Arguments
What does past climate change tell us about global warming?
What the science says...
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Basic
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Intermediate
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Greenhouse gasses, principally CO2, have controlled most ancient climate changes. This time around humans are the cause, mainly by our CO2 emissions. |
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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)
At a glance
Just imagine for a moment. You fancy having a picnic tomorrow, or you're a farmer needing a dry day to harvest a ripe crop. So naturally, you tune in for a weather-forecast. But what you get is:
“Here is the weather forecast. There will be weather today and tomorrow. Good morning.”
That's a fat lot of use, isn't it? The same applies to, “the climate's changed before”. It's a useless statement. Why? Because it omits details. It doesn't tell you what happened.
Climate has indeed changed in the past with various impacts depending on the speed and type of that change. Such results have included everything from slow changes to ecosystems over millions of years - through to sudden mass-extinctions. Rapid climate change, of the type we're causing through our enormous carbon dioxide emissions, falls into the very dangerous camp. That's because the faster the change, the harder it is for nature to cope. We are part of nature so if it goes down, it takes us with it.
So anyone who dismissively tells you, “the climate has always changed”, either does not know what they are talking about or they are deliberately trying to mislead you.
Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!
Further Details
Past changes in climate, for which hard evidence is preserved throughout the geological record, have had a number of drivers usually acting in combination. Plate tectonics and volcanism, perturbations in Earth's slow carbon cycle and cyclic changes in Earth's orbit have all played their part. The orbital changes, described by the Milankovitch Cycles, are sufficient to initiate the flips from glacials (when ice-sheets spread over much of Northern Europe and the North American continent) to interglacials (conditions like the past few thousand years) and back – but only with assistance from other climate feedbacks.
The key driver that forces the climate from Hothouse to Icehouse and back is instead the slow carbon cycle. The slow carbon cycle can be regarded as Earth's thermostat. It involves the movement of carbon between vast geological reservoirs and Earth's atmosphere. Reservoirs include the fossil fuels (coal/oil/gas) and limestone (made up of calcium carbonate). They can store the carbon safely over tens of millions of years or more. But such storage systems can be disturbed.
Carbon can be released from such geological reservoirs by a variety of processes. If rocks are uplifted to form mountain ranges, erosion occurs and the rocks are broken down. Metamorphism – changes inflicted on rocks due to high temperatures and pressures – causes some minerals to chemically break down. New minerals are formed but the carbon may be released. Plate tectonic movements are also associated with volcanism that releases carbon from deep inside Earth's mantle. Today it is estimated by the U.S. Geological Survey that the world's volcanoes release between 180 and 440 million tonnes of carbon dioxide per year - as opposed to the ~35 billion tonnes we release.
Epic carbon releases in the geological past
An extreme carbon-releasing mechanism can occur when magma invades a sedimentary basin containing extensive deposits of fossil fuels. Fortunately, this is an infrequent phenomenon. But it has nevertheless happened at times, including an episode 250 million years ago at the end of the Permian Period. In what is now known as Siberia, a vast volcanic plumbing-system became established, within a large sedimentary basin. Strata spanning hundreds of millions of years filled that basin, including many large coal, oil, gas and salt deposits. The copious rising magma encountered these deposits and quite literally cooked them (fig. 1).
Fig. 1: schematic cross section though just a part of the Siberian Traps Large Igneous Province, showing what science has determined was going on back then, at the end of the Permian Period.
Now laden with a heavy payload of gases, boiled out of the fossil fuel deposits, some of the magma carried on up to the surface to be erupted on a massive scale. The eruptions – volcanism on a scale Mankind has never witnessed - produced lavas that cover an area hundreds of kilometres across. Known as the Siberian Traps, because of the distinctive stepped landforms produced by the multiple flows, it has been calculated that the eruptions produced at least three million cubic kilometres of volcanic products. Just for a moment think of Mount St Helens and its cataclysmic May 1980 eruption, captured on film. How many cubic kilometres with that one? Less than ten.
Recently, geologists working in this part of Siberia have found and documented numerous masses of part-combusted coal entrapped in the lavas (Elkins-Tanton et al. 2020; fig. 2). In the same district are abundant mineral deposits formed in large pipes of shattered rock as the boiling waters and gases were driven upwards by the heat from the magma.
Fig. 2: an end-Permian smoking gun? One of countless masses of part-combusted coal enclosed by basalt of the Siberian Traps. Photo: Scott Simper, courtesy of Lindy Elkins-Tanton.
It has been calculated that as a consequence of the Siberian Traps eruptions, between ten trillion and one hundred trillion tons of carbon dioxide were released to the atmosphere over just a few tens of thousands of years. The estimated CO2 emission-rate ranges between 500 and 5000 billion tonnes per century. Pollution from the Siberian Traps eruptions caused rapid global warming and the greatest mass-extinction in the fossil record (Burgess et al, 2017). There are multiple lines of hard geological evidence to support that statement.
We simply break into those ancient carbon reservoirs via opencast or underground mines and oil/gas wells. Through such infrastructure, the ancient carbon is extracted and burned. At what rate? Our current carbon dioxide emissions are not dissimilar to the estimated range for the Siberian Traps eruptions, at more than 3,000 billion tons per century. The warning could not be more clear. Those telling you the climate's changed before are omitting the critical bit – the details. And when you look at the details, it's not always a pretty sight.
Last updated on 14 February 2023 by John Mason. View Archives
Scott0119,
You asked, "if we completely eliminate human CO2 emissions we could send ourselves into another ice age? Or am I oversimplifying the issue?"
According to this paper published in Nature: Evolution of global temperature over the past two million years , judging by the fossil record it appears as if we are locked into continued warming for a while at least even if we stopped all fossil fuel use tomorrow. Earth 'Locked Into' Temperatures Not Seen in 2 Million Years (all else equal of course).
However, all else need not be equal. Humans being a tool using species have the ability to do great works of ecosystem healing just as easily as we can do great works of destruction. In this case it means we have the knowledge tools and capability to sequester rapidly in the agricultural soils of the world more than enough carbon to "unlock" that "locked in" scenario.
Simply eliminating fossil fuels completely won't stop AGW. We waited too late for that. Sequestering carbon in our agricultural soils world wide by itself is probably too late for that too. But doing both ? That actually can finally reverse AGW, and such draconian measures need not be necessary. We could still burn a little fossil fuels and still have some ag that isn't carbon farming. In other words if we approach this from all angles we can drop it in as a replacement to all our unsustainable systems where economically feasable and the problem would vanish...and at a net economic profit!
I have written a rough outline essay how that might work here: Can we reverse global warming?
Here is a description of both the challenges and solutions we are facing in US: Can American soil be brought back to life?
Here is the same basic concept as developed in Australia: FARMING A
CLIMATE CHANGE SOLUTION
and
Why pasture cropping is such a Big Deal
And here is the Chinese efforts and early results for the same concept:
“Grain for Green” driven land use change and carbon sequestration on the Loess Plateau, China
Executive summary:
Yes we can reverse Global Warming.
It does not require huge tax increases or expensive untested risky technologies.
It will require a three pronged approach worldwide.
Either way though, a glaciation event is not in any forseeable future. Quite the opposite problem.
First, please note that I'm a skeptic of AGW theories. I believe that at best, Mankind may have the capacity induce a relatively minor impact relative to the sources of natural variation.
Holocene is considered an Ice Age with the last Glaciation endingn ~11K to 12k years ago. I don't know the catalyst that shifts from an 'Ice Age' to a 'Warm House'. (Need to research that) We do know it has happened many times before our arrival.
Looking at temprature records of the 12 Periods in the current Era, 84.7% of the time the Globe was several degrees warmer. It seems logical to assume the planet tends to gravitate to that level with ouside events triggering major cooling events.
Consider:
84.7% of the Phanerozoic Eon was on average ~3+ degrees warmer than current.
Holocene is considered an Ice Age. (Something cooled things off, but the planet is trying to return to its 'normal' balance which is closer to that 84.7% of the time level.)
Is it possible the current Ice Age has ended due to some factor we have not yet considered?
What I am really asking is; How many global climate factors are there that we have we do not yet fully understand? How big could their impacts be? What is the likelyhood that there are significant factors that we do not yet understand and or have not discovered.
I'm an AGW skeptic because I find it difficult to accecpt that only 0.03% of the atmosphere is responsible for controlling changes in Global Climate.
Statistically speaking: 0.0003 could be viewed as a rounding error. (This point is for dramatic effect only)
The planet is warming. On this we all agree.
[TD] The percent of the total atmosphere that is CO2 is irrelevant. The only gases that are relevant are greenhouse gases, of which CO2 is one. With regard to forcings, there are even fewer relevant gases; water vapor condenses so it is a feedback, not a forcing. So a relevant percentage is the percent of all non-condensing greenhouse gases that is CO2.
There is overwhelming, concrete, empirical evidence for an increase in CO2 causing warming.
Human activities' contributions of CO2 to the atmosphere are not balanced by human activities' removals of CO2 from the atmosphere. In contrast, the natural contributions and removals closely balance. CO2 is removed from the atmosphere by natural processes very slowly, so human contributions accumulate.
[PS] Please note that Sks organizes arguments into different topics. Please do not make offtopic comments. Use the search button on the top left to find relevant topics and comment there after you have read the article. Repetition of long-debunked arguments is boring.
jop3v2 @577,
Concerning your self-description "I'm an AGW skeptic because I find it difficult to accecpt that only 0.03% of the atmosphere is responsible for controlling changes in Global Climate." Consider the following analogy:-
I live in a house that I estimate contains about 60 tons of material in the walls (333mm x 3m x 10m x 4walls with sg =1.5). The atmosphere contains today 400ppm by volume and 610ppm by weight of CO2, or 0.06%. Studies suggest that if CO2 were entirely removed from the atmosphere, the greenhouse effect would effectively disappear and global average temperatures would fall 33ºC. There are a lot of things that result from the removal of atmospheric CO2 (as described in the linked SkS article) so the analogy with my house is not exact. Also note the planet's troposphere contains a 75ºC temperature drop while the inside/outside temperature difference across the walls of my house is no more than 20ºC, even in winter. So consider if I take the front door off my house in mid-winter. There will be a dramatic change in the room temperature, very likely reducing the average inside/outside temperature difference by more than 50%. If the front door weighs 36kg, it would constitute 600ppm by weight of the house. (It probably weighs a lot less.)
jop3v2 says "The planet is warming. On this we all agree."
Actually, no. I have been around the mind manipulation wars on climate for a good number of years. There are countless fake skeptics who in fact disagree with that and have made a living of attempting to spread doubt about that very point. Most famously, Anthony Watts, who was proven wrong in his assumptions very early on by an amateur going by the handle of John V. He was proven wrong again later by NOAA and finally by his own publication. It was a fairly inconsequential paper, that still took him years to produce; it did not lead him to disavow his years of accusations of fraud against others, encouraging his readers to harass scientists by putting their personal addresses on his site, or putting up posts so grotesque that only the scientificaly illiterate could take him seriously (Antarctica carbonic snow comes to mind). And he is only one of many; some are in the highest positions of power. Your concluding statement is verifiably wrong. Perhaps you should have said: "we, people amenable to reason, all agree with that." I would concur if phrased that way.
Another part of your argument to which I object is the "humans too small to affect anything." It is common and sometimes comes from people who are religious minded. However, it is not valid either. Imagine all the carbon dioxide released from volcanic activity happening naturally on Earth over a year. Now, multiply that by approximately 100 (give or take); that's how much we have been and are still releasing, year after year. Any argument that this does not constitute a geological scale event is wrong, purely from simple quantitative considerations. Geological scale events have geological scale ramifications.
The per volume fraction of CO2 is seemingly small, but that does not change the physics. If CO2 was not transparent to visible light and we could actually see its increase just by looking at photos of now vs 35 years ago, we certainly would be more enclined to take the threat seriously, because that's the kind of animal we humans are. We also are very bad at anything truly long term, although this has become far worse in the recent past, under the pressure of an extreme ideology of maximizing short term gains at any cost, present or future.
There is more to discuss about the fact that we weren't around as a global civilization in the time periods you mentioned and that we developped as such in a certain range of conditions; we then built some pretty heavy infrastructure that is already compromised by rapid seal level increase. We established industrial agricultural practices that, for all their machinery and chemical underpinnings, are nonetheless most dependent on rainfall, seasonal cycles, and low probability of extreme events. The rapidity of the change we are witnessing now is far more relevant to us than the actual position of equilibrium in a past when we were just tagging along with all the other critters.
[PS] can I ask all responders to jopv32 to reply on an appropriate thread? You can place a pointer to your reply here.
In a relatively recent study by Kemp, Eichenseer and Kiessling, the authors argue that the change in climate may have been faster (maybe as fast as now) before, but this can't be seen in the data, since most data only refers to long time intervals.
(https://www.nature.com/articles/ncomms9890)
Is there a response to that? What is your opinion on that study?
Abrupt global warming in the Permian and Triassic periods were associated with higher CO2 levels. Climatologists speculate on the reasons for the sudden increase in CO2 levels, but obviously during those time periods the increase was not human induced. This fact is a crucial and painful one for the "consensus" who argue that our current (slight global warming) trend is man made. To assume an unknown (the imprint of human activity on our climate) over a known (Historical data proving our climate has changed with increases and decreases in CO2) is a lazy stance for scientists to take.
[PS] Please provide a citation to support your statement "To assume an unknown (the imprint of human activity on our climate) over a known (Historical data proving our climate has changed with increases and decreases in CO2) ".
ie show us where science has made that assumption rather than deducing it from known and testable physics.
Cero,
I read the article you cite. I noticed that they first claim that it is not possible to measure the rate of climate change in the distant past because of inherent problems with the samples. Then they claim to adjust measured data to correct for these random changes. That is a contradiction to their first claim.
They have only been cited 4 times by other scientists. It appears that other scientists think the paper is not very valuable. It appears that deniers cite this article.
Rodhole,
Since people died before guns were invented, according to your logic guns cannot kill people. If the CO2 concentration increase is not caused by humans, where is all the CO2 we release into the atmosphere going? A simple measurement shows that the increase in CO2 concentratio only accounts for half the CO2 we have emitted. The rest dissolved into the ocean. In order for your claim that the increase is natural to be true you must show where the CO2 we emitted went and where the CO2 icrease in the atmosphere sent.
In addition, there are chemical means to show the increase in CO2 is human caused and not natural.
Deniers are so lazy they cannot even be bothered to do addition and subtraction.
Sweet,
No, guns actually CANNOT kill people. Guns are man made and need a conscious handler in order for them to activate. But I would assume then that you would argue that because people have used guns to kill others, the real problem lies with the gun manufacturers? I guess it would depend on the amount of emissions released during the making of a gun to guide your opinion.
My point is not that emissions caused by humans is irrelevant. I think it is something that we should be responsible with (without losing our minds and/or implementing stupid laws that hurt our economy). My point is that it is arrogant to believe that after millions of years of climate change, certain scientists insist that "this one" is bc of humans.
Whether these scientists truly believe the human race was not meant to live on this earth (bottom line of debate), they fear being an outcast in the science community (reality), or they are getting incentivized to postulate an agenda (my assertion), the latter 2 of the 3 is wrong.
[DB] Welcome to Skeptical Science. First, the ground rules for this venue are found in this site's Comments Policy. Read them. Learn them. Construct future comments to comport with them. Attempting to score meaningless rhetorical tricks employing logical fallacies that also show a large ignorance of the science in question in specific and the scientific method in general, as you do here, reflect poorly upon you and damage your credibility in this venue.
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Multiple inflammatory, sloganeering and ideological talking points and logical fallacies snipped.
Skeptical Science,
Being new, I was not aware of the rigorous monitoring of the rules. Regardless, that was a perfectly fine rhetort to the post "attacking" my assertions. Am I not allowed to defend my comments? Why didn't you strike her initial comment on guns? Do you just outlaw things (especially if it makes your cohorts look bad) that you don't agree with?
One thing I learned in college is to have an open mind and allow others to voice their opinion. Unfortunately these days opinions that don't comform with the "consensus" are dismissed. I hope this cite does not only allow things it agrees with. If it does, than this not a place for thoughtful discussion, rather it is a place of pretend fantasyland.
BTW, I didn't know what it meant so I had to look up "sloganeering". I laughed bc this entire comment section is "sloganeering".
[DB] FYI, the Comments Policy applies equally, to all.
Please note that posting comments here at SkS is a privilege, not a right. This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.
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Funny that you didn't publicly post the rest of what I said? I get it, you are scared of intellectual confrontation. This will be my last post on this fake cite.
When you go to sleep tonight, think about how dishonest this cite is. You are so frightened by differing opinions (which happen to be based on science and data) that may make you wrong, you choose to cut those people off rather than let them speak. It is a common liberal playcall, so I am not surprised.
I'll let you continue your shameful dominance over the realm of scared dorks who dont want to break a rule, while I continue to have open and honest conversations with people. From my experience in talking with people over the last 20 years, the farse of "man made global warming" is declining by the day. Al Gore's bank account is not happy I'm sure.
[DB] I'm sorry, that your position is so weak that you are unable to bring any actual evidence for your position to this, an evidence-based site. I'm further sorry, that you feel compelled (like a moth to a flame) to repeatedly violate a code of conduct that well over 99% of participants here routinely adhere to with no difficulties whatsoever.
As for your remaining comment, even Exxon affirms the unassailable evidence, consensus, facts and the alarmist "farse" of AGW:
Rodhole @586 , I am sure that genuine intellectual "confrontation" (from you?) would be welcomed, if you care to accompany it with some well-reasoned factual basis. But this site [please note correct spelling] is very uninterested in receiving moronic confrontation even without multiple spelling errors and factual errors, which you exhibit. Nevertheless, I acknowledge and bow to your immense superiority.
Moderators — as always, please feel free to delete my post, if you feel the pruning shears are called for, in this thread!
[DB] Inflammatory snipped. As you note, all who bring credible evidence for their position and comport themselves with the Comments Policy are welcome here.
Rodhole has recused himself from further participation in this venue.
@michael sweet:
I don't think, they claim, that it is not possible at all to measure the rate of climate change in the distant past, but they claim that the conclusions from the data are much less accurate than is commonly believed. Therefore it makes sense to correct for that.
They only have been cited 4 times, however the article is only two years old. And maybe they just didn't get that much attention. Still, the article was published in a well-known peer-reviewed journal.
That climate change deniers cite this paper can't be an argument against its validity.
cero @580,
I can see Kemp et al (2015) being drooled over by denialists. This would be because they misinterpret the paper which sadly misses out on saying explicitly things that are obvious in any genuine reading of the paper.
The idea that ancient warming episodes may have contained more rapid events within the actual warming, that the average rate of warming will inevitably be exceeded over shorter sections of that warming: this is logical. And when you are concerned how quickly, say, an oak forest habitat can shift polewards, those speedier intervals are relevant.
As Michael Sweet points out, we cannot (yet) measure such short accelerations from the available data so Kemp et al set out a new method to infer those increased levels. This is interesting stuff, and very early days, so it cannot be seen as entirely reliable. Consider the PETM which we know took millennia to occur. It was a gentle warming over a long period and would have had periods of increased and decreased rates of warming. Thus Kemp et al take central estimates for this event (5ºC to 9ºC = 7ºC, ~5ky to 20ky = 12.5 ky, this a rate of warming of 0.0006ºC/yr compared with recent rates of 0.015ºC/yr ) and adjust these to suggests a potential millennial rate of 0.0032ºC/yr or about half the PETM warming occurring in a single millennuim.
Other measured temperature rises are likewise adjusted. A 15ºC measured ocean warming over 800,000 years during the P-T (250My bp) is inferred to include a millennial period of at least 4.5ºC warming. (Potentially we could deduce a 9ºC warming over 2,000 years.) Or the Bølling-Allerød during the warming from the LGM (13,000yr bp) measured at 3ºC over 100 years is adjusted to equate to 2.2ºC over a millennia.
So I am on safe ground when I suggest that Kemp et al have not begin to capture the scale of that adjustment. They have set out a method that begins consideration of it.
But there is a missing aspect within the paper if it to be used to argue about the rate of AGW relative to previous non-anthropogenic warming. We are facing a temperature rise of 4ºC in a little over 100 years from unmitigated AGW. Such a rise would rival the magnitude of the largest millennial warming set out by Kemp et al. The caution Kemp et al say "must be exercised when describing recent temperature changes as unprecedented in the context of geological rates" does not apply to expected future unmitigated temperature changes.
Answer is: whether it's going too fast or not!
(Did I win?)
Thanks @MA Rodger. That was the kind of explanation I was searching for. :-)
Recommneded supplemental reading:
The climate has changed before. But this is different – look at the archeological record by Peter B Campbell, Guardian, Nov 9, 2017
The Campbell article John Hartz mentioned is well-written but doesn't present a lot of historical or archaeological evidence, and the conclusions to me seem understated.
According to SkS's database this, 'Climate's changed before' is by a slight margin the most popular 'argument' used to protect against 'alarmism' (or action, whichever way you see it).
In the taxonomy, it's listed as a subead of 'It's not us', and this is the usual implication of 'no one denies the climate changes' by committed contrarians - they may go on to assert there's some (unknown) mechanism causing the current rapid warming instead of the predicted enhanced greenhouse effect.
However I would like to suggest that the conclusion reached from 'climate always changes' by most people fits more under the 'It's not bad' top-level heading. howardlee's 'rebuttals' address to an extent by talking about rate of change and past impacts, which are factual points. 'It's not bad' is not purely factual, because 'bad' is a value.
What I mean is that people will use weather, weather ranges, historical climate variations, glacial cycles over human development, or geological records back to the Precambrian to assure themselves, in combination with the self-evident fact that 'we are here', that civilisation, human life or life itself is more 'resilient' than fragile to substantial temperature or CO₂ changes. If it's happened before then it can't be too bad and is not worth regretting. Again, this stance is as much based on values as facts, as described in Mike Hulme's Why We Disagree About Climate Change. Possibly individualists think nature is less unstable than do egalitarians, although that link wasn't immediately obvious to me.
You can also see a ethical evaluation being superimposed in data when discussing 'dangerous' thresholds, for example J. Hansen et al.: Ice melt, sea level rise and superstorms. What are the dangers? Although these are detailed in the IPCC WG2 reports, in some ways it's sketchy precisely because these are unprecendented changes or rates of changes. Very few think a runaway effect that destroys all life on Earth is likely, so anything less is a kind of survival, and it's possible to 'concertina' geological time with possible changes in frequency recent extreme weather events without fully appreciating what a mass extinction means. A few metres of sea-level rise has happened before, and if it happens over 200 years then it isn't the end of the world.
Largely I think these are still tacit positions when people seem to be discussing topical issues, but they are things on which scientific research and reason can be brought to bear. We can make partial projections based on past evidence of harms and benefits, such as at the Royal Society meeting on hyperthermals. But the possibility of unexpected dangers are harder to evaluate, and most people may assume the existence or otherwise of precedents is the only way to decide whether climate change is a bigger environmental problem than habitat fragmentation or plastic pollution, or how the amount of human endeavour to mitigate it necessary for long-term survival compares to that put into education or defence. Integrated Assessment Models are not the only way one can form an opinion on what the carbon price should be. 'Lukewarmers' presumably hold these kinds of thoughts along with a historical knowledge of previous millennialism and mass hysteria to evaluate the current situation, while others passively dismiss climate concern using similar reasoning.
So there may be several related deeper objections or questions where SkS can summarise evidence. These may often underlie the search for, or adherence to, pseudo-scientific arguments used by contrarians. I may post again on what these are specifically.
Cedders @ 594
As one who is clearly a "lukewarmer", at least, I will look forward to any further posts you have while I personally try to get a handle on issues relating to the measurement of sea levels and actual measurements of global temperature rise.
My underlying concern remains that that the climate system is so complex that the models cannot adequately predict what is going to happen (yes I know this is the topic of another thread). It does not mean it is not going to happen but to ask the world to shift its FF use over a very short time frame is a hard sell. Perhaps you can deal with this in your suggestions to SKS. Another suggestion I have made to SKS (which seems to have fallen on deaf ears) is to address the alternatives and their cost to assure the Republicans in the US (which is surely what has to be done) that there is a reasonable alternative. I understand that this website is not dedicated to those issues but, in my view, those are so critical to convincing the public that they have to be addressed in one or more formal threads dedicated to same.
[DB] Off-topic snipped.
"First, to infer that humans can't be behind today's climate change because climate changed before humans is bad reasoning (a non-sequitur)."
Nobody suggested this, not even in your quote. We're just saying that the whole concept of climate change being a problem is ridiculous. Because the climate always changes, by definition. Too fast climate change might be a problem. Humans breath out CO2 and breath in Oxygen, of course we affect our environment. Nobody disputes that. Please stop with the straw-men arguments. We're just saying that there's no reason to assume change is necessarily bad. We have to do actual science instead of fear mongering.
"Second, to imply we have nothing to fear from today's climate change is not borne out by the lessons from rapid climate changes in Earth's past."
When archeologists say 'rapid', they mean thousands to hundreds of thousands of years. When the collection of species in an ecosystem changes it sounds really bad. Suggesting that all the animals normally just live their happy lives, but with such a change they all suddenly die. This is not how reality works. Animals struggle to live their most of their life. An environmental change that causes the species to change just means some species become a little less successful at that every year and some a little more. So an individual animal probably won't notice the difference.
[PS] "We're just saying that there's no reason to assume change is necessarily bad. We have to do actual science instead of fear mongering." Yes, lets indeed to the science. You can find that science summarized nicely in WG2. You will also find the scientific answers to of many of the myths about rapid change here under the section "Its not bad". Your concluding statement is sloganeering, because you are making assertions without providing supporting evidence in the face of established science.
As this is your first post, Skeptical Science respectfully reminds you to please follow our comments policy. Thank You!
Before humans have existed, the big climate changed has happened before and it leads to cause major extinctions naturally. Scientists believe that, over time, changes in the amount of CO2 in the atmosphere have altered the climate of the planet. The proportion of CO2 that is dissolved in the ocean, as opposed to the CO2 that is present in the atmosphere, also varies over time. When more CO2 is trapped in the oceans, the planet cools. By contrast, when atmospheric levels are high, the planet warms. Carbon dioxide is considered to be the most important greenhouse gas involved in global warming. (from http://www.arctic.uoguelph.ca/cpe/environments/climate/climate_past/ice_cause.htm)
So after humans have existed, people are putting CO2 more and more into the atmosphere. But cause minor extinctions because climate changes cause major extinctions from cooling not warming.
If humans are not the factor that causes big climate changes and let the world run naturally, will the next major climate changes be like ice age?
Bearling, where do you get the idea that mass extinctions are caused by cooling not warming? That doesnt match the published science. The critical thing affecting extinctions is rate of change (because organisms need time to adapt/migrate) not the direction of the swing. Also the Pliestocene ice age cycle is rather slow and not notably associated with extinctions (except where low sea level allowed humans to migrate into new areas where they wiped out the local megafauna), unlike the current rate of change caused largely by our emissions.
If humans werent around then next peak age would be about 80,000 years. There is more info on this here.
Rates of change is always the concern. The global debate should be about this but it's not because business has already accepted the reality of climate change: everything else is the vagaries of investment.