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The climate has always changed. What do you conclude?

Filed under: — stefan @ 20 July 2017

Probably everyone has heard this argument, presented as objection against the findings of climate scientists on global warming: “The climate has always changed!” And it is true: climate has changed even before humans began to burn fossil fuels. So what can we conclude from that?

A quick quiz

Do you conclude…

(1) that humans cannot change the climate?

(2) that we do not know whether humans are to blame for global warming?

(3) that global warming will not have any severe consequences?

(4) that we cannot stop global warming?

The answer

Not one of these answers is correct. None of these conclusions would be logical. Why not?

(1) The opposite conclusion is correct: if the climate had hardly changed during the course of the Earth’s history (despite variable incoming solar radiation and changing amounts of CO2 in the atmosphere), then we would conclude that there are strong stabilizing feedbacks in the climate system. The drastic climate changes in the history of the Earth (ice ages, hot ice-free periods) show that the climate system is sensitive to changes in the radiation budget. The measure for this sensitivity is called climate sensitivity: how much global warming will result from a CO2 doubling in the air? For the first time it was estimated by the Nobel laureate Svante Arrhenius in 1896. According to our modern knowledge this climate sensitivity is around 3°C (uncertainty ± 1°C).

Paleoclimatologists determine the climate sensitivity from data from the Earth’s history. A recent review article in Nature on this method showed “a warming around 2.2 to 4.8 °C per doubling of atmospheric CO2, which agrees with IPCC estimates”. In short: the larger past natural climate changes have been, the more vulnerable is the climate system, and the more it will react to the greenhouse gases that humans are adding to the system.

(2) Imagine there has been a forest fire. The police have extensive evidence that it was arson. They know the place where the fire began. They found traces of fire accelerants. Witnesses observed a man whose car was parked nearby. In his trunk the police finds bottles with fire accelerants, and in his house they find even more of it. He has been convicted for arson several times before. Plus some further evidence. In court, he defends himself: forest fires have always occurred lit by lightning, even before there was any man on Earth. Therefore he must be innocent. Does the argument convince you?

The evidence for the human cause of global warming is overwhelming. This is why there has been a consensus among climate researchers for a long time, and almost every scientific academy on the planet has come to the same conclusion. The most important evidence: when it gets warmer, the energy has to come from somewhere (1st law of thermodynamics). It can only come through the radiation budget of our planet. (No, Rick Perry, the energy does not come out of the ocean. To the contrary, measurements show heat is going into the oceans). The changes in this energy balance are quite well known and are shown near the front of any IPCC report – see Fig. 1. The biggest factor is the increase in CO2 concentration as well as a few other greenhouse gases, also added by human activities. The incoming solar radiation has changed just a tiny bit in comparison – since 1950, by the way, it has even decreased and thus offset a small part of the human-caused warming – hence humans have probably caused more warming than is observed (best estimate is 110% of observed warming).

Fig. 1 Radiative forcing is the cause of global temperature changes. Red bars show warming, blue bars cooling effects. I am showing the diagram from the fourth IPCC report of 2007, because it is easier to understand than the more recent from the 5th IPCC Report of 2013, which Gavin discussed here. The overall human-caused radiative forcing, which is given here as 1.6 watts per square meter, had already risen to 2.3 watts per square meter by the year 2011 according to the 5th IPCC report. Source: IPCC report 4 Fig. SPM.2.

Overall, humans have caused an additional heating (radiative forcing) of 2.3 watts per square meter of Earth surface – as of 2011. It has increased further since.

(3) Those who can’t deny that humans are causing warming often seek refuge in the hope that the consequences might not be so bad, so we might just adapt rather than having to stop further warming. The climatic changes in Earth’s history do not support this point of view. As a result of the global warming by around 5 ° C from the last ice age 15,000 years ago to the mid-Holocene, global sea levels rose by 120 meters until 5,000 years ago! At that time hardly a problem – but for today’s humankind even a rise of two meters would be a disaster, bringing devastation to coastal cities and small island states. We still have enough ice on Greenland and Antarctica to raise the sea level around the world by 65 meters. Both ice masses are losing ice more and more quickly. The West Antarctic has probably already crossed its tipping point and is unstable. Greenland could soon follow.

Fig. 2 Ice loss of Greenland measured by GRACE satellites. Source: NASA .

By the way: the just mentioned 5°C rise within ten thousand years at the end of the ice age are among the fastest global temperature rises documented in the Earth’s history. That is 0.05 degrees per century. In the last hundred years we have caused the twentyfold rise. This pace of change overtaxes the adaptability of many ecosystems and will lead to their collapse as the warming progresses. In coral reefs this is already in progress.

The pace of the completely man-made CO2 increase (by now the CO2 concentration is higher than at any time in the past three million years) leads to a rapid acidification of the world’s oceans, because it overcomes the buffer capacity of the oceans. The last major acidification event 250 million years ago has apparently led to a massive extinction of species in the world’s oceans.

(4) Often I hear that the aims of the Paris Climate Agreement are absurd, because humans cannot stabilize the global temperature – after all, our climate changes even without human intervention. This argument is also wrong. As already mentioned, without human interference there would have been no global warming since the middle of the 20th century. If anything there would have been a slight natural cooling. The fluctuations in the sun’s activity are causing variations of 0.1 or 0.2 °C in global temperature in the last thousand years (e.g. at the Maunder Minimum of solar activity in the years 1645 to 1715). In the longer term, the astronomical Milankovitch cycles of the Earth’s orbit and the Earth’s axis dominate the natural climate changes (hence the ice ages). The shortest of these cycles has a period of 23,000 years – for the next hundred years, it practically does not matter. However, our fortune would last much longer than that: the Milankovitch cycles can be calculated over millions of years with astronomical precision (and incidentally be used to predict the beginning of all the past ice ages), and according to that, the next major climate change would arrive only in about 50,000 years. Namely the next ice age.

So if we weren’t doing something really stupid, we could benefit from another 50,000 years with a stable climate. Nothing in our knowledge of paleoclimatology suggests that natural factors could prevent us from limiting global warming to below 2°C. Only our own dithering, our own inertia can do that. Or that we prefer to be lulled into fatal complacency by the reassuring fairy tales of the “climate skeptics” rather than confronting the danger.

Among the most ill-informed claims of those “skeptics” is the assertion that climate researchers do not know or consciously ignore the fact that the climate has always changed. Utter nonsense, of course. Almost all of the authors here at Realclimate have done substantial work in paleoclimate for decades, as you can see from our publication lists (including the textbook Paleoclimatology). A lot of other climate researchers do the same. This May, three of us were at a conference of almost one thousand paleoclimatologists in Zaragoza (see photo below). These researchers know more about the natural, past climate changes than anyone else. Nobody there expressed any doubts about the ongoing human-caused global warming. On the contrary, many paleoclimatologists are particularly concerned about anthropogenic warming, especially in view of our findings about Earth’s history. Already when I was working as lead author on the paleoclimate chapter of the 4th IPCC report more than a decade ago, some of the discussions within IPCC revolved around us paleoclimatologists regarding some risks as considerably more serious than the colleagues specializing in the modern climate, such as the risk of rapid sea level rise or instability of ocean currents and ice sheets.

Whoever tells you that the fact that “the climate has always changed” is somehow reassuring, does not know what he is talking about – or he is trying to con you.

Paleoclimatologists: participants in the PAGES Open Science Meeting in Zaragoza in May 2017

 

243 Responses to “The climate has always changed. What do you conclude?”

  1. 51
    Thomas says:

    43 Dan DaSilva, please stop your insulting psychological projection of your own arrogance onto climate scientists and RC readers. If you’re here for an intellectual battle it would help to come armed with some intelligence and an awareness of your own dire limitations.

  2. 52
    Thomas says:

    44 Keith Woollard says: “Explain the past with your simplistic CO2-drives-everything model and I will trust you.”

    Either disingenuous or foolish or blinded by cultural / geological / a lifetime’s investment in FF Corps personal BIAS? It’s so hard to tell.

    There is NO ‘CO2-drives-everything model’ Keith. So why are you publicly LYING about that or intentionally obnubilating the actual facts of the matter by presenting SPURIOUS FALSEHOODS?

    Can you not comprehend the most basic aspects of modern climate science Keith? Apparently you cannot!

    Are you seriously claiming to be a trained competent science based expert in fossil fuel geology? To me you sound like a rank dill who trundled up drunk at a party uninvited. :-)

    And why assume that anyone needs your trust in the first place? You’re not that important to climate scientists and paleontologists mate. :-)

    This article by Stefan sure has stirred up the climate whackos of the world that’s for sure. As usual nothing is gained, and no improvement will be seen among the most invested in their delusions and dunning-krugar level incompetence. (shrug)

    Mike has it right ….. why even bother? Pigs love mud.

  3. 53
    Andrew says:

    Re: #7 “a troll spreading propaganda”

    I am not sure what is the exact purpose of posting such blatant lies in this comments section.

    “There is strictly no evidence (and actually rather a lot against) that 7+ billion people might ever live in a decent way on renewable or even nuclear energy.”

    Exactly the reverse is true! There is plenty of evidence that we have to stop using fossil fuels and that 100% renewables are the only real alternative for supplying the energy needs of 7+ billion human beings. You can even show that switching to renewables from fossil fuels will grow the global economy and improve people’s health and well being.

    “Curbing massively the fossil fuel use means most likely harming and eventually killing the poor and even middle classes…”

    Again, exactly the reverse is true. The biggest consumers of fossil fuels and consequently emitters of GHG’s are the rich, the ultra-rich and the military. The poor and the middle class (that is, the vast majority of us) have strictly nothing to lose and everything to gain from abandoning fossil fuels and switching to renewables.

    A carbon fee + dividend scheme such as suggested by James Hansen would not only go a long way to “curb massively the fossil fuel use”, but it would also have the added beneficial effects of slightly redistributing income, improving public health, stimulating the economy and greatly accelerating the inevitable transition to renewable energy.

  4. 54
    Ken Fabian says:

    Mr KIA – It is negligent of people holding positions of trust and responsibility to fail to heed the consistent and persistent expert advice – the advice they commissioned so they could be sure before taking significant action and commissioned a review of to be sure the first advice was sound before committing to anything and commissioned a Red Team/Blue Team face off to give the Red Team a chance to take advantage of 99% of viewers .. err voters having a clue before doing anything. I’m not sure we can afford that degree of responsibility avoidance in people we ought to be able to rely on.

  5. 55
    Marco says:

    Dan DaSilva @43, ever considered the exact opposite: that we are changing the climate even more than those ‘arrogant’ climate scientists make us believe?

    If not, why not?

  6. 56
    patrick says:

    #43 Dan DaSilva: So what you conclude is that the fact presents an opportunity for lousy rhetoric. Take out the cheap shots and name-calling (such as “arrogant,” and “desperately”), and try something in the neighborhood of reason.

  7. 57
    Victor says:

    #46 bjchip sez: “The formal logic problem precludes ANY conclusion based on the argument of the form X has always happened therefore we cannot be causing X.”

    Nice try. But you’ve got things backwards. No one is arguing that, because climate is always changing, CO2 cannot be responsible for the changes we see today. That’s a straw man for sure. Skeptics need not make such an argument in any case, because it’s the presenter of the hypothesis who has the burden of proof, NOT the one assessing it.

    Turn things around. Supporters of the mainstream climate change hypothesis claim there is no explanation for the (supposedly) alarming rise in temperatures other than CO2 emissions, and they challenge skeptics to provide one. As a response, skeptics have noted that the climate has always changed and that the temp. rise we see today is most likely nature behaving as usual. I see no logical flaw in that argument. Once again, burden of proof is on the supporter of the hypothesis, NOT those evaluating it.

  8. 58
    Alastair McDonald says:

    Keith Woollard @44 wrote:

    “I am a geophysicist, all my income for my 30 years of professional life has come directly or indirectly from the oil and gas industry.”

    “The reason I would use “the climate always changes” as an argument is to say that the earth’s climate is a very complex beast that we are just scratching on the edges. Explain the past with your simplistic CO2-drives-everything model and I will trust you. I am not talking about major P-T transitions or ice ages from solar cycles, explain to me finely interbedded sand-shale sequences.

    …. and don’t listen to people like Alastair@18 try and explain geology !!”

    Here is an example of an interbedded sand-shale sequence produced by climate change: The Late Glacial and The Younger Dryas-Preboreal boundary. BTW, there was no CO2 involved.

  9. 59
    Mitch says:

    #44 Keith: You make an odd argument. What geologists/geophysicists learn is that the physics of earth processes don’t change, not that the processes were the same. It is a significant difference. When I have seen the “climate has always changed”, it has almost invariably been used to argue that somehow human-produced greenhouse gases cannot force climate, so that the observed change is somehow “natural”. And, they follow by saying temperatures were warmer in the Jurassic or some other irrelevant point. Never mind that the continents were in a different place and ocean currents were different. So also were the surface carbon reservoirs.

    You finish by saying that you don’t believe that we can understand climate why you lack belief that science can be used to study climate. Since you are a geophysicist, you should actually read what the IPCC reports say. You would find that the models are not “simplistic CO2 drives everything”. In terms of explaining how climate works, I think that AR3 does the best job, while AR4 and AR5 synthesize the new studies that constrain the parameters.

  10. 60
    Obstreperous Applesauce says:

    Dan DaSilva says:
    20 Jul 2017 at 10:23 PM
    “The climate has always changed.”

    This fact along with other observations allows you to conclude:

    (5) that humans may not be changing the climate as much as some arrogant climate scientists desperately want you to beleive.

    Let’s take out the weasel words and unsubstantiated assertions, which render your comment meaningless, and just write what you really mean.

    “The climate has always changed.”

    This fact…allows you to conclude:

    (5) that humans…not be changing the climate….

    So, false.

  11. 61

    Aido 10: Consensus belongs in religion, not in science.

    BPL: Peer review and the scientific consensus are how modern science work. That is the system that placed six two-man crews on the Moon, sequenced the human genome, and built the computer you’re using to post here.

  12. 62

    KIA 34: our average earth temperature estimates older than 100 years are suspect at best.

    BPL: Who says? You?

  13. 63

    DDS 43: humans may not be changing the climate as much as some arrogant climate scientists desperately want you to beleive.

    BPL: Who is more arrogant? The climate scientist who talks about findings in his/her field? Or the uneducated politics junkie who never took a relevant course, but thinks he/she knows better than the scientist. To say your uninformed, ignorant opinion is just as valid as that of an informed, educated person–on the subject in question–strikes me as the more arrogant conduct of all.

  14. 64

    KW 44: Explain the past with your simplistic CO2-drives-everything model

    BPL: We don’t have any such model. Straw man argument.

  15. 65
    Hank Roberts says:

    > Woollard … Explain the past with your simplistic CO2-drives-everything model and I will trust you.

    This is just sad. Can’t you do better?

  16. 66
    nigelj says:

    Victor @53

    “As a response, skeptics have noted that the climate has always changed and that the temp. rise we see today is most likely nature behaving as usual. I see no logical flaw in that argument.’

    Fine as far as it goes. But pretty much a strawman. Logic is important, but not the same as not scientific evidence. We then ask sceptics to test their “logical assumption” and show in detail which natural forces are causing current climate change, and they cannot, because solar activity is flat etc.

    We propose an alternative greenhouse gas theory with strong evidence and they cant work it out. They go back to chanting “climate changed before”. Conclusion, they are dumb, stubborn, or ideologically motivated or all three.

    By the way, that was a lesson in application of logical deduction.

  17. 67

    V 53: Supporters of the mainstream climate change hypothesis claim there is no explanation for the (supposedly) alarming rise in temperatures other than CO2 emissions, and they challenge skeptics to provide one.

    BPL: That’s because they’ve examined all the possible causes. Have you ever heard of “analysis of variance?”

  18. 68
    tadaaa says:

    the “climate always changed” meme was used because it was so effective

    it has a simplistic truth that conspiracy theorists and science deniers find attractive, no further thought required

    it is similiar to the 911 twoofer meme that the “towers fell straight down”

    a simplistic truth and slam dunk proof of CD to a twoofer – but simply describing the force of gravity to anyone who gives it more than a seconds thought

  19. 69
    nigelj says:

    Keith Woollard the geologist @44

    “Explain the past with your simplistic CO2-drives-everything model and I will trust you.”

    Big huge strawman there Keith. Possibly a petrified, fossilised one. Climate models use a large range of factors, not just CO2.

    Past climate is known to have a range of influences, and it evolved over time as well. It’s complex to untangle, but not impossible.

    But geology is a fine thing. I nearly did a degree in it, but not enough jobs at the time.

  20. 70
    Bob Loblaw says:

    Keith Woollard says “I am therefore a shrill of big oil and my opinion is worthless.”

    No, Keith: your opinion is worthless because it is so often wrong.

  21. 71
    Thomas says:

    68 tadaaa, so true that climate science denial is directly equivalent to 9/11 Truthers, Birthers, end of the world prophecies, young earthers and the like.

    Not an ounce of reason, logic, evidence, or truth in the whole lot of them. Nutters pure and simple, including the recent uptick in comments right here. Rank delusional fools one and all. It’s quite pathetic. And people then go and vote for fools just like the ignorant trolls here. How humanity has survived even this long is incomprehensible to me some days.

  22. 72
    nigelj says:

    Tadaa @68, true.

    In fact highrise buildings are designed to fall straight down, and its also partly in their nature to do this anyway. Their structure is more of a stack of components than a rigid object like a tree. People just assume they would act like a tree.

    Assumption is the root of all problems. Well a lot of problems.

    The plane jet fuel exploded within the twin tower weakening the immediately adjacent structural floor and column elements, collapsing them. Then the full weight above crashed down taking down everything floor by floor. It was one of the most shocking things I have ever seen.

  23. 73
  24. 74
    Chris O'Neill says:

    the “climate always changed” meme was used because it was so effective

    That’s why we should have stuck with using the term “global warming”.

    “There has always been global warming” just doesn’t seem to come out right.

  25. 75
    Chris O'Neill says:

    #23 Victor:

    I see no evidence of a long-term correlation between CO2 emissions and temperature.

    Why don’t you get a list of CO2 levels and global temperature anomalies for each year since 1910 and see what correlation they have? Then we’ll be able to tell if you’re so blind that you will not see.

    BTW, atmospheric CO2 increased by 3.6% from 1910 to 1940 and by 4.6% from 1940 to 1970. According to you Victor, a 3.6% increase is a “low rate of increase” while a 4.6% increase is “rising sharply”. You are obviously biassed Victor.

  26. 76
    Adam Lea says:

    Re 22: I appreciate that mass cooperation to solve an impending threat can happen e.g. the Y2K bug or Hitler. The key difference with AGW is that the primary cause is the wasteful and unsustainable Western lifestyles. To solve the problem relies upon people willing to fly in the face of the human utopia which is freedom without responsibility, and address their way of living. This has to happen without a visual threat, and requires sacrifices on an individual level without any perceived benefit (e.g. when I cycle to work instead of drive, it does nothing measurable to decrease traffic congestion or pollution, but it does elevate my vulnerability, increases journey time and increases fatigue). That is what makes AGW such a super evil problem, you are ultimately asking people to take a hit on perceived quality of life for no perceived benefit. Note that it is perception that matters, not facts (because we are emotional, not logical beings).

    It matters not how many people agree climate change is happening and that humans are primarily responsible. What counts is what they do based on that knowledge, and I see little evidence of much happening of any significance. People are still voting for right wing neo-liberal capitalist governments, and if anything, the right wing (which is more likely to deny AGW) is becoming stronger (think demonisation of immigrants and Brexit). I wish I could be more optimistic but can’t find any based on my observation and interaction with people.

  27. 77
    Evans says:

    The climate has always changed and life changed in response. How will life adapt this time? Harmful algal blooms and Zika are just the beginning. Each species thrives under a given set of conditions (pH, temperature, gas content) and humans are on course to test those limits. For all the talk of our higher brain functioning, we are profoundly stupid.

  28. 78
    Victor says:

    #66 nigelj: “We then ask sceptics to test their “logical assumption” and show in detail which natural forces are causing current climate change, and they cannot, because solar activity is flat etc.”

    You missed the point. A sceptic need not have a “logical assumption.” It is the proposers of the theory who are the ones with the assumption, and it is their responsibility to “show in detail” that their assumption is in accordance with the facts and that no other explanation is possible. That’s a tall order. Remember: the burden of proof is on the defender of the theory, not the one evaluating it. This is basic epistemology — see, for example https://en.wikipedia.org/wiki/Philosophical_burden_of_proof#Holder_of_the_burden

    For example, someone attempting to prove the existence of leprechauns could challenge skeptics to “show in detail” that they do not exist, which is, of course, a completely unreasonable request. Does this mean that leprechauns actually do exist? I don’t think so.

    By adopting a similar tactic, supporters of the mainstream view risk committing the logical fallacy known as “argument from ignorance.”

    “One way in which one would attempt to shift the burden of proof is by committing a logical fallacy known as the argument from ignorance. It occurs when either a proposition is assumed to be true because it has not yet been proved false or a proposition is assumed to be false because it has not yet been proved true.” (Same source as above.)

    After spending a good deal of time and effort researching the epistemological issues behind the climate controversy in preparation for my book, I concluded that the essence of the “alarmist” position is precisely the argument you’re attempting to make. I.e., that CO2 emissions from fossil fuels must be largely responsible for the run-up in global temperatures, because all other possibilities have been investigated and none are sufficient to produce the observed results on their own. And since CO2 emissions appear to be the only other force capable of driving temperatures upward, it is they which must be responsible.

    In other words, CO2 must be the culprit because we cannot think of any other possibility. Just as leprechauns must exist because we cannot prove they don’t. Classic argument from ignorance. And once again, as a skeptic all I need do is utter the much maligned, but perfectly reasonable formula: “the climate has always changed.” If, in fact, the climate HAS changed over the millions of years of Earth’s history (it has), and if, in fact, we are not always able to explain why it has changed (we aren’t), then I see no reason to accept the assumption that CO2 has to be the principal driving force.

  29. 79
    tadaaa says:

    @ nigelJ

    indeed nutters the lot of them

    the other one that makes me giggle is the Chemtrailers who bang on about the levels of Aluminium in the soil – after a heavy dose of “spraying” they send soil samples to be tested – and then post result that show high levels of aluminium

    oblivious to the fact that aluminium is the most common metal in the earths crust

    again like the “climates changed before and the towers fell straight down” brigade they are just confirming what science has known for centuries

  30. 80
    t marvell says:

    There is another common denier reasoning: God made earth for mankind, so he/she would never allow a global warming catastrophe. The scientists’ contentions have to be wrong (just as evolution theory must be wrong, which a large minority of people believe).
    No matter of scientific discussion will dent this mind set.
    Sociologically, this mind set is part of the resentment against the establishment, which is behind those (except the rich) who voted for Trump.

  31. 81
    John Pollack says:

    One hot morning near a remote village at the edge of a large forest, a group of villagers discovered a strange large animal in a clearing, apparently asleep. They went back and inform the village elders, who called in the local chamber of commerce, and also summoned the only biologist in the region.

    Later, the biologist arrived and reported back to the village. “This is a very dangerous situation. That animal is a large predator. It has huge canine teeth, an absence of molars, eyes relatively close together for focused hunting, and large claws. My best estimate from the body pattern is that it is a large feline. Judging from the stripes, it is a “tiger”. While it is still asleep, it will wake and hunt, perhaps tonight. I got a rough reading from my infrared camera, and its metabolism seems consistent with a large cat. You would do best to evacuate the village, but you MUST keep a large distance, and DO NOT DROP OBJECTS ON ITS TAIL.”

    The chamber of commerce spokesperson replied “Don’t listen to this alarmist! It’s a good thing that we invested in an internet satellite station for the village. The pictures of locals dropping sand on its tail have gone viral. We’re making tons of money and creating jobs. Next step is pay-per-view when they drop something bigger. Besides, the epistemology of this job-killing so-called expert is completely warped. The teeth and claws could be for symbolic threat displays during mating season. Besides, you haven’t even observed it move, let alone what it eats. It may not even have any nerves in its tail. We suggest that it’s an estivating herbivore that will be in a torpid state for months, and slow-moving when it does awake.”

    The biologist exclaimed “This is nonsense! It can’t be an herbivore with those teeth, and cats have never been observed to estivate, although they do sleep a lot after a large meal.”

    The chamber spokesperson scoffed “You haven’t even proven it’s a cat. You’ll need an autopsy or a DNA sample for that. You didn’t get one, did you? You haven’t even demonstrated that it has nerves in its tail. They’re your assumptions, and you’re obliged to demonstrate them. Otherwise, it’s the null hypothesis that it’s not dangerous, won’t wake for a long time, and has no nerves in its tail. You’re illogical. Leave now.”

    “Leave now, leave now,” the villagers chanted.

    The pay-for-view was the sensation of the season, but nobody from the village ever appeared at the big city bank to collect their money.

  32. 82
    CCHolley says:

    #78 Victor:

    “that CO2 emissions from fossil fuels must be largely responsible for the run-up in global temperatures, because all other possibilities have been investigated and none are sufficient to produce the observed results on their own. And since CO2 emissions appear to be the only other force capable of driving temperatures upward, it is they which must be responsible.”

    “In other words, CO2 must be the culprit because we cannot think of any other possibility. Just as leprechauns must exist because we cannot prove they don’t. Classic argument from ignorance.”

    Wrong. Straw man. Unlike a belief in leprechauns, there is a preponderance of evidence that CO2 warms the planet and that the anthropogenic contribution of CO2 to the atmosphere is causing the observed warming trend. Not only is there a preponderance of evidence, that evidence is quite compelling. The fact that no other forcing can account for said warming is not the logical argument for the veracity of the theory, it is only one piece of information that confirms the conclusion that all of the other evidence points to. Yawn.

  33. 83

    V: A sceptic need not have a “logical assumption.”

    BPL: You said it, we didn’t.

  34. 84
    nigelj says:

    Victor @78

    “It is the proposers of the theory (agw climate change) who are the ones with the assumption, and it is their responsibility to “show in detail” that their assumption is in accordance with the facts and that no other explanation is possible. That’s a tall order.”

    The “warmists” are not making an assumption. They are reaching a measured, evidence based conclusion and have done well enough to convince me.

    Basically natural forces have driven climate in the past but theres no evidence they are causing recent warming. Increasing greenhouse gases from fossil fuels are good evidence and consistent with whats happening in the atmosphere in terms of various changes.

    Of course its always possible we have missed some mysterious natural cycle that could be operating right now to cause warming, but scientists have had a close look at every possibility they can think of from solar cycles, ocean cycles, geothermal energy, cosmic rays and ruled them out. I think the chance they have missed something is vanishingly small. The world is driven by physical mechanisms and there are only so many of these. Only so many possibilities.

    “For example, someone attempting to prove the existence of leprechauns could challenge skeptics to “show in detail” that they do not exist, which is, of course, a completely unreasonable request. Does this mean that leprechauns actually do exist? I don’t think so.”

    You are right, but have applied this incorrectly to the global warming issue.

    Its the denialists claiming there must be a “hidden cause” and you cannot disprove this, which is of course an absurd position to take. You could do the same for tobacco smoking, almost any science theory.You have to look at weight of evidence and plausible causes.

  35. 85
    Chris Crawford says:

    “For tens of thousands of years, millions of people have always died from natural causes. Therefore, the corpse in the alley with a knife sticking out of its back could not have died from anthropogenic causes.”

  36. 86
    Chris Crawford says:

    Victor @ #78:

    You err in assuming that AGW is a philosophical issue. It is not; it is a scientific issue. In science, we attempt explain phenomena with hypotheses that specify models showing the operation of the phenomenon in question. We always have multiple competing hypotheses, although in the initial stages, none of those hypotheses may have strong evidence to support it.

    The undeniable fact is that the planet is warming, that sea level is rising, and a number of other climate changes are taking place. We have one hypothesis to explain it: anthropogenic global warming. It has garnered a monumental amount of supporting evidence. You appear to propose that there is no explanation for the observations — in other words, that the observed changes are, perhaps, God’s work, or perhaps just an accident. Both of those hypotheses are manifestly absurd. Until you can come up with a better hypothesis, our strongest hypothesis remains AGW.

    And your leprechaun analogy is completely off the mark because there are no observations of leprechauns. There ARE petabytes of observations demonstrating that the earth truly is undergoing climate change.

  37. 87
    Mal Adapted says:

    Bob Loblaw:

    No, Keith: your opinion is worthless because it is so often wrong.

    Dang. Mr. Loblaw has a few things to teach me about the soul of wit 8^}!

  38. 88
    Mal Adapted says:

    Mack:

    If you now go to Wikipedia and look up the definition of “Radiative Forcing” you will notice that the wording has now changed ..so that the first sentence has been eliminated.
    Seems that the dishonest alarmist running Wiki, was a little embarrassed.

    Mack illustrates the ‘self-sealing’ character of conspiracist ideation perfectly: nothing a climate scientist does can have a non-sinister explanation. He also makes explicit the universal a priori assumption of climate conspiracists: climate realists are all ‘dishonest alarmists’.

  39. 89
    Mal Adapted says:

    Barton Paul Levenson:

    V: A sceptic need not have a “logical assumption.”

    BPL: You said it, we didn’t.

    Barton appears to have grasped the soul of wit also ;^).

  40. 90
    Thomas says:

    83 BPL …. rotflmao!

    Did he really write a book on his high degree of ignorance? :)

    Tip for Victor: Only 1 left in stock – order soon.
    https://www.amazon.com/exec/obidos/ISBN=1905177070/roberttoddcarrolA/

    could this skeptics guide help him?
    Structure of a Logical Argument
    http://www.theskepticsguide.org/resources/logical-fallacies

    OR terms like “skeptic” and “open-minded” are often misappropriated by people in the anti-science movement, and many of the most biased people on the planet are under the delusion that they are skeptical.
    https://thelogicofscience.com/2015/04/02/what-does-it-mean-to-be-a-skeptic/

    Et Tu Victor?

  41. 91
    CCHolley says:

    nigelj @ 84 re. Victor

    “Of course its always possible we have missed some mysterious natural cycle that could be operating right now to cause warming, …”

    Ironically, it is far more likely that there are leprechauns than that there is some unknown yet to be discovered climate forcing.

  42. 92
    John Mashey says:

    Good piece by Stefan.

    It’s worth looking at Skeptical Sciences’ fixed list of arguments, where “climate’s changed before” is #2, i.e., it’s an old one, but by current popularity it’s #1!

    This false meme seems to have gotten an early boost ~1991 in MedievalDeception 1991: Lindzen Hijacks Curve For Western Fuels Video – Early Fake News.

    Stefan linked to Ray Bradley’s fine book Paleoclimatology 3rd Ed, which painstakingly describes the challenges and techniques for extracting signal from paleo noise. The 2nd Ed was the one plagiarized/altered in the Wegman Report. It is also amusing to see critiques by people who have no idea their concerns were being addressed decades ago by pro’s.

    As for the future, David Archer’s The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth’s Climate is an easy read. Depending on how much CO2 we emit, we may even miss the next shot at ice age, 50Ky off. In any case, not soon.

    For another view on the radical differences of our interglacial versus past ones, see Ruddiman, Kutzbach, Vavrus (2011), of which Figure 6 is a good summary.
    For more, see Bill’s book
    Earth Transformed(2013) or watch his 2013 AGU Tyndall Lecture.

    Bill did an update here at RC a year ago.

    To summarize some of the discussion in this thread:
    Pseudoskeptics Are Not Skeptics.

  43. 93
    nigelj says:

    CCHolley @91

    “Ironically, it is far more likely that there are leprechauns than that there is some unknown yet to be discovered climate forcing.”

    Yes true. I know highly intelligent tobacco smokers who still believe cigarettes don’t cause disease, that its some hidden factor despite the strong evidence tobacco causes disease. Its a feature of drug addiction. Fossil fuel use may have some characteristics of an addiction, or at least an ingrained habit.

    I think addiction probably exists on a continuum, and we can be addicted to almost anything that causes pleasure and triggers dopamine receptors in the brain. So people may get attached to fossil fuels at a deeper, addicted level and probably aren’t consciously aware they are. This would be significant if you were a car owner for example. Perhaps entire societies and their institutions can develop addictions.

  44. 94
    Mr. Know It All says:

    There is no such thing as a “science denier”. You cannot deny that which you do not know and almost no one understands the AGW science details (except climate scientists). You can be skeptical though. If a scientist who does understand AGW science says it is not proof of warming he is not denying science, he’s denying the conclusions some have made, or the methodology used to reach those conclusions, etc.

    72 Nigel
    The jet fuel exploding did not do the damage, it was the loss of strength in the building structural steel, due to heat of the burning jet fuel which caused the collapse.

    76 Adam
    “….think demonisation of immigrants and Brexit….”
    If you don’t understand WHY uncontrolled immigration resulted in Brexit then you must be living under a rock. I suggest you spend 1 minute in the AM, and 1 in the PM every day, reading the headlines at http://pamelageller.com/
    Let us know your thoughts after that little exercise.

  45. 95
    John Monro says:

    Thanks for the article.

    There’s two serious common logical fallacies rolled in to one in this argument “The Climate’s Always Changed”. And if any one was silly enough to argue agains global warming on this basis, this is what I’d say

    1) How do you know the climate’s always changed? Are you a palaeoclimatologist who’s done the original research? If not, the only way you can suppose that climate has always changed (which wasn’t common knowledge until the last one hundred years) is by agreeing with the research and opinion of many climate scientists and others, who have built up a picture of a constantly changing climate over the history of this planet. But IT”S THE SAME SCIENTISTS USING THE SAME SCIENCE who are telling you we are now changing this climate. Why do you argue one opinion, but deny the other? Why do your argue one half of the science and deny the other half of the exactly the same science??? It’s a form of intellectual cherry picking of information used dishonestly or ignorantly to bolster an untenable, illogical view.

    2) You don’t need to know any atmospheric science at all. The basic problem is “The climate has always changed”. So what? What’s caused it to change? The second law of thermodynamics tells us it can’t change in its own. Tell me some mechanisms by which the climate might change. ? Solar output, yes, possible ? Orbital change, certainly. ?Volcanic eruption, yes ? change in the planets geography from continental drift – of course. ? cosmic rays or supernovae, possible ? asteroid impact, very likely. ? human impact – of course not????? Why not, human impact is an independent variable, There is literally no logic to say because A (global warming) can be caused by B, C, D or E, that an independent variable, G, human activity, cannot then cause the same effect. Is diabetes caused by overeating or poor diet? – yes Inheritance – ok? Obesity and or lack of exercise? – strongly implicated, autoimmune disorder? of course. So a doctor removes your pancreas, another independent variable, and that CAN’T cause diabetes whatever the evidence to the contrary ????? That’s plainly ridiculous -it’s a straightforward logical fallacy to suggest that as something caused by W, X or Y, that Z, independently, cannot, No science even needed.

  46. 96
    Paul Pukite says:

    “Ironically, it is far more likely that there are leprechauns than that there is some unknown yet to be discovered climate forcing.”

    The important caveat is unknown climate forcings, as yes, there are sources for forcing that are beginning to become more visible due to better time series resolution and more advanced analysis techniques. As both the geophysical labs at NASA JPL and Paris/SYRTE are recognizing, the lunisolar gravitational impact is emerging as a mechanism for atmospheric and oceanic flow patterns, such as ENSO. Moreover, groups at the USGS and at University of Tokyo are finding that lunar forcing correlates as a trigger for earthquakes, something that has been speculated on for years until landmark papers appeared last year.

    This is serious business because predicting El Ninos and earthquakes can save untold lives. Basing predictions off of the well-known orbital patterns of the earth/moon/sun system could make future predictions as straightforward as producing tidal tables. More here: http://contextEarth.com/2017/07/06/confirmation-bias/

    Watch this topic evolve as there will certainly be much contention in the coming years.

  47. 97
    Victor says:

    “Unlike a belief in leprechauns, there is a preponderance of evidence that CO2 warms the planet and that the anthropogenic contribution of CO2 to the atmosphere is causing the observed warming trend. Not only is there a preponderance of evidence, that evidence is quite compelling.”

    What evidence do you have in mind? What I keep seeing is evidence the Earth is now warmer than it was 150 years ago. There is plenty of evidence that this is so, and I’ve rarely read anything by any “denier” that argued otherwise. There is also evidence suggesting that warming beyond a certain point could be harmful or even extremely harmful. I see plenty of that sort of evidence, hyped on a daily basis by the mainstream media. I have my doubts on that score, but who knows?

    As far as evidence for CO2 emissions as a significant cause of the warming, sorry but I see precious little of that. Unless you consider the long list of what amount to excuses for the lack of correlation between CO2 levels and warming as evidence. Back in 2014, that list was already up to 66. (http://hockeyschtick.blogspot.com/2014/11/updated-list-of-64-excuses-for-18-26.html) And that covers only the “hiatus” since 1998. What about the even longer hiatus from 1940-1979?

    Is that what you call evidence? The introduction of one theory after another to account for the LACK of evidence? In flagrant violation of Occam’s Razor?

  48. 98
    t marvell says:

    VICTOR @23 – CO2 increases lead to temperature increases only after a lag, probably 20-30 years, due to feedback effects, mainly from the ocean. So your comparison of contemporaneous CO2 and temperature trends is not valid.

  49. 99

    KIA 94: There is no such thing as a “science denier”.

    BPL: Sure there is.

    KIA: You cannot deny that which you do not know

    BPL: But you can deny your own ignorant misconception of it.

    KIA: and almost no one understands the AGW science details (except climate scientists).

    BPL: No, anyone who tries to study the matter can pick up enough familiarity with it to understand what’s going on. The greenhouse effect isn’t all that hard to understand.

  50. 100

    Some recommended books for those who don’t want to become climate scientists, but want to pick up enough to be knowledgeable about the debate:

    George S. Philander 1998. Is the Temperature Rising?
    Spencer Weart 2008. The Discovery of Global Warming.
    P.J. Robinson and Ann Henderson-Sellers 1999. Contemporary Climatology.

    This one is a little harder (more math):

    Dennis Hartmann 1994. Global Physical Climatology.