2010-08-17 04:19:08Basic rebuttal for 21: "It's just a natural cycle".
John Russell

First version to be posted shortly.
2010-08-17 20:58:05First version for comments.
John Russell


First version inviting comments...

For someone to state that the global warming we’re experiencing is actually part of a 1500-year natural cycle of global temperature variation is interesting for two reasons. First -- in contradiction to the great majority of sceptic arguments that actually deny global warming -- this argument requires that the person promoting this explanation must first agree that climate change is, indeed, happening.  Second, they must also refuse to accept the greenhouse effect, a theory first proposed more than 100 years ago and which even many sceptics of the human contribution to climate change, readily accept.

The 1500-year cycle in question has been observed mainly through ice core data as a warming in the northern hemisphere matched at precisely the same time by a cooling in the southern hemisphere. So it’s a heat distribution issue:  a global temperature ‘see-saw’ effect. The total heat in the global system remains constant.

In contrast, human-produced global warming has been caused by the rapidly increasing CO2 concentrations in the atmosphere over the last 200 years -- after remaining constant for the previous 800,000 years. And unlike natural heat variations, the current temperature increase the CO2 causes is being recorded occurring evenly all around the globe – on the ground, in the air and in the oceans.    

It appears from JC's 'medium' explanation already on the site, that there might be other cycles that need to be considered. I can't contribute to that argument as I don't have the technical background. Perhaps others can resolve the isssue and if it's decides they should be mentioned,  I'll include.

Please let me know whether the above is sufficiently correct to post in te rebuttal list.

2010-08-17 23:14:28Comment
Robert Way

There are numerous cycles and evidence for a 1050 year cycle from one of the papers he cited. (Viau et al.)

In fact Viau is someone who has taught me before and i've seen his work on this stuff and there are many cycles. I think a 300 year sun cycle a 100 year one. The evidence he used suggests that the roman warm period, medieval warm period and current warming are all part of the 1000 year cycle but that current warming is far beyond the amount of warming this cycle would cause (I think he said around 0.2 °C). Anyways, be careful in only talking about the 1500 year cycle because there are many cycles for which there is evidence. Furthermore, there is evidence that small scale cycles such as an intensification of the AMO can explain some of the warming too. I think the rebuttal is good but its a hard topic and you should perhaps bring in some more information on the subject subsequent revisions. This is a very important subject and one that is used frequently so it really has to be nailed
2010-08-18 00:00:02Cart before Horse?
John Russell


I'm happy to pull together the issues my fellow authors propose, but I need further balanced input on the facts behind this argument.

As on other topics, it seems logical to wait until the intermedate explanation has been filled out satisfactorily before trying to extract a basic explanation. To write the basic first is not sensible and I'm certainly not sufficiently qualified to tackle the intermediate.  In which case should I just wait?   


2010-08-18 01:07:34Comment
Robert Way

It is a hard question to answer. I think Johns intermediate argument came out when there was all that talk from that book about global warming every 1500 years. So in a sense its probably more aimed towards rebutting that then the question of natural cycles. The truth is natural cycles are probably contributing somewhere around 0.2 °C towards the warming of 0.8°C
2010-08-18 01:53:23


JR's remarks about mutual inconsistency between this and other skeptic arguments are useful and as well he points out w/regard to heat distribution are good.

The rebuttal will need to be backed up by a more fleshed-out intermediate treatment, though, as JR suggests.

2010-08-29 18:24:39My intermediate rebuttal
John Cook

My intermediate rebuttal sucks, basically. There needs to be a general rebuttal addressing natural cycles in general and then have a separate rebuttal specifically on 1500 year cycles. It's been on the to-do list for ages and I'm happy for anyone to throw my current rebuttal in the bin and write a new intermediate version.
2010-08-30 05:19:08Comment
Robert Way

I might take a look at it when I get a little time but this is essentially one of the hardest rebuttals to deal with because we just don't know how much of a natural cycle it is. I think that what we can say is that the early 1900s warming was likely mostly forced by natural forcings but that current warming has all the trademarks of greenhouse warming. A good example would be to point to the difference in the way that things are warming. During a natural cycle warming one would expect to see the North Atlantic warm big time if it's ocean related (through the AMO and so on) and yet we are seeing warming there of course but not completely out of whack with the rest of the world. I can't think of an eloquent way to say it but our current warming is coming from above (atmosphere) and penetrating downwards whereas early 20th century warming came from down and went up (came from the oceans with solar forcing also). Really all we can say is that we are measuring the cycles now very well and we know it can't be solar and does not seem to be coming from the oceans (are not warming enough) therefore when you eliminate all the potential contributors you are left with one major one... meh it's a hard one though
2010-08-30 05:27:24Let's start at the beginning


The basic argument that the skeptic is making is: "How do you know that the current warming is not just the normal variation of climate that has occurred over millions of years? Isn't there a natural oscillation driven by various factors that have nothing to do with human activity? In particular, what about the Dansgaard-Oeschger events that happen every 1500 years?"

I see a two-part response to this:

- Over millions of years, there are certainly climate variations; indeed over many time scales, there are temperature variations: over 100,000 years, 20,000 years, 11 years, 2 years, 1 year, 1 day. But these are not just causeless oscillations, they are driven by physical phenomena: continental drift, orbital variations, solar cycles, large-scale atmospheric modes of oscillation, seasonal variation, and daily variation (which doesn't contribute for average temperature change). Based on our understanding of these causes, we have an idea of how big a temperature change can result from any one cause, and how fast it can come on.

The problem with attributing the current warming to these non-human causes is that there is a mismatch between the rapidity of onset of change and the amount of change: It is all happening too much/too fast to meet the parameters of the natural physical causes we have identified up until now: If it were due to the same causes that drive the ice-age cycle, it should be making the current changes over periods at least 10 times longer. If it's due to continental drift, the continents have not moved appreciably in the last 150 years. If it's due to the 11-year solar cycle, how come solar luminosity has not changed as much as 1 part in 1000 in the last 20 years?

It's all very well to say "It must be due to some physical cause," but unless you have one in mind, this doesn't get us anywhere. Fortunately, there IS a physical cause that can produce this warming effect, with the right magnitude and the right timing: It's the enhanced greenhouse effect, which is caused, mostly, by additional carbon-dioxide. This has been studied for over 100 years, and if it were not happening, THAT would be a surprise.

- Concerning the Dansgaard-Oeschger events: The cause of these is still rather a mystery, but is also slightly irrelevant. According to recent evidence (http://www.realclimate.org/index.php/archives/2006/11/revealed-secrets-of-abrupt-climate-shifts/), the D-O events do not represent changes in global average temperature, but changes in transport of heat around the globe.

The discussion above is not yet intended as text for the rebuttal, but as a starting point for the ingredients of the intermediate and basic rebuttals.

- First: Does it make sense to folks?

- Second: Is anything important missing?

- Third: Need to find appropriate references and pin down the quoted numbers.







2010-08-30 06:14:25


Perhaps a generically helpful approach suitable to a basic rebuttal would be to note and acknowledge the many natural cycles steering the climate hither and thither,  tease out the top 3 of these, explore if any are so powerful they may swamp and substantially reverse what we're doing to the climate, further explore the effect of adding more impetus to a natural upswing in temperature to a weaker natural forcing.


2010-08-30 11:03:50Comment
Robert Way

Personally I agree with doug,
I think maybe you should consider talking about volcanism a bit too. It's not cyclical but it is a natural variation that affects climate and sometimes there's more activity and sometimes less. For my top 3 I would talk about Total Solar Radiation, Orbital Cycles and Ocean cycles.

Solar- Multiple cycles at 1000 year to 100 year to 11 year intervals but the 11 year and maybe 1000 year ones are strongest.

Orbital Cycles- Act slowly and our orbital configuration is now pushing towards cooling

Ocean Cycles- AMO in particular (the pacemaker of North Atlantic climate as its been called) umm AMO and NAO are linked essentially to the THC. We can use the AMO to measure the strength of the THC. We know that the AMO acts on a cycle of 40-80 years so sometimes it contributes to warming and sometimes it hides it. That means it might be hard to not implicate it. In the current warming the AMO is playing a part but is not strong enough to explain why it was this much warmer than the last peak AMO time (1940s).

Hard to really have this kind of discussion. Truthfully, I think we're talking 50% of warming since 1975 is GHG induced. That's the estimate i've seen in a paper a prof I know is submitting and I think its relatively accurate. As time has gone on, the amount of warming being human induced has increased... so say the 2000s could even be 70% GHG kinda thing...
2010-08-30 11:56:27What about reframing the question a little?
John Cook


What about if you look at it this way? Natural cycles don't happen by magic - they happen because something forces climate to change. Different solar cycles cause less or more sunlight to hit the earth. Changes in the Earth's orbit change the way sunlight hits the Earth at different times of the year. Overall, the major driver of Earth's climate is changes in the planet's energy imbalance.

We're making a major change to the planet's energy imbalance through our CO2 emissions. So it's not just a matter of eliminating the major natural cycles - we also have to stress that we are making a direct impact on climate, directly measured by satellites and surface measurements. This is the gorilla in the room for climate skeptics - all this heat being trapped by our CO2. It's gotta be doing something.

As for ocean cycles, aren't they the result of heat "sloshing around" between the various oceans and the atmosphere. Isn't that as a global warming cause eliminated by the fact that all the oceans in the world are accumulating heat? Which ties in with the fact that we're observing all this heat being trapped by CO2.

Just some thoughts, a bit disorganised, would need tying together in a more logical, coherent fashion :-)

2010-08-30 16:07:10Comment
Robert Way

Natural Cycles don't happen by magic, it is true. The problem is we don't know very well the triggers or multitude of these cycles. From what I understand there are many different solar cycles beyond the 11-year cycle we know about. There is a lot of uncertainty there but we know that there are weak solar cycles and weak orbital cycles which occur over the course of our climatic history. But yes we know these cycles all have to be forced somehow. Lets consider that evidence suggests that Solar and volcanic forcings caused a persistent La Nina like condition during the MWP which resulted in an intensification of the MOC and thus by extension a persistent positive AMO (thereby explaining North Atlantic Warmth). So yes there must be a forcing somehow. (Just a theory put forward recently mind you) The ocean cycles are not exactly sloshing around, they are more complicated. It is sometimes hard to understand their effect. If you do a simple linear regression of the AMO and CO2 forcing you can actually nearly replicate Global temperatures since 1880. It is a hard thing to understand. It is related to something called the GSA (Great Salinity Anomaly). The GSAs are actually amazing phenomena which occur in the oceans. The largest ones occurred in the 1970s in the north atlantic and in the years where they occurred temperatures were -3 °C lower than normal. That's huge really. The point of bringing it up is that there is so much uncertainty that it is hard to really make any estimates about whether we are talking redistribution of heat or not. Think of an el nino. Where does the heat come from really? That's not a redistribution...

All that being said...

We are indeed changing the energy imbalance and that should be the point of this rebuttal. We shouldn't completely dismiss the natural cycles but just show that even taking into account those cycles we can't explain the extraordinary warmth of the last 35 years.

I think a link to the empirical evidence one wouldn't hurt either.
Always been wondering why Evans (2006) is a conference proceeding and he never published his results. If they are correct they would of been the smoking gun. Might send an email sometime to find out if he did.

Another thing, A book I have that I would suggest to anyone interested in climatology

Earth's Climate: Past and Present by William F. Ruddiman

It is actually quite good and very readable. Definitely worth it.

2010-08-31 02:57:25Move this one forward.
Jim Meador


As I see it, there is a bit of housekeeping to do and then this is quite worthy of publication.

 1) Rename the skeptic argument as "It's just a 1500 year cycle" to clear up the ambiguity about which skeptic argument we are talking about. Since a book has been published on the subject, it seems to be a skeptic argument worthy of addressing.

2) Publish this as a rebuttal to the claim. 




2010-09-04 01:22:02


Looking at this again I agree w/Jim, this is quite sufficient for helping somebody who has an open mind.  

"...variation is interesting for two reasons..."

I frequently catch myself using the term "interesting" when I don't really mean it. In this case I'd try "myopic" or just plain "wrong."

2010-09-04 02:51:54if 1500 year cycle
Dana Nuccitelli

If this were used to rebut the 1,500 year cycle only, as suggested by Jim, it would be a good idea to point out that the two previous 'warm periods' (MWP and Roman) were about 1,000 and 2,000 years ago, not 1,500 and 3,000.  So the math simply doesn't add up.  It's a very simple rebuttal of the 1,500 year cycle argument.

I agree, rebutting 'natural cycles' in general will require a lot of research.

2010-09-04 03:11:12Comment
Robert Way

I really think this argument should be changed to there is a 1500 year cycle or something of the sort because omitted other cycles is not a good way of addressing this issue. There is in fact a 1000 year cycle roughly which has played a part in MWP ,RWP and modern warming. We should just look at changing it to the one cycle and addressing the natural cycle argument in an appropriate intermediate response and bring it down to basic after.
2010-09-04 18:08:49Agreed
Graham Wayne
Yep - I'm with Jim and Doug...neither of which have bought a round yet, you cheapskates :)
2010-09-10 06:15:14Rebut 21, Natural Cycle

I think this is OK as basic. Now I am eager to see an Intermediate and advanced!
2010-09-10 12:20:11Thumbs up for 1500-year cycle
James Wight

Works okay as a rebuttal to “It’s a 1500-year cycle”, though not comprehensive enough for “It’s just a natural cycle”.
2010-09-10 19:53:00
Rob Painting
Another vote for 1500 year cycle rebuttal.
2010-09-19 17:41:23Published
John Cook

Changed the argument to "1500 year cycles", added some hyperlinks, tweaked some of the text in the final paragraph because I could see some sharp eyed skeptics jumping down the throat of some of the wording.
2010-09-19 17:49:22Oh and I removed the intermediate rebuttal
John Cook

No point keeping it as it was just the green box summary, no actual content there. So I've unclaimed the intermediate version, open to whoever wants it :-)