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What has global warming done since 1998?

What the science says...

Select a level... Basic Intermediate

For global records, 2010 is the hottest year on record, tied with 2005.

Climate Myth...

It hasn't warmed since 1998
For the years 1998-2005, temperature did not increase. This period coincides with society's continued pumping of more CO2 into the atmosphere. (Bob Carter)

No, it hasn't been cooling since 1998. Even if we ignore long term trends and just look at the record-breakers, that wasn't the hottest year ever. Different reports show that, overall, 2005 was hotter than 1998. What's more, globally, the hottest 12-month period ever recorded was from June 2009 to May 2010.

Though humans love record-breakers, they don't, on their own, tell us a much about trends -- and it's trends that matter when monitoring Climate Change. Trends only appear by looking at all the data, globally, and taking into account other variables -- like the effects of the El Nino ocean current or sunspot activity -- not by cherry-picking single points.

There's also a tendency for some people just to concentrate on surface air temperatures when there are other, more useful, indicators that can give us a better idea how rapidly the world is warming. Oceans for instance -- due to their immense size and heat storing capability (called 'thermal mass') -- tend to give a much more 'steady' indication of the warming that is happening.  Records show that the Earth has been warming at a steady rate before and since 1998 and there is no sign of it slowing any time soon (Figure 1).  More than 90% of global warming heat goes into warming the oceans, while less than 3% goes into increasing the surface air temperature.

Fig 1

Figure 1:  Land, atmosphere, and ice heating (red), 0-700 meter ocean heat content (OHC) increase (light blue), 700-2,000 meter OHC increase (dark blue).  From Nuccitelli et al. (2012).

Even if we focus exclusively on global surface temperatures, Cowtan & Way (2013) shows that when we account for temperatures across the entire globe (including the Arctic, which is the part of the planet warming fastest), the global surface warming trend for 1997–2012 is approximatley 0.11 to 0.12°C per decade.

Last updated on 4 March 2014 by LarryM. View Archives

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Further reading

Tamino further explores the warming trend since 1998 in Garbage is Forever and Wiggles.

I've kept my original treatment of the subject as other websites hotlink to the images. My original treatment uses similar arguments to Fawcett and Jones 2008 although their analysis is much more rigorous (as you'd expect in a peer-reviewed paper).

Further viewing

Comments

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Comments 201 to 215 out of 215:

  1. Peter42, if your basic question is "what would convince me that non-significant or no warming is taking place," then the answer is "non-significant or no warming taking place." If, instead, you're asking about AGW fundamentals, then I'd have to be provided with a comprehensive physical model that did not allow CO2/H20/et al. to absorb and emit within the range at which the sun-warmed surface of the Earth emits, and one which did not allow cooler "objects" to radiate toward warmer "objects."

    Absent that alternative model, anthropogenic global warming must be taking place. Is some cooling factor countering the warming? Perhaps, but that doesn't mean the GHG factor has stopped doing its thing. If insolation drops and aerosols increase, both providing overwhelming cooling effects, does that mean that AGW is not occurring? No. The warming--or, as some semantic trolls like to have it, "the slowing of cooling"--is still occurring, even when the temperature is trending down. That's what Foster & Rahmstorf (2011) partially addresses. Strip away the major cooling/warming factors (solar, ENSO, volcanic) other than GHG, and what do you have left?
  2. Also missing is the other important question. Given the strong internal variation, what is the shortest time period over which the predicted warming trend could be detected? Estimates are somewhere around 17-20 years unless you strip out some of the known natural variability like Foster and Rahmstorf did. So your statement "According to the latest HadCRUT4 data, there is no statistically significant increase in temperature (0.083C/dec +/-0.172C/dec)" applies to which period exactly?
  3. How does the current "man is causing global warming" theory jive with the facts that the earth has normal cooling (glacial) and warming (interglacial) cycles? According to my research, it is a fact that we went into a interglacial period (global warming) over 11,000 years ago. So, yes we are in global warming and its cause had nothing to do with man's activities because there weren't many humans 11,000 years ago and the humans that were around didn't drive vehicle or have power plants. Interglacial periods, from my research, can last 40,000 years. My take, considering the above facts, is that man's involvement with global warming is insignificant, it's going to happen with or without man, just like the next glacial period will.
  4. michaelcomaha:

    Your inquiry is off-topic on this post.

    To point you in the correct direction (both in terms of re-posting your inquiry should you desire and as an answer) please click on the #1 most used climate myth.
  5. michaelcomaha @203, as Composer @204 notes, your inquiry would be more appropriate in the 'climate's changed before' discussion. However, it's worth briefly noting that the planet had been cooling since about 8,000 years ago until about 150 years ago. While there is warming leading into an interglacial, the interglacial periods themselves are relatively stable and generally slightly cooling.
  6. michaelcomaha, I have responded in a more appropriate place.
  7. According to my research...


    Although it's a response to an off-topic comment, it has general applicability so I will note that it seems to be a characteristic of many non-scientists that they think that reading a few unreferenced, out-of-context sources constitutes "research".

    It doesn't.

    'Real' research is a systematic and thorough process that involves assessing both a broad and a representative section of the area being studied, and doing so in a manner that minimises any personal bias input. Research also requires some understanding of the basics underpinning the field being investigated,in order that the data acquired is properly analysed.

    What michaelcomaha did, as so many other non-scientists do who want to pretend at making a scientific point, was to simply cherry-pick one or two factoids with which to construct the illusion of having a clue, and a point.

    He has neither, because he did no actual, real research. He simply read some stuff.
  8. 203, michaelcomaha,

    As others have pointed out, this needs to be discussed elsewhere, but before you go there to pursue the topic further (as I hope you will), one key point...

    Interglacials can last a long time, but their duration is not random. We well today understand the orbital forcings behind the glacial transitions (not completely, no, there are lots of gaps, but well enough).

    The fact is that temperatures for the current interglacial peaked about 8,000 years ago, then started to decline, and should still be declining on the way into the next glacial period.

    So while a cursory glance at glacial periods suggests that you can ignore current warming, a closer and more educated view of the subject suggests that your own argument shows that you should be even more alarmed than you might have been before.

    Beyond this, it is also virtually certain that we have guaranteed that the Earth will skip the next glacial period, in spite of the orbital forcings. CO2 levels will not fall enough to permit another glacial period to completely occur (I'm not saying that's a bad thing, just that it's true).
  9. Hi, I know that there have been ice ages in the past, and even during the middle ages (mini ice age). I would like to see how the temperature of the earth has increased since the last ice age and whether we are seeing an increase that has been happening for a long time rather than just during the industrial era. I haven't heard anyone explain the global warming that began at the end of the mini ice age in the middle ages. Just to put this in perspective, the sea levels during the last ice age were hundreds of meters below the current level and I see nothing that links those levels with the current levels and the changes is sea levels and temperatures over the long term.
  10. Steve, this post Is sea level rise accelerating? shows an acceleration in sea level rise corresponding to recent CO2-induced warming on top of the ongoing rise since the end of the LIA in the 1800's or so. The explanation of the global warming that ended the LIA is here
  11. Steve at #209:

    I would like to see how the temperature of the earth has increased since the last ice age and whether we are seeing an increase that has been happening for a long time rather than just during the industrial era. I haven't heard anyone explain the global warming that began at the end of the mini ice age in the middle ages.


    If you haven't "seen" anything or "heard" any explanation, then you are simply demonstrating that you are ignorant of the science.

    There's a whole Interweb out there with which you can UTSE, or you could go through Skeptical Science's own archives to find the relevant commentary.
  12. Steve, I have responded on a more appropriate thread.
  13. Britain's Met Office’s Hadley Centre is said to be reporting that there has been no warming for the past 15 years. What do you make of this?
    Response: That "saying" is incorrect. See the Skeptical Science rebuttal.
  14. Rosco, that is news to me. Can you provide a link to their research that says "that there has been no warming for the past 15 years"? It must be powerful stuff, to overturn the laws of physics and the metrics of ocean heat content.
  15. In section:

    Is 1998 actually the hottest year on record?

    you have a link for:

    A new independent analysis of the HadCRUT record sheds
    light on this discrepancy ...

    with the URL of:

    http://www.metoffice.gov.uk/corporate/pressoffice/2009/pr20091218b.html

    This URL no longer exists; the new URL is:

    http://www.metoffice.gov.uk/news/releases/archive/2009/land-warming-record

    -scott
  16. "Is 1998 actually the hottest year on record?" In the contiguous US 1998 is the warmest year on record. The trend since then, however, has been down. 2012 is almost certainly to be the "new" warmest year on record in the US. Nevertheless, the 1998 record high annual temperature will have to be broken by almost two full °F for the downward trend to be broken. This seems unlikely. But, who knows, 1917 is the coldest year on record and it was replaced by the warmest in just four years. The average annual temperature went up 3.7°F from 1917 through 1921.
  17. plfreeman?

    So... what ever happened to plfreeman, who was going to re-analyze your data and come up with better curves?
    Response: [DB] That was the only comment ever placed at SkS by that person.
  18. I just looked at the datafiles from GISS, HadCru 3, RSS, & UAH (yes, you can download them yourself and plug them into a spreadsheet and see for yourself). Since everywhere I turn there is a different version, I needed to check for myself.
    For the last 15 years (December 1997-November 2012), here are the trends:
    GISS: +0.1 C/decade
    HadCru 3: -0.008 C/decade
    RSS: -0.01 C/decade
    UAH: +0.05 C/decade

    So, according to the climate records as of December 2012, warming has stopped for all practical purposes since 1998 (a mean warming trend of 0.02 C/Decade is close enough to 0 that only a zealot would argue the point).

    I also noticed there is a considerable gap forming between the records, if normalized to January 1980. (-intimations of dishonesty snipped-).
    (In all fairness, RSS and UAH are very close, HadCru 3 is in between those 2 and GISS, which shows the most warming)
    Response:

    [DB] You knowingly or unknowingly prosecute a meme. A meme based on a lack of understanding of statistical significance. One detailed in this recent blog post here.

    Furthermore, when applying the Foster and Rahmstorf methodology, the global warming trend in each of the major data sets IS statistically significant since 2000.

    http://www.skepticalscience.com/foster-and-rahmstorf-measure-global-warming-signal.html

    http://www.skepticalscience.com/still-going-down-the-up-escalator.html

    Please read them for enlightenment.

  19. Just read them, thank you.
    I fear those sorts of articles give the public serious doubts about the science of AGW.
    (-intimations of impropriety snipped-)
    Response:

    [DB] Arguing from ignorance and an incomplete understanding of the science, compounded by accusations of impropriety and academic fraud detract from your credibility. If you dispute the content of the linked posts, discuss your concerns there, not here.

    For posts discussing why the PDO is not responsible for the observed warming trend, use the Search function in the upper left portion of any page here for an appropriate place to learn...and then discuss, if need be.

    Again, read the Comments Policy (link adjacent to every Comments Box)...thoroughly. Future comments constructed such as this one will be summarily deleted in their entirety.

  20. Question : I have found on another web site a neat looking plot of temperature versus year going well back in time. It states that this graph is from SKS and consists of 11 different temperature records averaged. If indeed this graph comes from SKS can anyone tell me where to find it here? It would seem that this graph would be on topic for this thread, if indeed that web site was correct. Sorry I cannot be more specific about where I found the graph, I lost those notes. I would keep digging further until I found it again if there is an interest.
  21. The simple fact is there has been a 16-year halt in warming, in stark contrast the the 30 years before that.

    This though is still short in climate time-scales, and other indicators have *not* stopped moving, eg ocean temperatures, arctic melt, CO2 rising faster than ever.

    But since the basic mechanism of greenhouse warming is that the atmosphere warms due to CO2 trapping longwave radiation (leading to overall warming), this suggests the warming of the oceans *cannot* be a consequence of greenhouse warming (since the atmosphere is not warming).

    It must be something else - but what ?
  22. Yawn. Punksta spreads FUD ("halt in warming"? Really???) by ignoring the 97.7% of the land surface/oceans/cryosphere (the oceans and the cryosphere) which, inconvenient to his messaging, indelibly show warming, by drilling down to that which shows the least warming over that period, the land surface.

    In fact, when applying the Foster and Rahmstorf methodology, the global warming trend in each of the major data sets IS statistically significant since _2000_ (yes, even less than 16 years)
    • http://www.skepticalscience.com/foster-and-rahmstorf-measure-global-warming-signal.html
    • http://www.skepticalscience.com/still-going-down-the-up-escalator.html

    And even further evidence that the warming continues (topical data: whodathunkit?):
    • http://www.skepticalscience.com/global-warming-lesson-for-monckton-and-co.html

    Fun fact skeptics like Punksta hate #1: The oceans have been gaining 2 Hiroshima bombs worth of incremental energy PER SECOND since 1961. Unabated.

    Specifically, the total heat content change from 1961 to 2011 (50 years) is approximately 21 x 1022 joules. That's about 210000000000000000000000 joules (a joule is 1 watt for 1 second; so a 100 watt light bulb will use 100 joules in 1 second).

    That's a BIG number but somewhat unreal. So how much energy is this? What could it do? What is it in the real world, where we don't routinely look at numbers that big. That is HOW Big...?

    This is a rate of heating of 133 Terawatts (or 0.261 Watts/m2). 133 Terrawatts is 2 Hiroshima bombs a second. Continually since 1961.
    Every. Second. Of. Every. Day. For. 50. Years.

    The reality is, due to the radiative physics of CO2, there is an energy imbalance in the Earth's energy budget. As a result, the Earth system (land surface, oceans and its cryosphere) is still accumulating energy, unabated.

    "Skeptics" like to focus on the tiny 2.3% of the system, the surface temperature record, and then further focus on just 2% of that (the United States) in an effort to distract. Essentially, it's a game of "LOOK!!! Something shiny!!!"
    • http://www.agu.org/pubs/crossref/2012/2012GL051106.shtml
    • http://www.skepticalscience.com/Breaking_News_The_Earth_is_Warming_Still_A_LOT.html

    Fun fact skeptics like Punksta hate #2: That El Nino years, La Nina years and even ENSO-neutral years are all rising in temperature over time (warming).
    • http://www.skepticalscience.com/john-nielsen-gammon-commentson-on-continued-global-warming.html

    Basically, Punksta is still playing on the Escalator...except he's trying to go Down the Up Escalator.
    • http://skepticalscience.com/still-going-down-the-up-escalator.html

    The world warms; humans are the cause of it. Life sucks for fake-skeptics, as the incontrovertibly inconvenient data and physics are against them. Facts, like tiggers, are wonderful things, for those who have them.
    "I have never made but one prayer to God, a very short one: "O Lord make my enemies ridiculous." And God granted it. ~ Voltaire"
  23. Daniel,
    You have completely misread my post - I explicitly note that the oceans (a far larger heat-sink) are warming.

    My point is merely that
    * greenhouse warming works by warming CO2 in the atmosphere
    * the atmosphere has stopped warming
    Therefore, warming of the ocean cannot be due to CO2/atmospheric warming.
  24. Punksta - The oceans absorb shortwave radiation from the sun, and release it out to space at a rate that is to some extent dependent on overturn rates. Over the last 16 years or so we've seen a rather huge El Nino (pushing heat out to the atmosphere, ~0.2°C or so above the general trend) followed by several La Nina's (absorbing energy from the sun more efficiently, cooling the atmosphere ~0.2°C below the general trend).

    Really - there are no surprises here. The 2-3% of the thermal mass of the climate represented by the atmosphere is showing some noise due to (primarily) variations in ocean overturning, but the 95% or so that are the oceans are still showing warming.
  25. KR,
    You don't mention rising CO2 - which means you agree it is not implicated in ocean warming ?
  26. Punksta @221:

    1) NASA's Gistemp shows a warming trend of 0.087 C per decade over the last sixteen years; or 0.139 C per sixteen years. Deniers may want to call that "no warming" or a "halt in warming"; but that tells us only about their honesty. "The warming is not statistically significant" does not mean "there is no warming", anymore than "the pregnancy test was inconclusive" means "you are certainly not pregnant".

    2) Contrary to your claim, the physics of the greenhouse effect do not predict that the atmosphere will be warmed first. Rather, they predict that the accumulation of energy at the Earth's surface (warming) will not stop until surface temperatures have risen sufficiently to restore radiative balance at the top of the atmosphere. Your silly claim that:

    "But since the basic mechanism of greenhouse warming is that the atmosphere warms due to CO2 trapping longwave radiation (leading to overall warming), this suggests the warming of the oceans *cannot* be a consequence of greenhouse warming (since the atmosphere is not warming)."


    only shows that you, like most so-called "skeptics", have not bothered to learn the theory before you declare it refuted.

    This urgency to declare a theory refuted despite not even understanding it shows that it is not scientific understanding that motivates the rejection of climate science.
  27. Tom,
    1) Warming is not at all like pregnancy - statistical significance matters. At least to those whose agenda is true science.

    2) The physics of greenhouse warming says that the CO2 traps heat. This necessarily means that the without heating of CO2, and hence of the atmosphere, there can be no knock-on warming elsewhere. Nothing you have said gainsays this. Indeed you yourself speak of a continuing warming of the surface.
  28. Punksta @ 227, you say "The physics of greenhouse warming says that the CO2 traps heat". Does it? I thought the theory said a molecule of CO2 captures an IR photon and either re-radiates the IR in a random direction, or excites an air molecule by collision. Nothing about 'trapping heat', per se, in that, is there?

    Of course, I don't have the advantage of your grasp of physics. I would be truly grateful if you could prove AGW theory wrong, as I am currently mildly alarmed by the evidence.
  29. Punksta @227:

    1) Prattling on about your "agenda is true science" does not turn an indeterminate test ("the warming is not statistically significant") into a determinate falsification ("there has been a 16 year halt in warming"). Misinterpreting tests of statistical significance is not a mark of true science, but of propaganda, pure and simple. If you wanted to interpret the test accurately you would note that, not only does the test over 16 years of data not exclude zero warming; but it also does not exclude warming at greater than the IPCC predicted rate.

    The key question then is, if you expand the period under consideration until the trend is statistically significant, does it show warming or not. Want to take a bet on what it shows? Or will you chicken out and show that propaganda is your aim with your misrepresentations of science and scientific method?

    2) I have written an introduction to the physics of greenhouse here. In a nutshell, the greenhouse effect works because atmospheric CO2 is cooler than the surface. As a result, when it absorbs surface radiation it is more likely to loose the energy gained through collision than remision, resulting in less power being emitted. This reduction in emitted radiation requires compensating increases elsewhere, which can only be achieved by the surface warming.

    So, contrary to your understanding, increased air temperature reduces the outgoing radiation at the Top of Atmosphere, thereby resulting in an imbalance. If an imbalance already exists, and the atmosphere does not warm, then the imbalance will not be reduced, with the consequence that more energy will be absorbed at the surface than if the atmosphere had warmed.

    Bizarrely, with your clear misunderstanding of the physics, you have got it exactly backwards.
  30. Doug H @ 228
    ...Nothing about 'trapping heat', per se, in that, is there?
    Well, it is implied, and quite in agreement with what you said. The randomly directed re-radiated IR will only reach earth or space if there is a free path for it. Otherwise it will be absorbed by another CO2 molecule. And so on ... It's all about the 'mean free path' as I understand it.
  31. General comment

    It’s quite obvious that Punksta is talking in circular riddles, an art perfected by climate denier bloggers. He/she is jumping from one thread to another using the same silly red herrings.

    We can only hope this denier tires and goes away or the moderator enforces SkS’s site policy on this well recognised technique.

    I would like some questions answered properly though.
  32. Tom Curtis @ 229

    1) Denying the 16-year warming hiatus is pure propaganda.

    the greenhouse effect works because atmospheric CO2 is cooler than the surface ...

    No, it works because of the absorption spectra of GHGs.
    However, you do correctly conclude (albeit for the wrong reasons), that the surface warms as a result. Which means that if the surface is *not* warming, then the greenhouse effect is *not* in evidence.

    increased air temperature reduces the outgoing radiation at the Top of Atmosphere

    Yes, a warmer atmosphere slows the cooling of the oceans into the atmosphere. But, again, if the atmosphere is not warming, it cannot be slowing the cooling of the oceans into itself.

    So if the oceans are indeed cooling, it must be something other than increased GHGs at work.
  33. Punksta wrote:

    "1) Warming is not at all like pregnancy - statistical significance matters."

    In that case, can you tell me exactly what it means for the observed trend to be not statistically significant?

    For example, does that mean that there has been a pause in global warming?
  34. In a rational conversation, the conversation progresses by people responding to the points that others have made. They do not simply yell more and more loudly the same slogan again and again. Punksta clearly is incapable of the former, and relies slowly on the frantic repetition of his slogan.

    Nothing is gained by conversation with a person that committed to irrationality. Consequently, I will simply note that:

    1) Puncksta continues to insist that 0.14 C of trend warming over the last 16 years (gistemp) is no warming at all because it fails a test for statistical significance. He also no insists that noting that there has in fact been a warming trend over the last 16 years (even though all five major temperature indices show warming over the last 16 years) is propaganda. his world is so inverted that simply describing the situation accurately becomes, to his mind, propaganda.

    2) He has clearly not bothered to read the introduction to the greenhouse effect that I linked to. Had he done so he would have seen that his objection to my description was in fact part of my description. Anybody confused by Punksta's bluster about absorption should think about what the effect of CO2 would be if the atmosphere was the same temperature as the surface, or warmer than it. In the later case, for example, adding greenhouse gases will cool the surface . I discuss this situation in a comment here (as does Chris Colose in the following comment).
  35. Punksta @232:

    (1) Trends 1996.92 to 2012.83 (ie, the most recent 16 years of data):

    Gistemp: 0.087 C per decade (0.139 trend increase in temperature over the 16 years).

    NCDC (NOAA): 0.047 C per decade (0.075 trend increase over the 16 years)

    HadCRUT4: 0.053 C per decade (0.085 trend increase over 16 years)

    UAH: 0.093 C per decade (0.149 C trend increase over 16 years)

    RSS: 0.003 C per decade (0.005 C trend increase over the 16 years).

    Of these, Gistemp is the most accurate in that it:
    a) Alone of the three surface temperature indices, has global coverage;

    b) Has more stations than NCDC, and significantly more stations than HadCRUT4; and

    c) It is a surface record, and is not contaminated by data from the stratosphere (which is cooling) as is the case with RSS and UAH.

    I note that a 0.03 C decadal trend taken over 16 years is a trend increase of 0.048 C, so even Punksta's cherry picked data set with its cherry picked period does not give a result of no warming, contrary to Puncksta's claims. It also leave grave doubts as to his maths, as he apparently thinks 16 years equals 10 years (to expect only a decades warming over the full 16 years); and that 0.048 = 0.

    Once again, there has been a warming trend on all data sets over the last 16 years. That trend has not been statistically significant on any data set. That just means that on all data sets, the error bars are wide enough so that they do not exclude underlying trends equal to zero, or indeed, equal to or greater than the IPCC predicted warming.

    Dressed up in its best form, Punksta's argument comes down to the inference:

    If we restrict our data to just the last 16 years, there is insufficient data to conclusively determine that the trend is not zero, or to determine that the trend does not equal the IPCC predicted trend. Therefore, the IPCC predicted trend has been falsified.
  36. (-sloganeering snipped-).
    Response: [DB] Please respond to Dikran's question above:
    "In that case, can you tell me exactly what it means for the observed trend to be not statistically significant?"
  37. Punksta, suppose that air temperatures went up for 30 days in the Spring, but then for the next 16 days there was no statistically significant warming. Meanwhile the oceans continued to warm slightly.

    Would you argue that this was conclusive proof that the cycle of the seasons was not causing the warming of the oceans or the previous warming air temperatures?

    This is a direct parallel to your argument 'against' global warming and ought to make clear why it is wrong.

    There was a study about a year ago that found the minimum period needed to establish a statistically significant trend in global temperatures was about 17 years. They could have saved the effort and noted that 'skeptics' so frequently use 'no warming for 15 / 16 years' to surmise that the boundary must be a year higher.

    Put another way... there hasn't been a statistically significant 'cooling' or 'flat' global temp anomaly trend since the 70s.
  38. Punksta seems to come from a long, long, long line of denialists who are ignorant (often deliberately so...) of the fact that a minimum amount of time is always required to be able to identify a signal emerging from inherently noisy data.

    I have two points, in addition to the many others made above, to put to this person. The first is an exercise in thinking (yes, I am being optimistic...):

    1) If there had been no "statistically significant" warming for twelve years, does this disprove a relationship between CO2 and warming? If there had been no "statistically significant" warming for ten years, would this disprove a relationship between CO2 and warming? Five years? Two?

    What is the basis for claiming that there is no relationship between CO2 and planetary warming?

    2) using the trend calculator to which many people have directed Punksta, I constructed a graph showing how many years prior to a particular year are required to identify a statistically significant warming trend at the 2 %sigma; (~95%) level. It's quick and dirty - I didn't muck around with the autocorrelation period and I only used GISTemp - but it's enough to demonstrate for any year in the last three decades how many years of prior data was required to observe a "statistically significant" warming trend.



    The graph itself shows two further things:

    1) there is nothing unusual about the current period required to identify statistically significant warming - indeed, over all there is a trend to the period becomng shorter.

    2) prior to 1981, the post-World War II hiatus (significantly attributable to aerosols) triples the period required to identify warming. However, there was warming occurring then too, but it was being compensated for by other factors. This did not alter the physics of greenhouse gases though, and the same is the case today - CO2 is still warming the planet.


    [I apologise for thumb-nailing the image. Try as I might, my efforts to use the width tag would not produce a visible graph.]
    Response: [DB] Improved image width. Bernard, I tried to email you the proper image width code but the message proved undeliverable.
  39. I should probably explain the approach that I used to determine the intervals I derived for the post above.

    All I did was enter various start years until I obtained for each of the end years a minimum-sized interval where there was no way to describe a negatively-sloped line through the whole range. It's not the best way to derive the info, but it was quick and it's a good approximation and I didn't want to waste time with something that has been debunked countless times in the past.
  40. Neat image Bernard!
  41. Punksta, even based purely (and therefore inappropriately) on statistics, the +0.14 C trend of the last 16 years is the most likely "true" value--the expected value. 0 is not the most likely value. Nor is +0.13, nor is +0.15. But trend values close to +0.14 are more likely to be the "true" value than trends far from it are. Statistical significance merely provides one estimate of the probabilities of those different trend values.

    Nor is there anything magical about the 95% confidence level; it is merely a traditional value. The 94% confidence level encompasses only values closer to the 0.14 most likely value. Statistics does not dictate what the confidence level should be. The situation outside of statistics dictates that. If you must make a decision based on your best estimate of the true value, you must weigh the costs and benefits of acting based on the several incorrect and correct decisions you might make based on that best estimate. You leaven those costs and benefits with the probabilities of the various errors and correct decisions. But even if you do make such a sophisticatedly thorough judgment, you are a fool if the statistics are the only knowledge you use to make your decision. Knowledge of physical processes such as causality, and a plethora of other factors, should be even more important in your decision. Statistics is merely one tool in a very large scientific toolbox.

    This failure of pure statistics to provide clear answers is not at all unique to climatology. I used to do massively complex ANOVAs in a completely different field, and usually had difficulty dissecting the complex relationships because the component, less complex statistical tests rarely were significant at the same probability level for them to logically support the overall, complex test. In other words, a naive perspective on the entire set of tests would be that they were internally inconsistent and therefore nonsensical and impossible. That's a similar phenomenon to what folks here have pointed out to you: Often all the short time intervals fail to reach significance at the same probability level as the longer time interval. That's why real scientists do not base their judgments solely on statistics, and even to the extent that they do rely on statistics, they do not rely on a naive, high school level of statistics.
  42. DB at #238.

    Thanks for the tweak. I'm not sure what the issue is with my addie - I tried mailing it from my institutional address, and there was no problem.

    I shall have to remain intrigued, and wondering... ;-)
  43. The link to Bob Carter's Telegraph article no longer works. It has moved to: There IS a problem with global warming... it stopped in 1998
  44. Simon @ 243, Bob Carter's Gish Gallop is still worth reading, as an example of faulty reasoning by someone who should know better. His opposition to AGW seems rooted in his politics, rather than in his superior understanding of the evidence. No doubt, this polarised view is being passed on to his students. Sad to see.
  45. Hi dikran

    where is  the global warming :)

  46. what is wrong with this graph

  47. Warren Hindmarsh, two questions:

    Did temperature rise or stand still over the course of the twentieth century?

    If the warming rate over a given period is greater than in a period over which temperatures are known to rise, is it correct to say that temperatures are not rising?

  48. sorry Dipal have to go right now

    The graph is from

    The Hadley Centre/CRU records show no warming for 18 years (v.3) or 19 years (v.4), and the RSS satellite dataset shows no warming for 23 years (h/t to Werner Brozek for determining these values). 

  49. A third question:

    Isn't it misleading to say that a period with a positive tempertature trend (ie, temperatures are rising) shows no warming?

     

    Please note that "no warming"  does not mean the same thing as "the warming is not statistically significant".

  50. Warren Hindmarsh wrote: "what is wrong with this graph"

    Read up on 'cherry picking'... that is, deliberately choosing a time period which shows the result you want despite the fact that longer and/or shorter time periods show results contradicting your claim.

    Also: "temps have been rising slowly since the middle ages"

    Not according to any historical temperature study I am aware of. Indeed, temperatures were slowly falling for thousands of years, including both before and after the 'middle ages', until the modern greenhouse warming surge.

    Finally: "but for the last 17yrs or so [temps] have stablized"

    Again, 'cherry picking'... not only of the time period, but also which temps. Ocean temps have certainly not 'stabilized' over the past 17 years.

    You obviously didn't even bother to read the post above. Maybe try that before making arguments which it has already disproved.

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