This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
The current warming is just part of a natural cycle.
While it is undoubtably true that there are some cycles and natural variations in global climate, anyone who wishes to insist that the current warming is purely natural or even just mostly natural has two challenges. Firstly, they need to identify just what the mechanism is behind this alleged natural cycle, because absent a forcing of some sort, there will be no change in global energy balance. So natural or otherwise, we should be able to find this mysterious cause. Secondly, a "natural cause" proponent needs to come up with some explanation for how a 35% increase in the second most important greenhouse gas does not itself affect the global temperature. Theory predicts that the temperature will rise given an enhanced greenhouse effect, how is it possible this is not happening?
In other words, the mainstream climate science community has provided a well developed, internally consistent theory that predicts the effects we are observing. It provides explanations and makes predictions. Where is the sceptic community's model, or theory whereby CO2 does not affect the temperature? Where is the evidence of some other natural forcing, like the Milankovich cycles that controlled the ice ages, a fine historical example of a very dramatic and very regular climate cycle that can be read in the ice core records taken both in Greenland and in the Antarctic?
Is this a candidate for today's warming? A naive reading of this cycle indicates we should be experiencing a cooling trend now, and indeed we were very gradually cooling over the length of the pre-industrial Holocene, something around .5C averaged over 8000 years. Not only is the direction of the change wrong, but it is informative to compare the speed of those fluctuations to today's changes. Leaving aside the descents into glaciation, which were much more gradual, the very sudden (geologically speaking) jumps up in temperature every ~100Kyrs actually represent a rate of change roughly ten times slower than the rate we are currently witnessing.
So could the current change be natural? Well, there is no identified natural cause (and they have been looked for), there is no theory of climate in which CO2 does not drive the temperature and the natural cycle precedents do not show the same extreme reaction we are now witnessing.
(That would be a "No")
This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
"This is Just a Natural Cycle" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.
Have you seen the newly published material on the Pacific Decadal Oscillation?
exec type summary here:
more info here:
thank you - I enjoy your site and respect that you allow such spirited debate.
Interesting stuff, thanks. I have come across discussion of the PDO/AMO cycles before but did not delve into it too much as of yet.
I assume that the conclusion that is at least being implied is these cycles can explain 20th century warming, which I am not sure is justified based on correlations alone. Undoubtedly ocean currents influence regional and local climates but it is hard to see how they could cause any NET changes in the energy balance in the climate system as a whole. The other challenge this hypothesis faces is finding a reason for these currents to be changing. Perhaps this was in the material you linked, I was not able to give it the full time it deserved.
Thanks for the comment!
I don't like how this is written for two reasons:
1) You assume human intervention is the rule and require others to prove otherwise (example: they need to identify just what the mechanism is behind this alleged natural cycle. My understanding is that we cannot explain 100% of the cycles in history. Why would "not explaining this cycle" undoubdtedly lead us to conclude that the cause of the change is human?)
2) I am surprised (not really) that you did not mention the small detail that historically, temperature changes have led CO2 changes. In other words, I think evidence that temperature causes CO2 changes is stronger than the evidence that CO2 changes lead to temperature changes.
Honestly, in the end, we can't just say: well, you have to prove me wrong. Our ignorance about climate changes (and we all know we are pretty ignorant about climate issues (for example, what is our lead time in predicting tornadoes?) is fairly well known. Ignorance of the climate is not enough evidence that humans must be causing global warming.
I am not saying humans did not cause global warming. I just don't think the evidence is unequivocal.
Re "1)" - I don't assume anything, rather copious amounts of evidence lead me to that conclusion. In the presence of a strong, working hypothesis an appeal to some undetected, unidentified "natural" (or not) cause is hardly compelling.
Re "2)" - the two processes are not mutually exclusive, accumulating CO2 causes warming, warming causing CO2 accumulating CO2. Check this article on how CO2 lags warming.
Your last bit confuses weather and climate and exagerates science's ignorance on this topic. There is much we don't understand, but the greenhouse effect is very well established and the importance of CO2's role tightly contstrained both by theory and observations.
Thanks for the comment!
That article about CO2 lags warming proves my point. There is no conclusive evidence that human activity "caused" or "led" to global warming.
I posted the following issue in the other one too...
Let's talk about your hypothesis: You can only statistically "reject" a null hypothesis. The only testable hypothesis is that humans caused global warming. The best case scenario for people that believe humans caused global warming is to "fail to reject" the null hypothesis. This does not mean (based on your background, I assume you know this) that we have proved that humans did cause global warming. It just means that it is possible that humans caused global warming - which is what I am asserting.
"The two processes are not mutually exclusive, accumulating CO2 causes warming, warming causing CO2 accumulating CO2."
Wouldn't that lead to a positive feedback system? And wouldn't that mean an exponential trend? I've never seen anything that suggests temperate changes occur exponentially.
Yes positive feedback, no exponential trend. Feedbacks do not have to be "runaway", they can be self limiting. In the climate system there are two mitigating aspects. First, sources of CO2, they are not unlimited. Second is CO2's logarithmic influence on temperature. As CO2/temperatures rise, it takes more and more CO2 each additional degree. Best estimates of climate sensitivity to CO2 is ~3oC per doubling.
Should also mention that the 3oC figure does not include carbon cycle feedbacks (the temp causes CO2 aspect)
Have you spent more time with the PDO/AMO cycles or found any good sources? I read an unpublished article citing "Wilson (2008)" to the effect that PDO effects have been positive since the 1970s and have recently turned negative - coinciding with the last few years' cooling trends. The (Wilson) graphs shown still suggest a positive trend since 1880 with smaller down legs and larger up legs though with just 4 changes it would be hard to extrapolate to any conclusion as to whether PDOs are an alternate explanation to GHGs...
Some info on the PDO
'Firstly, they need to identify just what the mechanism is behind this alleged natural cycle,"
Sun spots. Just ask NASA. To go even further I actually learned about this in Earth and Space class in grade 12 in high school. Ice ages are caused by sun spot activity.
Thank you for your time.
I need some help, as I'm just a simple retired science teacher. I've read a couple of these blogs now, and I'd really like someone to direct me to information that is actually based on some experimental science which replicates atmospheric conditions at various incremental levels of CO2, and tries to quantify any warming effect. Computer modelling, just like any scientific hypothesis, is based on assumptions. I always taught my students that a good scientific hypothesis made as few assumptions as possible. It should also predict consequences that can be tested by experiment. Where are the experiments? The classic example of a scientific hypothesis based an ever increasing and complicated assumptions is the geocentric model of the universe. That great 'model of the universe' skeptic Galileo certainly held a minority view and was 'ostracised' for it by the inquisition and the prevailing "scientific correctness".
Wombat - I cannot imagine there could be such an experiment. The difficulties of setting it up are too huge. You would need a planet sized experiment!
As I understand it the physics of the hypothesis have been the subject of many experiments and the conclusions reached by those have been combined and factored into the various computer models. These models are then necessarily "tweaked" mathematically or added to as new information comes in so that at least they replicate the past and then we wait and see if they will predict the future. The first models, for instance,predicted quite a direct correlation between temperature and C02 content of the atmos and so failed to predict the recent apparent flattening , although I understand that present models can account for variations seen in the rate of increase.
Doubtless someone will set me straight if I have this wrong. I appreciate it is a profoundly simplistic exposition but I hope I have the basics more or less right.
Galileo. The most abused name in scientific history. He was ostracised *not* for holding a minority opinion, but for presenting that opinion in a way that was considered insulting to the pope. Of course, it is also rather odd to compare the current issue with that when the prevailing scientific opinion was tested against a religious book, and not so much against observations...
wombat, I highly recommend reading through Spencer Weart's History of Global warming. All the significant papers are covered, going back over a hundred years. Depending what you are looking for wrt experimental replications of atmospheric conditions, you will find the relevant research in there:
The first models, for instance,predicted quite a direct correlation between temperature and C02 content of the atmos and so failed to predict the recent apparent flattening , although I understand that present models can account for variations seen in the rate of increase.
The projections of the future we typically see are actually averages of ensemble runs and as such can not really be compared to the single instance of reality we experience. Individual model runs often show periods of up to ten years with no warming or slight cooling, this is simply the reality of a slow trend (.2oC/decade) superimposed on large natural variability (sometimes .2oC+ annually).
The GCM's relied on by the IPCC are not designed to predict short term changes, though of course researchers are trying to improve this kind of capability.
I think that desire is reflected in one of the CRU email soundbites goig around ("it is a travesty that we can't account for the recent temperature stasis", or whatever Jones said)
It's a travesty we can't account for the recent lack of warming. Kevin Trenberth, not Jones.
Marco, I used the example of Galileo, not to illustrate that his observations were tested against a religious book (or Pope Urban VIII's erroneous 'interpretation' of a religious book), but to illustrate experimental evidence used to support a minority view (the heliocentric model of the universe of Copernicus, Galileo and Kepler) against the prevailing and entrenched majority geocentric view of the Ptolemaic model, which was complex and needed to make many assumptions to satisfactorily explain it. The comparison is not unlike the current state of play with Climate Change science.
Wombat, what rational alternative explanation is there for the recent warming?.
@Wombat: I know why you used Galileo. Unfortunately for you, the issue wasn't geocentric vs heliocentric from a *scientific* point of view, but from a *religious* point of view.
The comparison is very much unlike the current state in climate change science: the alternatives that are offered simply do not stand up to the body of observations.
The issue was heliocentric vs geocentric from an evidence-based point of view. It's just that the evidence accumulated by Copernicus, Galileo and Kepler was better,and more accurately interpreted. The geocentric model of Ptolemy was based on evidence (incorrectly interpreted) and meshed with philosophy. The "church" was not around in 6th - 4th century BC, when these ideas first arose. My original assertion was that any half decent hypothesis must be based on sound experimental evidence. That's why I asked for citations for real experiments, not computer modelling, that replicates he warming or otherwise of our atmosphere at CO2 concentrations of 350 ppm and 450 ppm. Surely this is experimentally demonstrable.
"That's why I asked for citations for real experiments, not computer modelling, that replicates he warming or otherwise of our atmosphere at CO2 concentrations of 350 ppm and 450 ppm this is experimentally demonstrable." - Wombat.
Aside from the creation of Earth like planets and time machines to observe said experiments, what exactly do you have in mind?.
Some small scale controlled experiments that replicated the composition of the atmosphere at current and elevated [ CO2 ] under a constant incident light / heat source equivalent to the effect of the sun whould appear to be replicable. Where are the citations to them?
The computer modelling seems to be very complex and based on a great number of assumptions, yet great faith seems to be placed in them.
Any physical simulation would have bigger limitations than a computer model. Only certain effects could be taken into account - for example it would be difficult to physically reproduce orbital variations, changes to planetary tilt, ocean currents, volcanos, etc, etc.
It is more likely that a computer model could consider a greater range of effects. And the way to "prove" the computer model is to see how well it predicts what happened in the past.
The computer modelling (sic) seems to be very complex and based on a great number of assumptions, yet great faith seems to be placed in them.
You see, that is the difference between some one who has worked in an area of science for a long time and fully understands their field and a denier troll who wanders through scientific discussions with a complete lack of knowledge about what he decries and demeans with his ignorant comments.
Ooops my comment was to WanderingWhy not Wombat, my apologies.
Ian, you had it right first time, Wombat is the one guilty of denial.
I'm kind of puzzled why your correction cites me. Wombat seems to be the more logical recepient.
Although I do like Wombat's idea of a controlled experiement. We'd need a very large ball of rock - planet sized, 70% covered with water, some continents drifting about, atmosphere, parked about 150mill KM from the Sun, etc, etc. Would be good if it was covered in a variety of life forms. And we'll need some method to add/remove large quantities of CO2 from it's atmosphere.
Better check if the folk from Magrathea are awake yet!
Dappledwater, WanderingWhy et al,
Why a planet-sized experiment? I ask a serious question, and ask to be directed to experiments that have (or have not?) been done, not computer modeling, and no-one who has responded can direct me to any, I just get labelled as a climate change denier, which I am not. I am definitely suspicious, though, of computer models that are based on a large number of complicated assumptions, rather than some hard experimental evidence that shows there is a warming effect when CO2 levels are doubled from 350 ppm etc.
Dappledwater, you have a tendency to bag anyone who does not bow down to your superior knowledge. The sad thing about many of these forums (fora?) is that people on both sides of the debate have a tendency to degenerate to name-calling, rather than respecting each other and trying to engage in intelligent dialogue and inquiry. I only asked to be convinced, not harangued.
Wombat: you're mixing apples and oranges. The "apple" is experimental proof that CO2 doubling causes xÂ° rise in temperature globally. As others has posted, this cannot be done. Hence the building up of a huge database and body of evidence of past CO2 and temperature to develop mathematical models of the relationship. It is the clear correlation of higher CO2 with higher temperature that scares the cr-p out of those of us who do not see humanity responding to the clear need to reduce CO2 emissions in order to avoid long term serious impacts, if not a global extinction event. (And by "long term" I mean really short in geologic time, like a couple centuries.)
The "orange" is experimental proof that CO2 does in fact cause temperatures to rise. This is demonstrably a fact. Do the research: "greenhouse effect" will do it for you. The theory is almost 200 years old (1824) and was physically demonstrated in the lab shortly thereafter (1858)--solar radiation passing through CO2 and other "greenhouse gasses" gives up some of its heat to the gas instead of radiating back into space. If not for the greenhouse effect, Earth would be a fozen snowball. Swede Svante Arrhenius (1859-1927) actually made CO2:temperature predictions in 1896 that are remarkably consistent with today's sophisticated models; he was just off by a few centuries because he did not foresee the frenzied pace of human economic activity and related CO2 emissions through the Twentieth Century.
By the way, I'm not a scientist, just someone who tries to think critically. You might try it some time.
"I ask a serious question, and ask to be directed to experiments that have (or have not?) been done, not computer modeling, and no-one who has responded can direct me to any, I just get labelled as a climate change denier, which I am not."
Um, excuse me, but about two weeks ago I pointed you, without any name calling, to an excellent resource with just what you are asking for and you did not even mention it since then.
Have you looked at the train of scientific papers outlined by Spencer Weart's History of Global Warming? What is missing for you?
If I knew nothing of the whole debate on this issue, then I could easily assume (according to the graph) that rising temperature causes rising CO2 levels.
Suppose we start with the assumption that rising temps cause rising CO2 levels. Now let's create an intricate dogma around that premise, so the AGW slant will be the sceptics' side.
It would be an interesting exercise in marketing if nothing else.
I find it strange that we have such little data on the Southern hemisphere when we are talking about "global" warming. Currently it seems that the southern hemisphere is cooling markedly; the lack of extensive data points is a real problem...projections from scanty sites is not convincing.
As to proving why the warming is not anthropogenic...can you prove that earlier cycles were NOT natural?
"....Currently it seems that the southern hemisphere is cooling markedly...."
I assume you have some evidence for this? If so, please produce it.
It is not expected nor even plausible that all climate changes have the same cause, so what in the world is the purpose of challenging anyone to prove past cycles were not natural?
As for our fisrt paragraph, in one breath you assert there is insufficient data to claim warming and you then claim cooling. Very inconsistent...
JIMB is an obvious troll. Everyone can check the hemispheric data from GISS, HADCRU, RSS, or UAH, and find his claims to be outright false.
"Suppose we start with the assumption that rising temps cause rising CO2 levels."
Suppose so. Then where is the 800-year-old temperature rise of 1C over 50-100 years that caused this temperature rise?
Suppose that you actually LOOK at the graph. You'll see that temperatures have been lagging CO2 rises. This would indicate that, since we live in a universe where cause comes before reaction, that CO2 is causing temperature rises.