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Global Warming: Trend and Variation

Posted on 7 January 2012 by Tom Curtis

Sit on the beach and watch the tide come in.  You will see some big waves, some small.  The water's edge will advance and recede in a way that is not entirely predictable.  But there is an overall patern that emerges as the hours roll by, and the beach narrows before you.  
 
People get this.  Even the mathematically inept do not scurry to sunbathe higher on the beach if they see a larger wave in a receding tide.  They know the difference between trend and variation.
 
The difference between trend and variation can be found everywhere in our daily lives.  As this video shows, it can even be found so simple a thing as a dog being taken for a walk:
 
(Video by Teddy TV, presenter: Siffer, animator: Ole Christoffer Hager)
 
Although the distinction between trend and variation is as commonplace as an incoming tide, or a dog being taken for a walk; when it comes to climate many people seem to forget it.  They cannot find a temperature graph without seeing a trend each time the variation drifts downwards, and noise each time it goes up.   By doing so, they think they can obscure the long term trend.
 
 
Being fair, in this "dog walk" we cannot see the owner directly.  We can, however, infer his path.  It is as simple as looking for the long term trend.  So, when you try to predict likely future temperatures, are you the sort of person who looks at the dog?  Or the owner?

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Comments 51 to 87 out of 87:

  1. apiratelooksat50 wrote : "Is there definitive proof that the effect of the GHGs is enough to override the orbital factors as we should be heading into another glacial period?" As a further indication of the way things are going (not "definitive proof", of course, as anyone conversant with science knows that is rarely/ever possible), this recent article on the BBC website is worth a read : Carbon emissions 'will defer Ice Age' It's also interesting (although unsurprising) to read in that article how the GWPF (Lawson's denial group which somehow is able to function as a charity) are using such evidence (and a scientific essay from 1999) to claim that we should be adding more CO2 to the atmosphere ! Perhaps that is the next step for apiratelooksat50...?
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  2. The pirate made his case. Much of the Holocene was warmer than the present. Take a look at some hard science for a change. The ACRIM satellite shows some interesting correlations between Earth's climate and the gyrations of Saturn and Jupiter. Astrology you say? Westrology all know that correlation does not imply causation but one has to admit that Scafetta's model does a better job than any of the IPCC's models when it comes to back casting. Looking ahead, Scafetta says that temperatures are going to trend downwards while the IPCC predicts the opposite. Scafetta may be wrong but he has put forward a testable hypothesis. We won't have to wait very long to find out if his predictive skills are better than the IPCC's. One is predicting rising temperatures to 2100 while the other is predicting oscillating temperatures. What difference will it make if Scafetta is vindicated?
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    Response:

    [DB] "Much of the Holocene was warmer than the present."

    Unsubstantiated and incorrect.  Unless by present you mean about 1950 or so.  The graphic apirate uses goes through 2004 (hint:  the arrow points to it...and it is above the level of the HCO):

    Click to enlarge

    Note the temperatures in 2004 relative to 2010:

    Click to enlarge

    The present is clearly warmer than 2004 and thus the HCO.  QED.

    For greater explication of the first graphic above, please see Tom Curtis' comment at number 9 above in this thread.

  3. Pirate You might to want to read this link. Their estimate is that Milankovitch forcing at present is around 0.0 to -0.1 W/M^2. Over an entire Milankovich Cycle it is 3.4 W.M^2. In contrast a doubling of CO2 is 3.7 W/M^2. And even at the current 393 ppm that is already around 1.8 W/M^2 http://ossfoundation.us/projects/environment/global-warming/milankovitch-cycles GC "What difference will it make if Scafetta is vindicated?" Wrong question. "What difference will it make if Scafetta is NOT vindicated?" If we have the rising temps predicted, then by the time we have waited decades and decades to vindicate or not Scafetta, if he is not vindicated we are locked into a dangerous higher temperature future. So we would need profoundly strong reasons for thinking he was right, where as we have profoundly strong reasons for thing that the current understanding of Climate is right enough.
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    Response:

    [DB] Hot-linked url.

  4. (-Snip-)
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    Response:

    [DB] Off-topic links to non-science (fake-skeptic) websites snipped.

    Please constrain your comments to conform to the Comments Policy AND to the specific topic of the OP on which you are placing your comment.

    Thank you.

  5. @ DB's Moderator comment in #52: The first graphic embedded in your comment is gibberish to the average reader without a key explaining what each colored line represents and what the heavy black line represents. In addition, the dashed horizonal line is presumably the "base-line" for determing the anomoly. How was this base-line computed?
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  6. Actually, John, Tom Curtis has already ably explained that 1st graphic in his comment (#9) above.
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  7. DB - a quick aside, I agree with you on graphic #1, but I think using graphic #2 to suggest that the present is actually warmer than 2004 is a bit misleading, as the graphic is adjusted temperature. Better to use GISS or whatever to show that temperatures now are similar to those in 2004, confirming your point. What the FR figure shows is the futility of hoping it will start cooling any time soon, ie the trend underneath the variation... The overall point of your green comment is, however, absolutely right! We are now warmer than the Holocene.
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  8. ... warmer than most of the Holocene.
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  9. GC, you seem to be subscribing to "anything but CO2" (an improvement from "we are not warming") - I mean ignore good physical explanation of climate and instead looking for magical cycles. Now what would be the motivation for that? Given your comments about "billions of dollars every year", I wonder what you will think when Scafetta turns out dead wrong? Look for another magical explanation? Perhaps you might like to take the challenge here.
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  10. In that I took the simple route, you are correct sky. So let's take this a bit more step-by-step for the second part of the proof (is 2010/2011 hotter than 2004?). We know that, looking at 5 temperature records covering the past 100+ years, that the most recent decade is quite obviously the warmest in the instrumental record: And the same by looking at 10 temperature records: So, dialing it back to discerning between the years of the most recent decade we turn to Foster and Rahmstorf, who by removing the exogenous effects of various factors that add noise to the overall data, we can now see the most recent decade with increased clarity: Which was then summed up by this graphic (which I posted earlier): Lastly, we know that the 2 hottest years are: 2005 & 2010 Hindsight, being 20:20, shows the longer route does indeed provide clarity. For those preferring brevity, the route pursued in the earlier response should serve. Crumpets, anyone?
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  11. all good with me DB! The trend is, as ever, troubling.
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  12. GC - whoops missed the link. Take the challenge here
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  13. To paraphrase the Bard, "The Trend is the Thing..."
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  14. So if the observer stayed on the beach for several days, he would eventually realize that what he had mistaken for a trend was actually a natural variation, i.e. the tide.
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  15. QE: snort! If we push the analogy, we'll have to introduce something large gradually forcing a the water line to trend upward even as the tides cycle. Perhaps the underwater growth of the Kraken or a v e r y s l o w m o v i n g a s t e r o i d. Perhaps the displacement of the growing billions of boats on the water, all rising with the unlimited bounty of capitalism.
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  16. QuestionEverything, the example has nothing to do with distinguishing natural vs. man made. What it's illustrating is that you have to pay attention to timescales when claiming whether something is a long-term trend. On the scale of seconds, the waves can be considered a trend. On the scale of hours, the tide is a trend and waves are just short-term fluctuations. On the scale of days, the tide becomes short term variation. None of this tells us whether tides are natural or not. We know they are because we understand the physics behind tides, not because they happen to be periodic. There is no law that states that natural variations must be periodic or vice versa. The point is that we need to look at the appropriate timescale. When it comes to human well-being, that timescale is on the order of a human lifetime, i.e. multiple decades. On that scale, the data is clear: the earth is warming.
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  17. QE#64: Yes, the tide is a natural variation. The point here is that the trend (analogous to the rising tide) may sometimes be obscured by the noise (individual waves). If, after seeing a particularly strong wave reaching far up the beach, subsequent waves are smaller, it would be a grave mistake to say 'the tide isn't rising any more.' Another mistake is choosing to look only at the retreating waves and conclude 'its not rising.' Or look at the rising tide and say 'its cosmic rays' or some other such nonsense. End of analogy. What was your question?
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  18. QE - even natural variations must still obey the laws of physics. If you think current warming is natural, then where is the extra heat coming from? If the heat is from ocean, then why is ocean heat content increasing? If you wish to discuss further, then please go to Its a natural cycle.
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  19. Did I misread QE? I thought s/he was poking fun at the whole "it's a natural cycle" crowd.
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  20. Perhaps the displacement of the growing billions of boats on the water, all rising with the unlimited bounty of capitalism. Love it!
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  21. Sit on the beach and watch the tide come in. You will see some big waves, some small. The water's edge will advance and recede in a way that is not entirely predictable. But there is an overall patern that emerges as the hours roll by, and the beach narrows before you. This is still without doubt to me the best analogy of global warming. I use this all the time now, and kudos to whomever first came up with it!
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  22. AusssieinUSA. See my post #64. What we mistakenly think is a trend may actually be a short segment of a longer variation.
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  23. QE#72: Why do you suggest the observed trend is 'mistaken'? Please avoid vague language like 'mistakenly think' or 'may actually be.' If you are proposing 'its a natural cycle,' see the appropriate thread. If you believe in a so-called 1500 year cycle, see this thread.
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  24. And please tell us the physical basis for this proposed longer variation.
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  25. If you want an idea of the increase in sea-level over the past 170 years, Google "John Daly Sea-Level" and look at the following: The 1841 sea level benchmark (centre) on the `Isle of the Dead', Tasmania. According to Antarctic explorer, Capt. Sir James Clark Ross, it marked mean sea level in 1841. Photo taken at low tide 20 Jan 2004. Mark is 50 cm across; tidal range is less than a metre. © John L. Daly. If the benchmark is difficult to see, try these.
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  26. Fred Staples while sea level data are not my forte, I do know there are very good reasons why you can't get a good estimate of global sea levels from measurements from just one site. So perhaps you would like to explain what is so interesting about Tasmania, and why this is not just yet another example of cherry picking station data, whilst ignoring the bigger picture?
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  27. Cherry Picking? As Einstein said, “10000 observations may support a theory, it only takes one to refute it”. Science works like that. After all, the millions of stars seem set in their courses. Navigators use them every day. The earth is clearly at the centre of the universe and every thing revolves around us. Would you let a few wandering planets, and some indistinct moons, refute so well established a theory? Captain Ross marked that sea level because it was the most stable land he knew with the least tidal rise and fall. He thought future generations would be interested. Now you have a theory that human CO2 emissions will cause dangerous sea level rises. If you wish to retain that theory, you are required to explain why it has not happened in the Tasman Sea. While you are about it, you can explain the Comment from the President of the Maldives Federation on the Today programme a year or so ago. He was complaining that his entire country would be inundated if CO2 emissions continued to rise. John Humphreys asked how much the sea levels had risen so far he replied, “about a centimetre”.
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  28. Fred Staples Einstein was perfectly correct. However the the observation of sea level at one location does not refute the hypothesis that sea levels are rising or that AGW is occuring. To see why, you need to look into both the observations and the physics in more detail. Firstly not every location is a good place to cite a tide guage, because there are other factors that affect the measurements, such as glacial rebound, silting, tectonic movements etc. Also sea level does not rise uniformly around the globe (water is a viscous liquid, the distances involved are large and evaporation is not the same everywhere), so you need to take an average over multiple tide guages, preferably ones located in geologically stable locations. Which is what the scientists actually do. Was Captain Ross a geologist? Did Captain Ross have the scientific understanding of sea level that we have now? No. He was right about taking the measurements, they are indeed interesting and useful, but that doesn't mean you can ignore the wider context. If it was O.K. to pick a single data record and base your argument solely on that, why shouldn't I pick temperatures at some high Arctic station to show that global temperatures were rising very sharply? Simply because it would be a cherry pick, and would be neglecting the broader picture. What is sauce for the goose is sauce for the gander. What you are doing is equally unreasonable. The difference is that I know it is a cherry pick and wouldn't use it as the basis for a serious argument.
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  29. BTW Fred, have you performed a Google scholar search to see if you can find out whether Australia [provides] An Unstable Platform for Tide-Gauge Measurements of Changing Sea Levels or not? If it doesn't provide a stable platform, perhaps that explains why the Tasman sea tide-guages may not give a reliable indicator of global sea levels.
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  30. Fred: Sorry, that's still cherry-picking. Anecdotes from television shows, quotes from famous scientists, and measurements from a single site do not refute the aggregate of tidal gauge and satellite data showing mean global sea level rise is occuring. After all, those are all, by your own standard, observations, and each singly would be enough, by your own standard, to refute a claim that global sea level is not increasing.
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  31. Or, rather than reading the ramblings of conspiracy theorists on some random blog, we could look at what the peer reviewed scientific literature says about the Capt Ross sea marker in Tasmania; "Observations of sea level at Port Arthur, Tasmania, southeastern Australia, based on a two-year record made in 1841–1842, a three-year record made in 1999–2002, and intermediate observations made in 1875–1905, 1888 and 1972, indicate an average rate of sea level rise, relative to the land, of 0.8 ± 0.2 mm/year over the period 1841 to 2002. When combined with estimates of land uplift, this yields an estimate of average sea level rise due to an increase in the volume of the oceans of 1.0 ± 0.3 mm/year, over the same period." The amount of sea level rise varies across the globe due to effects of gravity, fluid dynamics, land uplift, and other factors. However, given that the volume of water in the oceans is increasing (due to both ice melt and thermal expansion) the long term trend is upwards... everywhere. Including this site in Tasmania.
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  32. Dikran Marsupial, Captain Ross's benchmark at Port Arthur was examined by Pugh et al, 2002. Based on that, they conclude that sea level at Port Arthur has risen 0.13 meters in the interval, or 0.8 mm per year. Fred Staples want to ignore the peer reviewed literature because some random internet guy says he should. As I understand it, here at SkS "some random internet guy" is not considered an authority. That being the case, it is up to Staples to both present the information from Pugh et al (without cherry picking), and to show why Pugh et al's conclusion is wrong. As it stands, Staples has not bothered to do that, and does not even bother reporting accurately the random internet guy who is his source. Specifically, as quoted by John Daly,
    ""My principal object in visiting Port Arthur was to afford a comparison of our standard barometer with that which had been employed for several years by Mr. Lempriere, the Deputy Assistant Commissary General, in accordance with my instructions, and also to establish a permanent mark at the zero point, or general mean level of the sea as determined by the tidal observations which Mr. Lempriere had conducted with perseverance and exactness for some time: by which means any secular variation in the relative level of the land and sea, which is known to occur on some coasts, might at any future period be detected, and its amount determined. The point chosen for this purpose was the perpendicular cliff of the small islet off Point Puer, which, being near to the tide register, rendered the operation more simple and exact; the Governor, whom I had accompanied on an official visit to the settlement, gave directions to afford Mr. Lempriere every assistance of labourers he required, to have the mark cut deeply in the rock in the exact spot which his tidal observations indicated as the mean level of the ocean."
    As can be seen, Ross had not reason to believe Port Arthur was particularly stable, and such a belief did not enter into his reasons for placing the benchmark there. As an aside, I suspect his reporting of Einstein is no more accurate than his reporting of Captain Ross. An google search of his quotation shows that Fred Staples is the only person on the internet who quotes it.
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  33. Disclaimer: Tom Curtis and I are not, in fact, sharing the same brain. Any similarities between our postings, choice of papers to cite, and/or wording (e.g. 'random conspiracy blog' / 'random internet guy') are purely coincidental.
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  34. Tom & CBDunkerson - great minds think alike! ;o) As I said, sea level observations are not my forte, but even I knew that station data are not a reliable indicator of global sea level when taken in isolation and that there were good reasons for this. I also knew that Google Scholar is a handy way of investigating whether an argument has some merit to it before I use it.
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  35. “Dikran Marsupial, Captain Ross's benchmark at Port Arthur was examined byPugh et al, 2002. Based on that, they conclude that sea level at Port Arthur has risen 0.13 meters in the interval, or 0.8 mm per year.” 0.13 meters or 5” in 172 years. We are in an inter-glacial period with a rise of 120 meters (if I remember correctly) since the last ice age. We have been climbing out of the little ice age for more than 100 years since the Ross mark was placed. Do we believe the following, unequivocally?: In 2007 the Intergovernmental Panel on Climate Change (IPCC) projected that during the 21st century, sea level will rise another 18 to 59 cm (7.1 to 23 in), but these numbers do not include "uncertainties in climate-carbon cycle feedbacks nor do they include the full effects of changes in ice sheet flow".
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  36. #85, a single site is not a good measure of global sea level rise, I'm sure you know that. Global sea level measurements are running at the top of the IPCC projections, showing they most likely underestimated sea level rise. Recent papers support this conclusion, and the IPCC SLR figure is likely to be revised upwards in the next report. So I don't believe your last para unequivocally, I think it is an underestimate! You include a couple of irrelevant points. The 120m SLR that concluded in the Early Holocene is as irrelevant to recent sea level as sea level rise in the Jurassic. Although it has some relevance for showing how much oceans can rise (and how fast - Meltwater Pulse 1A) when you melt ice sheets. The Little Ice Age is similarly irrelevant - what on earth do you suppose is the main reason temperatures have risen ~1C since the LIA, and especially since the 1960s?
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  37. Neil De Grasse-Tyson borrows an example from Teddy TV:

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