystem restoration, which is actually already making significant strides in restoring ecosystem function over vast areas...

    Now is not the time to give up with dispare. Now is the time to tighten your belts and get to work! We have a lot of work to do and pouting around with gloom and doom is not helping one bit.

    We can do it. Get er done!

  22. Hi RedBaron @ 721,

    Trust me I am a scientist and I know science is based in evidence not faith.

    In thinking about your first response to me with respect to the quibbling over which sector should take the heavier load...do you really think either one is going to simply agree to taking the heavier load? I don't. These two sectors have tons of money to buy any lobbyist or politician they want in order to fight against taking any load. And I'm certain there will be resistance from both sides.  Thus this leads me back to it's too late to turn back now.

    Just look at the current heat wave hitting India with those crazy high temps!  Even with this news you still see the deniers in the US and around the globe.

    I am not a doom and gloom type gal, just a realist.

  23. @ RedBaron 721

    Those are two truly encouraging links you posted about China and India dominating greening the earth! 

    Thanks for sharing this!

  24. TVC15 @724,

    There were of course "EXTREME" climate processes prior to mankind arriving on the scene. These can perhaps be classified into two different groups.

    The first can include really big changes but they occur very slowly, although sudden on a geological time-scale. So the end of the last ice age saw a rise of perhaps 6ºC in global temperature over 8,000 years or 55 million years ago the PETM which saw similar temperature rises over 40,000 years (long enough for, for instance, horses to adapt to the temperature increases by slowly evolving from pony-size into the size of large dogs).

    The second group are far more sudden, the suddenness often obvious. A big volcanic eruption (Mt Toba 74,000 years ago), a meteor strike, or a sudden influx of fresh water that destabilises ocean currents (as per Dansgaard–Oeschger events). This second group can still have very very big local effects but obvious causes that soon dissipate (althugh D-O events can take 2,000 years to return to the prior climate).

    But in all this, I'm not sure what a denialist is trying to argue. If we wait long enough there will eventually be a mega-volcano blow its top, or a big meteor will eventually strike the Earth. (There isn't enough ice about for a D-O event to occur without an ice-age.) So is the denialist suggesting we set about creating our own climatic disaster to allow us to practise for how to respond to the real thing? Or does he want an explanation for every wobbly bit of paleoclimate before he will accept the blindingly obvious fact that it is humanity driving todays warming climate and it will not end well if we don't do something about it?

  25. I accidently deleted the following comment. My bad.

     

    TVC15 at 19:59 PM on 4 June 2019 

    Is there an easy answser for this question being asked by a climate denier?

    And as you know, nature's impact on climate can and has been EXTREME prior to man, and man's industrialization. How do you account for that?

    So far from what I've learned from you guys is Earth's orbit, solar output, the sun being cooler, greater volcanic activity, rock weathering, surface ice albedo, massive amounts of Dinosaur gas? (sorry guys I had to toss that in for grins)

    Are there other factors I missed?

    Thanks!

  26. Thanks MA Rodger @ 724

    The climage deneir was the one who made this statment: And as you know, nature's impact on climate can and has been EXTREME prior to man, and man's industrialization. How do you account for that?

    In my orgional post I had it indented so others would know this was not my statment.

  27. Thanks again MA Rodger @ 724

    The deniers worship the US climate denier blog sites such as WUWT. It's ridiculous what that site puts out. The US also has the Heartland Institute whose mission is to instill doubt in American minds about the science of climate change than the Heartland Institute.

    This is a tyical US denier rant:

    "Hot places get hotter in the summer. Weather is not climate, but climate changes naturally due to the Sun, and other factors. If you want to live like a Stone Age Stooge, plus pay exorbitant prices for energy and ALL products and services, be my guest, but don't force others to follow your cult like religion to make yourself feel relevant in the Universe."

  28. Hi again,

    I'm not sure where to post this but I think this might be the correct thread since it deals with past changing climate.

    I'm dealing with deniers who are questioning what caused the end of the last ice age and the melting of the Laurentide ice sheet?

    I came across this 2015 article with respect to the Laurentide ice sheet and wanted to know if there are other studies you can point me to.

    However with respect to the Younger Dryas I came across this: The Younger Dryas.

    For some reason the deniers seem to think these two events somehow "prove" that human caused global warming is a hoax generated to "take our money". 

    However these two events are not relevent to our current climate situation because we are not at the end of a glacial period.  

  29. TVC15 @728,
    This is probably not the answer you were expecting.
    You're asking about three seperate things, two of which are far from straightforward - ☻ The trigger that ended the last ice age, ☻ The melting of the Laurentide ice sheet and ☻ The Younger Dryas episode - and these  linked to some denialist argument which is not so evident.
    Thinking about the linkage to denialist argument:-
    Is it that it shows climate can change rapidly without humans emitting CO2 (but which does require millions of cubic kilometres of strategically-placed ice that would be difficult to miss)? Is it that we do not know exactly what happened 20k & 13k ago so how can we be sure about today (when we do see exactly what is happening today, or exactly-enough)?
    I have to say I cannot see how any denialist argument would begin to stand up.

    So what triggers a de-glaciation. Milancovitch cycles of course. But can you see these triggers. (Image from here.)
    Milankovitch cycle graph
    The triggers aren't so obvious as the ice-age needs to be primed as well as triggered. Ice-ages used to occur every 40ky but over the last 1,000ky they last 100ky. (I think there's been some progress towards answering why - possibly more exposed bedrock.)
    And within ice-ages there are other events that still come with significant questions - Dansgaard–Oeschger events, Heinrich events and the Bølling-Allerød warming that immediately preceeded the Younger Dryas.

    While you asked for some reading, let's start with a 32-second video, the melt-out of the Laurentide ice-sheet.
    Note in the video the big lakes that build in the millennia before 13kybp. The initial take on the Younger Dryas was that it was the sudden draining of these lakes that caused the AMOC to collapse & precipitate the Yonger Dryas. But evidence for such an outflow remains elusive (the Wikithing references to a Mackenzie River outflow are Murton et al 2010 & Keigwin et al 2018), but some research suggests it has to be more complex than that.

    And in all that, there is the wonderous Impact Hypothesis (& apparently others according to Wikithing Younger Dryas page). So it all gets a bit heated at times, but probably not enough to melt out an ice sheet.

  30. Hi MA Rodger @ 729

    I truly appreciate that response! I'm learning so much from your responses!

    However I don't know what you mean by this: 

    (but which does require millions of cubic kilometres of strategically-placed ice that would be difficult to miss)?

    Thank you!

  31. TVC15 @730 , he was referring to the vast amount of ice in the Laurentide ice sheet and the subsequent formation & draining of Lake Agassiz (the outflow of cold water, thought to be the main triggering of the Younger Dryas event ~ i.e. that brief hiccup during the initial warming-up phase of the Holocene).

  32. TVC15 @730,

    I wrote @729 "climate can change rapidly without humans emitting CO2" but added that this "does require millions of cubic kilometres of strategically-placed ice that would be difficult to miss". I was thinking a little more broadly than suggested by Eclectic @731. In very simple terms, rapid bits of climate change results from obvious causes.

    A big volcano (like Mt Toba c73ky bp) or an asteroid strike fall into that category but the climate quickly reverts back afterwards. Big ice sheets can cause rapid change which lasts far longer. I had in mind two different ice-induced phenomenon, a big one and a rapid one although properly I was only thinking of the "rapid" one.

    By the "big" one, I mean the ice-age cycle itself which swings global average temperatures by perhaps 6ºC but takes millennia to achieve this (not very rapid) as it requires the melting of millions of cubic kilometres of ice (43 million in the last deglaciation). The major factor in the swing is the change in albedo due to the growing/shrinking ice sheets. CO2 as a factor is smaller, and the result of what Ganopolski1 & Brovki (2017) [PDF] call a complex "stew" of many mechanisms which don't all work to increase the ice-age effect.
    So for ice-age cycles to happen, we do require tens-of-milions of cu kms of ice to melt/freeze on top of the correct bits of land.

    Significant & "rapid" climate change (at least on a regional scale) can be seen in the Younger Dryas and in Dansgaard–Oeschger events. While there is some remaining cotroversy with the Younger Dryas (so let's not go there), it appears reasonably uncontested that the Dansgaard–Oeschger events result from the AMOC suddenly switching back on having been previously slowly strangled by big unstable ice sheets melting/discharging icebergs. The AMOC-forced-by  the ice melt/discharge switching on & off messes up regional climate and produce the big and rapid changes in regional temperature, Greenland ice cores recording a number of regional swings of +5°C in less than half a century. (Note that wIth polar amplification, you'd expect "humans emitting CO2" under BAU to manage a similar-sized swing.) But when the ice-age melts away & "without humans emitting CO2", there is little ice to mess with the AMOC during the less-dramatic Bond events which have little impact on even local temperature.

  33. it should also be noted that D-O and Bond type events are observed when emerging from an ice-age, not during interglacials.

  34. Much appreciated MA Rodger, Electric and Scaddenp!

     

  35. Can you guys help me to understand how to respond to these types of claims?

     

    CO2 levels were 24,000 ppm CO2 for nearly 3 Billion years and there was no runaway greenhouse effect.

    CO2 levels were 8,000 ppm CO2 for several Million years and there was no runaway greenhouse effect.

    CO2 levels were 2,000 ppm CO2 for several Million years and there was no runaway greenhouse effect.

    So, why would 1,200 ppm CO2 over a few centuries cause a runaway greenhouse effect?

    It wouldn't. It's just fear-mongering alarmism by a man who makes his money proffering this nonsense.

     

    Thanks!

    Response:

    [PS] Just a little bit effort with the search button would find the answers to most of these as would a read of the IPCC WG1.

  36. TVC @735 , there's no scientific study [to my knowledge] supporting "Runaway" greenhouse effect being possible on Earth.   I think those friends of yours are suffering from a fantasy life of runaway strawman arguments.

    Perhap they misunderstood something they heard somewhere. 

  37. TVC15 @735,

    I think I would respond to such a silly comment by asking for the name of this man they are talking about, this because such knowledge may assist in sorting out why they are asking such silly questions.

    But a more direct approach, but more involved could be:-

    There is perhaps a philisophical aspect to the "runaway greenhouse effect." CO2 emissions/CO2 levels that are directly due to man's actions will result in an elevated global temperature and this will result in a further CO2 emissions that are NOT directly due to mankind, this extra CO2 resulting in yet further warming.

    So when would that "further warming" be considered as "runaway"?

    If human emissions totalled 4,000 Gt(C) before we stopped, which is eight-times what we've done so far, that would increase global temperature by perhaps +6ºC which would cause natural emissions of let's say another 4,000Gt(C). These "feedback" natural emissions from a 1,200ppm CO2 world would cause further warming, resulting a total of say +9ºC in a 2,400ppm CO2 world. And then the warming would stop. So is +6ºC with +3ºC of that feedback, is that "runaway"?

    Consider if the physics were such that it didn't stop there, that creating CO2 levels of 1,200ppm would result in say 40,000Gt(C) extra CO2 in the atmosphere - roughly 20,000ppm - which is all the carbon in the oceans & soils (but the rocks would still contain the bulk of the planet's carbon), the temperature would ratchet up to who-knows what temperature and all would see this as runaway warming.

    But at some level it would stop. Any runaway system will eventually stop. Always it will stop somewhere.

    The important thing is whether the runaway effect is so significant that it presents a "wheels-fallen-off" situation. Back in the days of the Hadean or Archean, there may well have been far more than 24,000ppm CO2. Such levels are argued because of the faint young sun paradox. But the Hadean earth was not back-then a "wheels-fallen-off" situation because there was no humans requiring a climate compatable with their needs, while a return to the Hadean climate today would obviously be a "wheels-fallen-off" situation.

    But the physics isn't like that. While a directly-human-caused 1,200ppm CO2 world would result in an additional CO2 boost from warmer oceans & Arctic, any resulting additional temperature rise will be limited so a result like Venus or the Hadean is an impossibility. But that additional CO2 boost will be big enough to make what is an already-very-very-difficult situation for humanity very-very much worse. I would suggest that the increase in suffering from that additional CO2 boost would be enough for some to call it a "runaway" situation.

    But some may disagree. Boosting a warming of +6ºC up to +9ºC perhaps would not constitute "runaway" if human civilisation will have been ajudged to have already suffered that "wheels-fallen-off" situation without the additional natural feedbacks.

    I don't know if that is helpful in the response set out @735.

  38. Agreed with MA Rodger.

    No Venus-syndrome for the Earth:

    "With the more realistic physics in the Russell model the runaway water vapor feedback that exists with idealized concepts does not occur. However, the high climate sensitivity has implications for the habitability of the planet, should all fossil fuels actually be burned.

    Furthermore, we show that the calculated climate sensitivity is consistent with global temperature and CO2 amounts that are estimated to have existed at earlier times in Earth's history when the planet was ice-free.

    One implication is that if we should "succeed" in digging up and burning all fossil fuels, some parts of the planet would become literally uninhabitable, with some time in the year having wet bulb temperature exceeding 35°C.

    At such temperatures, for reasons of physiology and physics, humans cannot survive, because even under ideal conditions of rest and ventilation, it is physically impossible for the environment to carry away the 100 W of metabolic heat that a human body generates when it is at rest. Thus even a person lying quietly naked in hurricane force winds would be unable to survive.

    Temperatures even several degrees below this extreme limit would be sufficient to make a region practically uninhabitable for living and working.

    The picture that emerges for Earth sometime in the distant future, if we should dig up and burn every fossil fuel, is thus consistent with that depicted in "Storms" — an ice-free Antarctica and a desolate planet without human inhabitants"

    So no runaway. But Hansen notes that it won't take a runaway to basically completely eradicate civilization as we know it.  Supported by this:

    "While dominated by anthropogenic forcing in these recent times, solar variability in prior eras caused much larger relative influences.

    The early Sun was approximately 70% as bright as at the present when it joined the main sequence about 4.6 billion years ago with a current rate of increase in luminosity of 0.009% per million year (Hecht 1994). At this rate, it will take 10 million years for the background solar brightness to increase by the 0.1% typical of a solar-cycle variation, and another 3.5 billion years for heating from the Sun to create Earth-surface conditions similar to those of the present-day Venus; although additional effects, such as feedback from enhanced ocean evaporation, may accelerate this warming and make the Earth uninhabitable (at least to present-day complex lifeforms) in about one-billion years."

  39. If CO2 caused the temperature to change, (and is resposible for the climate historically) what caused the CO2 to change? Volcanoes? Is there any geological evidence to support this theory?

    Why do the ice-ages and deglacial period occur cyclically, approximately every 100,000 years? Is there some geological pattern identified on earth that would explain cyclical volcanic activity and CO22 emission?

    N.B. The ice-ages coincide with one of the Milankovitch cycles - the eccentricity of the earth's orbit, which goes through cycles of approx. 100,000 years. If the earth periodically gets further away from or closer to a hot object, this should have some influence on the earth's temperature, correct? 

    Response:

    [PS] See here for more on milankovich. In the iceage cycle CO2 is a feedback from an initial albedo-driven driver. Water vapour, albedo and the very slow CO2 feedbacks convert a small change at 65N into a global effect.

  40. Thank you to everyone who responed!

    737@ MA Rodger the man they are talking about is Jim Hansen.

  41. TVC15 @740,

    If it is Jim Hansen, we can track down where he stands on this runaway matter. He said in his book 'Storms of My Grandchildren':-

    “After the ice has gone, would the Earth proceed to the Venus syndrome, a runaway greenhouse effect that would destroy all life on the planet, perhaps permanently? While that is difficult to say based on present information, I’ve come to conclude that if we burn all reserves of oil, gas, and coal, there is a substantial chance we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty”

    This paragraph (I see from Google Books) is a bit of a throw-away at the end of Chapter 10 following a discussion of a boost to AGW from methane hydrates:-

    "If we burn all the fossil fuels, the ice sheets almost surely will melt entirely, ... Methane hydrates are likely to be more extensive and vulnerable now than they were in the early Cenozoic. It is difficult to imagine how the methane hydrates could survive, once the ocean has ahd time to warm. In that event a PTEM-like warming could be added on top of the fossil fuel warming."
    And later, in a Columbia Uni blog page, Hansen explains that he is talking of two things - ☻ The Venus Syndrome runaway (as per the top quote) and ☻ A "mini-runaway" or hyperthermal (as per the lower quote).
    The mini-runaway he decribes as occuring on a millennial scale and which, if we were foolish enough to initiate such an event, could be countered by sequestrating the GHG releases, although there would be a lot to sequester.
    The Venus Syndrome runaway he describes as possibly following on from an un-countered mini-runaway but he ends saying that "Venus-like conditions in the sense of 90 bar surface pressure and surface temperature of several hundred degrees are only plausible on billion-year time scales."

    So this leads to an answer to the question posed by your denialist trolls - Why would 1,200ppm CO2 (Hansen talks of 1,000ppm to 2,000ppm) lead to the Venus Syndrome when in the past it did not?
    Hansen is saying that the 'early Cenozoic' (so before 20 million yr bp) had less methane hydrate which could potentially boost temperatures enough to overwhelm the tropopause and thus allow the leakage of the planet's hydrogen into space, a road that would lead to a Venus-style climate. But importantly, this is on top of AGW. Back in the PETM (44my bp) the fossil fuels were safely tucked away within the geology greatly limiting the potential warming.
    As for previous CO2 levels, there was periods in the past when the fossil fuels of today were still yet to be buried out of harms way & thus CO2 was far higher than 1,200ppm. But that was a long time ago when the sun was a lot fainter and the combined forcing (see this SkS page) would thus be lower than potentially from a mini-runaway today.
  42. jesscars @739,

    The variation of CO2 levels in very ancient times generally resulted from a balance between the amount of carbon being drawn down into the geology by rock-forming and the amount of carbon being ejected by volcanoes. Periods of mountain-building have an impact on that balance, as do periods of extreme volcanism. The results of modelling of very ancient CO2 levels (using GEOCARB III) have been pretty-much supported by the geological evidence.

    The mechanisms that are at work at a more detailed level can be much more complex. Thus the last de-glaciation saw a rise in CO2 levels but that was the product of many different mechanisms, many of which didn't actually work to increase CO2 levels. Thus warming oceans increase CO2 levels but the significant increase in ocean volume as the ice melts into the oceans decreases it. Peat exposed to clmate change releases CO2 while increased bio-activity buries it. (See Ganopolski & Brovkin (2017) for a study of these mechanisms.)

    You also ask specifically about the ice-age cycles. These have been the major feature of global climate for the last 3 million years and until about 1 million years ago they occurred every 40,000 years but now occur every 100,000 years. It is probably best to see ice-ages as being caused by the unstable nature of the full glacial climate. When triggered by the Milankovitch cycles heating the high northern latitudes, an interglacial will result from northern ice sheets melting out. Thus today, if the melt on Greenland were to become enough to drop the summit significantly (a likely event if AGW reached +1.5ºC for a few centuries), the lowered icy-cold top would warm enough to allow more melting and lower it further. Building it back up with new snowfall is a far slower process, so without the return of an ice-age, once ice sheets like the Greenland one begin to go, they go all the way.

    The reason for the change from 40ky to 100ky ice-age timing is not truly understood. The trigger is the Milancovitch cycle, the 40ky from the tilt in axis & the 100ky from a component of the eccentricity variation. One theory is that dust (which increases the sunlight absorbed by ice) was greater in past 40yr ice-ages but now the soils that created that level of dust have been scoured away leaving un-dusty bedrock.

  43. @ 737 MA Rodger

    Dear MA Rodger,

    I deeply appreciate all your knowledgeable responses to my posts with respect to the deniers I deal with! I have learned so much from you!
    With respect to that denier who loves to misrepresent Jim Hansen he also loves to quote mine him and this is exactly what he posts about Jim.  

    I don't understand the mindset of folks who behave in this disingenuous manner.

    James Hansen is the Grand Imperial Kleagle Wizard of Global Warming and he had this to say:

    In his book Storms of my Grandchildren, noted climate scientist James Hansen issued the following warning: "[i]f we burn all reserves of oil, gas, and coal, there is a substantial chance we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty."

  44. TVC15 @743,

    Hansen's book 'Storms of my Grandchildren' is not a scientific work and I have been critical of it for not being scientifc while making overly-bold statements on Sea Level Rise, statements which others take-&-use as being scientific statements. But with both SLR and this Venus Syndrome issue Hansen has made good by later publishing the science. With respect to the Venus Syndrome issue, he references in the Colombia Uni blog (linked @741) the forth-coming paper Hansen et al (2013) 'Climate sensitivity, sea level and atmospheric carbon dioxide' and in particular Fig 7 (below) which shows that above 16 x 310ppm (5,000ppm) the tropopause disappears (the atmosphere stops getting warmer through the stratosphere) which would see the Earth's water begin to leach out into space.

    Hansen et al 2013 Fig 7

    I wouldn't be sure whether burning all the fossil fuel reserves and then precipitating CO2 emissions from the biosphere etc would manage to achieve 5,000ppm CO2 but it is all rather academic. The damage to humanity, indeed to life on Earth would be unconscionable a long way before 5,000ppm CO2 is reached.

  45. LOL the denier is back with his silly statments.

    The entire global warming hypothesis is nonsense.

    If there was any truth to it, then Inter-Glacial Periods would never end.

    The CO2 that supposedly accumulates and causes temperatures to rise ending a Glacial Period should continue to cause temperatures to rise, except it doesn't.

    No matter how much CO2 accumulates, you always end up right back in a Glacial Period.

    Is there any truth to anything this denier is stating?

  46. Deniers favourite tactics are strawman and cherry pick. In case, a strawman. Just because your denier doesnt understand the science of how glacial and interglacial feedback cycles work, doesnt mean that scientists dont either. Insist that your denier quotes the actual science that he is supposedly refuting. The missing link here is suppression of natural methane and CO2 emissions as land (especially eurasian wetland) becomes frozen; and importantly, the increased solution of CO2 in oceans as they cool. Of course, scientist do the hard yards of measurement, modelling (check numbers work), and cross-checking, whereas denier are only interested in hand-wavy dismissal.

  47. TVC15 - if are you continuing to engage with deniers, then please, please take the time to read the IPCC WG1 report so you have a grounding in what the science says. At very least, read SPM.

  48. Thank you Scaddenp!  I will read it! 

  49. TV- he's using flawed logic from word one... your denier pal is not entertaining complexity and (supposedly, lol) thinks the world works in straight lines. Just a rich idiot who does know better because when it comes to money all of a sudden he understands there are multiple factors at play...

  50. TVC15 @745,

    Your denier is of course spouting nonsense. But perhaps it would be helpful to know how to respond to him other than just asking him to generally explain his nonsense.

    I would ask your denialist troll how long he expects the effects of AGW to last. Does he expect CO2 levels to remain for ever? That would be very wrong. Or perhaps only a few tens-of-thousands of years which would be more correct? That, of course, is the time-scale that ice-ages operate on.
    Ice ages are, of course, mainly driven by changing albedo (due to the changing levels of ice reflecting changing amounts of sunlight back into space). CO2 is not the primary driver.

    For a bit more background, we can look back at those ice-age CO2 levels.

    During the last interglacial (the Eemian) the measured peak-CO2 was 287ppm back 128,400 years before present. (This is from EPIC Dome C ice core data.) From this peak, CO2 dropped to 262ppm in the following 1,240 year, a drop which was the first part of a set of oscillations measured between 280ppm and 260ppm that continued for 15,000 years after the peak. It was only following those oscillations that CO2 began to fall back towards 200ppm, the bulk of this decline (a drop to 230ppm) taking 7,500 years.

    We can compare the drop from that ice-age driven CO2 pertubation with the expected future of our own CO2 anthropogenic pertubation. That ice-age pertubation was (287 - 195 =) +102ppm over 8,000 years while out anthropogeinc pertubation is so-far (410 - 280 =) +130ppm over roughly 100 years.
    The likes of Archer et al (2009) 'Atmospheric Lifetime of Fossil Fuel Carbon Dioxide' suggest that roughly 80% of an instant CO2 pertubation would be absorbed into the oceans in roughly 1,000 years. (Lord et al 2016 Fig 4 suggests it would be a little higher for our present 600Gt(C) level of emissions, perhaps 87%.) About 55% of our anthropogenic pertubation has already been absorbed so if our CO2 emissions stopped we would expect today's CO2 levels to drop roughly 70ppm over 1,000 years or so, being absorbed mainly within the oceans. But the rise of the ice-age pertubation of the Eemian was far slower than our pertubation (8,00y against 100y) so we can simplistically assume that all the +102ppm represents that remainng 20% of the actual ice-aged-forced emissions. (In reality, much of the CO2 in the ice-age pertubation has been driven from the oceans so will not be re-absorbed there over such timescales.)

    That remaining 20% (& bulk of the Eemian +105ppm) is expected would slowly be absorbed over following millennia, but surely not as quickly that 7,500 year Eemian period which saw perhaps a 10% drop (of the assumed total ice-age pertubation). This would concur with the proposed reversal of much of the pre-Eemian ice-age driven CO2 increase as the new ice-age develops, when the oceans begin to re-absorb CO2, along with a whole lot of other mechanisms that operate on CO2 through the ice-age cycles.

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