RealClimate logo

Mind the Gap!

Filed under: — rasmus @ 18 November 2008 - (Italian)

Mean temperature difference between the periods  2004-2008 and 1999-2003
Confusion has continued regarding trends in global temperatures. The misconception ‘the global warming has stopped’ still lives on in some minds. We have already discussed why this argument is flawed. So why have we failed to convince ;-) ?

The confused argument hinges on one data set – the HadCRUT 3V – which is only one of several estimates, and it is the global temperature record that exhibits the least change over the last decade. Other temperature analyses suggest greater change (warming). Thus, one could argue that the HadCRUT 3V represents the lower estimate, if a warming could be defined for such a short interval.

Global mean temperature estimates: CRU, NASA-GISS data and the NCEP and ERA40 re-analyses
A comparison with other temperature analyses, such as the NASA/GISS (pink in the figure on the left), reveals differences. We can also compare with model-generated data (re-analyses), keeping in mind that one must be very careful with these data since they are not appropriate for studying long-term climate change (they give a misrepresentation of trends – at least on a local scale). Nevertheless, information from independent data suggest an increase in global mean temperatures even over the last decade.

All scientific questions involve some degree of uncertainties (error bars), and these can only be reduced if one can prove that they are influenced by an external factor (‘contamination’) or if some of the data are not representative for the study. Hence, if some of the data are incorrect, then it’s fair to exclude these to reduce the error bars. But this requires solid and convincing evidence of misrepresentation, and one cannot just pick the low values and claim that these describe the upper limit without proving that all the data with higher values are wrong. In other words, arguing that a lower limit is the upper bound is utter nonsense (even some who claim they are ‘statisticians’ have made this mistake!).

Another issue is that some of the data – i.e. the data from the Climate Research Unit (CRU) – have incomplete coverage, with large gaps in the Arctic where other data suggest the greatest increases in temperature. The figure below reveals the holes in the data knowledge. The figure compares the HadCRUT 3V data with the NCEP re-analysis.

Temperature measurements over the Arctic: CRU data and the NCEP re-analysis
Figure caption: The difference between Oct. 2007 – Sep. 2008 temperature average and the 1961-1990 mean temperature for HadCRUT 3V (upper left) and NCEP re-analysis (upper right). Below is a comparison between the 12-month 60N-90N mean temperature evolution (red=NCEP, black = HadCRUT 3v)). (click on figures for PDF-version)

Re-analysis data are results from atmospheric models where observed data have been fed into the models and used to correct the simulation in order to try to get a best possible description of the real atmosphere. But it’s important to note that the NCEP re-analysis and other re-analyses (e.g. ERA40) are not regarded as being appropriate for trend studies due to changes in observational systems (new satellites coming in etc). Nevertheless, a comparison between the re-analyses and observations can highlight differences, which may suggest where to look for problems.

Mean temperature difference between the periods  2004-2008 and 1999-2003
The animated figure shows the temperature difference between the two 5-year periods 1999-2003 and 2004-2008. Such results do not show the long-term trends, but it’s a fact that there have been high temperatures in the Arctic during the recent years.

The recent Arctic warming is visible in the animated plot on the right showing the NCEP re-analysis mean temperature difference between the periods 2004-2008 and 1999-2003.

The NOAA report card on the Arctic was based on the CRUTEM 3v data set (see figure below) which excludes temperatures over the ocean – thus showing an even less complete picture of the Arctic temperatures. The numbers I get suggest that more than 80% of the grid-boxes north of 60N contain missing values over the most recent decade.

Temperature measurements over the Arctic: CRU data and the NCEP re-analysis
Figure caption: The difference between Nov. 2007 – Oct. 2008 temperature average and the 1961-1990 mean temperature for CRUTEM 3v (upper left) and NCEP re-analysis (upper right). Below is a comparison between the 12-month 60N-90N mean temperature evolution. (click on figures for PDF-version)

The funny thing, however, is that the last decade of the Arctic CRUTEM 3v temperatures are closer to the corresponding estimates from NCEP re-analysis than the more complete HadCRUT 3v data. This may be a coincidence. The re-analyses use additional data to fill in the voids – e.g. satellite measurements and predictions based on the laws of physics. Thus, the temperature in areas with no observations is in principle physically consistent with surrounding temperatures and the state of the atmosphere (circulation).

Below is a figure showing a similar comparison between HadCRUT 3v and GISTEMP (from NASA/GISS). The latter provides a more complete representation of the Arctic by taking spatial correlation into account through an extrapolating/interpolating in space. But GISTEMP does not really have a better empirical basis in the Arctic, but the effect from the extrapolation (the filling in of values where there is missing data) gives the recent high Arctic temperatures more weight.

GISS-CRU warming difference over 1996-2004
Figure caption: The 2007 mean temperature anomaly wrt to 1961-90: (upper left) HadCRUT 3V, (upper right) GISTEMP, and (lower) temperature evolution for the Arctic (red=GISTEMP, black = HadCRUT 3v).

A comparison between temperatures over the most recent available 30-year period (1978-2007) shows high temperatures over parts of Russia (Figure below – upper left panel), and the difference between the GISTEMP and HadCRUT 3v shows a good agreement apart from around the Arctic rim and in some maritime sectors (upper right panel). The time evolution of the Northern Hemisphere mean for the two data sets is shown in the lower panel, showing a good agreement over most of the record, but with slightly higher GISTEMP estimates over the last 10 years (the global mean was not shown because my computer didn’t have sufficient memory for the complete analysis, but the two data sets also show similar evolution in e.g. the IPCC AR4).

GISS-CRU mean difference over 1976-2005
Figure caption: (upper left) HadCRUT 3V mean T(2m) anomaly over 1976-2005 (wrt to 1950-1980) ; (upper right) The GISS – HadCRUT 3V difference in mean T(2m) over 1976-2005; and (lower) the Northern Hemisphere mean temperature variations (red=GISTEMP, black=HadCRUT 3v).

Note, the low Arctic sea-ice extent over the last summers are independent evidence of high Arctic temperatures.

The insufficient observational coverage has also been noted by the IPCC AR4 and by Gillett et al. (Nature Geoscience, 2008), who argue that the observed warming in the Arctic and Antarctic are not consistent with internal climate variability and natural forcings alone, but are directly attributable to increased GHG levels.

They also suggested that the polar warming is likely to have discernable impacts on ecology and society (e.g.).

In their study, there are at least 15 grid boxes with valid data (usually representing one measurement) over 1900-2008 period. Furthermore, the only valid observations they used from the Northern Hemisphere were from the Arctic rim, as opposed to in the high Arctic itself. The situation is slightly better for the Antarctic (with one observation near the South Pole). Nevertheless, the title ‘Attribution of polar warming to human influence’ [my emphasis] is a bit misleading. Parts of the high-latitudes yes, polar no.

The attribution study was based on series of 5-yr-mean temperatures and spatial averages of 90 degree sectors (i.e. to four different sectors), where sectors and periods with no valid data were excluded.

There are some caveats with their study: The global climate models (GCMs) do not reproduce the 1930-1940 Arctic warm event very well, and the geographical differences in a limited number of grid-boxes in the observations and the GCMs may have been erased through taking the average value over the 90-degree sectors.

The 1930-1940 Arctic warming was probably not externally forced, but one could also argue that the models do not capture all of the internal variations because few reproduce similar features. Furthermore, the present GCMs have problems reproducing the Arctic sea-ice characteristics (which tends to be too extensive), ocean heat content, and fail to capture the ongoing decrease in Arctic sea-ice area. Most of these problems are seen in the gap with no CRUTEM 3v data, but there are also some uncertainties associated with the lack of data in the Polar regions.

The optimal fingerprint analysis hinges on the assumption that control simulations with the GCMs realistically reproduce the climate noise. I think that the GCMs do a good job for most of the planet, but independent work suggest local problems in the Arctic associated with a misrepresentation of the sea-ice extent. This may not have affected the analysis much, if the problem is limited to the high Arctic. Furthermore, the results suggested a one-to-one correspondence in trends between simulations and observations, but the analysis also gave a regression coefficient of 2-4 for natural forcings. The latter suggests to me that there may be some problems with the analysis or the GCMs.

Thus, this is probably not the final word on the matter. At least, I’m not convinced about the attribution yet. The whole boils down to insufficient amounts of empirical data (i.e. observations), GCM limitations at the high-latitudes, and too large data gaps. But the pronounced changes in the Arctic are consistent with AGW. The irony seems to be that the real world shows signs of more dramatic changes than the GCMs project, especially if you look at the sea-ice extent.

The lack of data in the polar region is a problem, and the ongoing International Polar Year (IPY) campaign is a huge concerted international effort to improve the data. Data is irreplaceable, regardless of the modelling capability, as science requires the theory to be tested against independent empirical data. The re-analyses provide a physically consistent description of the atmosphere – suggesting high temperatures in the Arctic – but we can only be sure about this when we actually have been there and made the real measurements (some can be done by satellites too)

A glimpse into the technical details
More technically, the complicated analysis involved a technique called ‘optimal fingerprinting‘ or ‘optimal detection’, looking for best signal in the noisy data and puts emphasis on regions where the GCMs give most realistic description of the climate variations. Basically, the optimal fingerprint techniques involved linear least-squares regression, which is familiar to many analysts.

The analysis of Gillett et al. involved ‘time-space’ orthogonal empirical functions (EOF) with truncation of 28 (and up to 78 modes for the Arctic, where the maximum truncation was the number of sectors multiplied with the number of 5-yr means – see supplementary material Fig. S3). These come into the equation through the estimation of the noise (covariance matrix), i.e. the internal variations and their magnitude. The clever thing is that they let each EOFs describe a set of 20 maps of 5-year-mean temperatures, thus representing both the spatial features as well as their chronology.

For the mathematically inclined, EOFs are similar to eigenvectors, and are mainly used to prepare data before further analysis. The purpose of using EOFs is often either to (i) compress the information or (ii) to make the data more ‘well-behaved’ (in mathematical terms: orthogonal). While one typically only use a few of the first EOFs, Gillett et al. experimented with just one up to the whole set because they took advantage of their orthogonal properties to allow the calculation of the inverse of the noise co-variance matrix. This is a neat mathematical trick. But this doesn’t help if the GCMs do not provide a good description of the internal variations.

419 Responses to “Mind the Gap!”

  1. 151

    Great article. Something has to be done in order to stop the growing CO2 emission. Im hoping that the COP15 in Copenhagen next year will have a global deal on CO2 reduction.
    to read about how the danes is trying to put a stop to the big co2-emissions visit:

  2. 152
    Chris Colose says:

    rasmus (response to 143)

    The 1900-1940 warming looks global but not as pronounced as the modern warming trend. On the other hand the 1940-70 “flatline” is mostly NH restricted due to aerosols being predominant in the NH at the time. The majority of warming comes over the last few decades– as far as I’m aware the earlier warming involved increased solar, some lack of volcanoes, probably a “dirtier” arctic. GHG’s are responsible for today’s warming.

    #144 PHE

    I would agree that pre-satellite observations of sea ice extent have more uncertainty and are a worthy discussion. Fig 2.6 that rasmus referenced shows temperature, not ice extent (there should be a correlation, but it’s not direct evidence). Notably, as far as we can tell, the earlier warming caused increased melting, the following cooling allowed some regrowth, the later warming is causing more melting, and the future (without change from business as usual) is expected to cause very much larger warming than that achieved so far, and so to cause a lot more melting. Even right now all the best indications suggest warmer arctic temperatures now and less ice in modern times but with enough uncertanty since data is poor back in the early century in that region.

    Comment 138 by Michael on the other hand is hardly worthy of much “thought.” It was regurgetated nonsense.

  3. 153
    Geoff Beacon says:

    Re 146. Thanks again Lawrence, it’s nice to have someone, who knows a bit about the subject, to talk to. But I’m interested in some loud cautionary noises, which might encourage governments to have more robust contingency plans for slowing climate change. Who better to do make the noise than RealClimateScientists. That is unless the scary scenarios have no chance of coming about. I’d be delighted to be told they are just fantasy.

    Contingency plans.

    1. Hair shirts: Stop nearly all flying, buying wine in bottles, most driving, eating meat (beef and lamb particularly), stay colder in the winter, ration power…

    2. Financial incentives: Pay for carbon abatement (e.g. pay to keep forests and farm biochar instead of sheep and cattle). Reward power companies for cutting our energy consumption not increasing it. Subsidise building materials that incorporate carbon and tax those that don’t.

    3. Efficiency improvements etc. These might allow us to keep some semblance of our current lifestyles (c.f. Amery Lovins of the Rocky Mountain Institute). These include cars that weigh a fraction of today’s cars, renewable electricity, light-bulbs that give out light but not much (wasteful) heat.

    4. Geo-engineering. SO2 in the upper atmosphere, iron salts seeding the sea, cloud-making barges and, of course, biochar.


    … even under current UK plans. The UK government is emulating King Canute and legislating for an 80% cut in UK GHG emissions. That puts us on about 2 tonnes CO2e per year each. Let’s set aside one quarter (500kg) for each of: travel, food, household and government. So you have 500kg CO2e for travel.

    You can’t fly much. UK to NY and back is over 2000kg CO2e. So what if you spend your ration on your car? You create about 125 gm CO2e per kilometre (some CO2e added for exploration, drilling, refining and shipping your fuel). Your ration seems to be 4000 kilometres per year. In the UK, I think an average car does about 20,000.

    And the worse news is that building the car will probably have taken more than 5 years of your transport ration.

  4. 154
    Joseph O'Sullivan says:

    Re #144 (PHE)

    I think Gavin and the rest of the contributors to RC do a very good job dealing with contrarian information. They exhibit lots of patience dealing with it.

    Its very easy to get sucked into a noisy and time consuming argument. I’ve done it myself here on RC. Firm responses like Gavin etal’s address the questions for the larger audience while keeping a higher quality of discussion going.

    The end result is RC is a great resource for science that is sorely missing on the internet.

    ReCaptcha “On denistry” I had a root canal done yesterday!

  5. 155
    Rod B says:

    Lawrence (141) I gather Jan 21 is the date because then Obama can [edit] pressure agencies. [edit]

  6. 156
    Jared says:

    #140 Gavin-

    In response to “the satellites showing more sensitivity to ENSO”. I don’t think that is an adequate explanation, if you look at the other strong La Ninas in the satellite era: 1989, 1999, and 2000. GISS always had less than a .055C divergence in each of those years. So what is different about the La Nina of 2008 has caused GISS to show a much larger divergence?

    [Response: That might be worth analysing. Each La Niña/El Niño event has a different structure, and you could look and see whether there is something systematically different last time out. Let me know if you see something…. – gavin]

  7. 157
    Jared says:

    #152 Chris Colose

    I really don’t think there is any real certainty now about aerosols being the primary cause of cooling from 1945-75. That theory was first established before the discovery of ocean cycles like the PDO. As most of us are probably aware, the PDO went into it’s negative cycle around 1945 and then flipped to its positive cycle around 1975. The Pacific being a rather large ocean, this had a very noticable effect on NH climate during this period.

    Seeing as how the 1925-45 warming also came during a +PDO phase, I think it would be rather narrow-minded to dismiss oceanic cycles as a significant part of global climate trends seen over the past 100 years…including the cooling period from 1945-75, and the warming from the late 1970s until recently.

  8. 158
    will says:

    #118 Mike Tabony
    I did not have old-timers I could talk to but I think your anecdotal evidence on warming is a bit exagerated. I did a quick check using Google and it was pretty easy to find pictures of a Frozen James River in Virginia. One from 2004 and the other 2007. See the links below. I’m not sure many of your old-timers are still attempting to walk their horses across the river but the river still seems to be freezing in the winter.

  9. 159
    Mark says:

    Furry Cat Herder, what makes you think that the sun isn’t included in the models?

    El hams as al raisa (I think, “the place where the sun shines not”)?

    See, the problem with the gap is that the denialists don’t want to look at the graph as posted because it doesn’t show what they want to see. So they pick the last 8 years and say, since it is not going up as fast as it was in the previous years to 98, it is going down. And since it’s going down, there’s no AGW.

    Showing them the graph as you do doesn’t change that because they will just ask to see the last 8 years and prove themselves right.

    PS FCH: I take it the sun produces massive amounts of tachyons since the reduction you feel is the result of the quiet period started after warming really took off and if the sunspots cause cooling, then the “it’s cooling” happened years before the new cycle started. So whichever way sunspots are supposed to act, it has to be acting after the effect.

  10. 160
    Mark says:

    Gavin (responding to #138) you forget several things:

    1) He never said he read anything. He didn’t so he can make things up.

    2) He doesn’t know the difference between “not modelling solar effect” and “modelling solar effect isn’t enough” so how do you expect him to know the difference between “here are the uncertainties” and “there are no uncertainties”?

    3) He’s not a scientist, so he’s figuring on what he wants scientists to think. Trying to get him to read what scientists think breaches requirement #1.

  11. 161
    Hank Roberts says:

    Mark, can you be certain he’s not a scientist? Looking in Google Scholar, someone with that name has done science (not in climatology).
    He could be a scientist. Beliefs outside one’s expertise do occur.

  12. 162
    Chris Colose says:

    Jared (156)

    I have yet to hear any adequate reasons why PDO should influence global mean temperatures on decadal timescales. The fact aerosols were rising over this time period (this shows up with known industrialization, ice cores have a record of higher activity, etc); Also, the cooling was hemisphericaly confined which suggests aerosols played at least a good part in it. Natural factors likely played some role–the best fit from Meehl et al 2004’s model comes from natural+anthropogenic factors. But overall the “cooling” was mostly a “flatline” and not very interesting (at least to me!)

  13. 163
    Hank Roberts says:

    PS, Mark, I highly recommend looking up the study described here; some approaches consistenly will not work in presenting information:

  14. 164
    Jared says:


    Yes, that is true, each ENSO event has a unique progression. I did notice that the one other year that had a large divergence between GISS and the satellites was 1998 – which of course was the exceptionally strong El Nino event you referenced before. The 2007-08 La Nina was not nearly as exceptional of an ENSO event.

    Really, the closest comparison to this year would be 1989 – though that one was a bit stronger and peaked a bit earlier, the SSTA progression has been quite similar to 2008. The 1989 La Nina was strong until Feb/March (same as 2008), weakened rapidly to negative neutral by May/June (same as 2008), and then maintained neutral status through the fall (same as 2008).

    However, in 1989, GISS and UAH/RSS agreed much better. And 2000 isn’t a bad ENSO fit to this year either through the early fall…there was also much better agreement that year compared to 2008. So I guess I am still at a loss to understand the major divergence this year.

  15. 165
    Mark says:

    Here’s a highly recommended quote from the BBC Have Your Say section about the cold snap:

    “We can’t possibly have a cold winter – scientists tell us the earth is getting warmer. Apparently there has been so much snow in the Alps they have opened the season two weeks early – but I’m sure the white stuff must all be a figment of the imagination.

    harry portsmouth ”

    The same people who say “you can’t tell it’s global warming just because this year (1998) is the warmest on record” say “This winter is cold! SEE! There’s no such thing as Global Warming!!!!!”.

    The Register does the same sort of guff too. And ban comments that don’t fit their needs for denial or give enough to be misquoted.

    Which is nice.

  16. 166
    Cynic says:

    I’d like to suggest that post number 7 by Mark Fiore be a topic all it’s own on the Realclimate site.

    There are a couple of encouraging signs in the world. Waxman hopefully winning a chairmanship over Dingell, Obama, etc.

    But I personally believe that the people who make decisions in this world are going to think they have other priorities than climate change.

    Even if this isn’t correct, it is what is going to happen. Let’s say that China (or US, doesn’t matter really) curtails growth by using less energy (which means burning less coal). My guess is whoever did it is going to be removed from power, unless it is a full blown North Korea kind of situation.

    The world currently has an economic crisis which pretty much is hitting everyone right now. When you are hungry or tired of being poor, or just facing a decline in living standards you are very likely to disregard an “abstract” (ie the effects won’t hit me in the next couple of years. I have problems NOW.) notion like climate change.

    Basically I believe nothing will be done. I am also someone who believes in the peak oil argument. I think that as we deplete energy resources like petroleum and natural gas we are going to burn more coal (lower quality, more carbon dioxide produced per energy unit produced) in it’s place, as well as burning more coal due to population increase, and more due to desperately poor people who just want the good life too.

    I guess it is … I don’t know what. But what are the consequences, and how quickly will they show up if nothing is done?

    I keep toying with the idea of Cleveland and Detroit. Land is very cheap there now. With the world warming, and the American southwest drying, these places have a lot of attractive features.

    I mean what would the climate of Cleveland be like (rainfall, temperature, winters, etc.) with 600 ppm CO2 in the atmosphere?

    Someplace like Vietnam? Or a dry Med style climate? African Savannah? Will I be watching the Great Lakes recede? What?

    Give me something I can use. Pick the US as a region to describe, tell me the American Southwest is a dry deathtrap with temperatures highs of 130 F in the Summertime. Tell me whether S. Dakota is a desert. What is the Pacific Northwest going to be like? I’ll take care of worrying about the REFKAP’s (Refugees formerly known as Californians)

    Basically I think this site is beating a dead horse. Nothing is going to be done. The only real hope is renewables being able to carry a much bigger part of the load, or nuclear really being viable (there is an awful lot to argue about on this one. But as currently implemented (ie Fuel Cycle, reactor designs) it isn’t going to save the world. And the renewables have an awful long way to go to provide the kind of energy the world is going to demand.

    Throw us cynics a bone. Maybe it is the kind of thinking that got us into this situation, but if you can’t eat it or screw it, it just isn’t useful.

  17. 167
    thingsbreak says:


    As most of us are probably aware, the PDO went into it’s negative cycle around 1945 and then flipped to its positive cycle around 1975. The Pacific being a rather large ocean, this had a very noticable effect on NH climate during this period.

    Seeing as how the 1925-45 warming also came during a +PDO phase, I think it would be rather narrow-minded to dismiss oceanic cycles as a significant part of global climate trends seen over the past 100 years…including the cooling period from 1945-75, and the warming from the late 1970s until recently.

    [recaptcha: UNSOUND it’s]

  18. 168
    will says:

    Based on this study in Nature 2004
    “one needs to go back over 8,000 years in order to find a time when the Sun was, on average, as active as in the last 60 years”. Given that we have experienced a lull in sun activity and temperatures are beginning to cool, are we certain that we are going to be warming in the next 20-30 years?

  19. 169
    Richard says:

    Industrially generated CO2 should logically start reducing as the financial crisis moves from the banks to the industrial sector. For example as the car market and other high energy consuming markets contract a noticeable effect shold be visible on global CO2 concentration. Since CO2 mixes rapidly it would seem reasonable to expect some effects to be come apparent in 2009 (if the recession gradually becomes a depression).

    If the global energy consuming industries continue to contract and there is no corresponding reduction in CO2 this may indicate that the CO2 increase is not necessarily purely due to industrial output.

  20. 170
    Hank Roberts says:

    Will, you’re pointing to Sciencedaily on Solanki.
    Type the name into the Search box at the top of the page for discussion since that 2004 article came out. It’s well covered here long ago.

  21. 171
    Hank Roberts says:

    Richard, nobody has ever suggested that CO2 increase is necessarily purely due to industrial output. Too many adjectives.

    You need to remove the annual cycle to clearly see, for example, the wiggle as the USSR fell apart starting around 1989:

  22. 172
    Mark says:

    Hnk, #161. I could maybe (maybe) take him as a scientist if he’d even bothered to read anything to do with the science of climatology (even if it was only the summary report of the IPCC) before writing that message of inanity.

    If you don’t even bother with basic reading behind the subject before telling people what they’re doing wrong, you ain’t no scientist. You may have a BSc, but you ain’t a scientist.

  23. 173
    Jared says:

    #167 Thingsbreak

    I’m not saying that the PDO is wholly responsible for longterm temperature trends, not at all. Just that it is a major influence on decadal trends. Those who argue that the 1945-75 cool/flat-line period was due to aerosols are really not looking at all of the evidence available.

  24. 174
    Jared says:

    #162 Chris

    Right, the “flat-lining” global temperatures were due to a slightly cooling NH and a basically flat SH during the 1945-75 period. But if you think about the PDO, that makes perfect sense: Pacific Decadal Ocscillation. The PDO phases occur in the North Pacific, and therefore mainly effect the northern hemisphere.

    The correlation of NH temp trends with the PDO (and to a lesser extent the AMO in the Atlantic) is simply too great to ignore.

    [Response: Actually, just the opposite–its too small to be meaningful (by design, in fact). The formal definition of the PDO involves subtracting off the global mean SST from the North Pacific SST field and defining the index as the residual pattern. The AMO is typically defined by taking the leading non-ENSO EOF of the North Atlantic SST field, subtracting the warming trend, and defining the index as the residual (though this is slightly different from the original definition of the AMO by Tom Delworth and myself). More recent work by Knight et al (which I was also involved in) finds that the maximum peak-to-peak projection of the AMO onto global or Northern Hemisphere mean SST is only a tiny fraction (on the order of 0.1C) of the 20th century global mean warming trend. In short, these indices define the residual, ostensibly oscillatory regional temperature signals after the long-term, large-scale global warming signal has been subtracted off! The AMO and PDO are defined precisely so that they are largely orthogonal to global warming, and it is simply invalid to view them as contributors to it. Its unfortunate that these basic aspects of how the AMO and PDO are actually defined are so often misunderstood or, worse, intentionally misrepresented by climate change contrarians (in their effort to make a disingenuous case for global warming being due to ‘natural oscillations’ in the climate system). -mike]

  25. 175
    Stuart Harmon says:

    [Response: But you don’t seem to realise that previous observations are in fact built in to the statements about sea ice. Old ice charts from the Danes, UK, Norway etc. go into the HadISST product for instance. The ice was more extensive in the past, and in fact there are plenty of old observations of extensive land fast ice back in the 18th Century that simply doesn’t exist any more. That is not being disengenuous. What is disengenuous is quoting a 1922 report without putting it context to imply that nothing is different now – you could not be more wrong. – gavin]

    Dear Gavin

    It is not a quetion of whether I am wrong or you are right the simple fact is that the empirical evidence does not support the hypothesis that man made CO2 emissions will cause dangerous levels of global warming.

    Ice core data shows that temperature rises precede increases in CO2 in the atmosphere. But of course on a BBC web site you said this was due to the earth wobbling.

    I am afraid that you have lost the argument and one of the reasons for this is because you are wedded to a belief system.

    [Response: The irony of your response, I have no doubt, is completely lost on you, but hopefully is apparent to all other readers. – gavin]

    The climate always changes the temperature rise in the last century was not unusual.

    Take care

  26. 176
    Mark says:

    “Ice core data shows that temperature rises precede increases in CO2 in the atmosphere. But of course on a BBC web site you said this was due to the earth wobbling.”

    OK, Stu.

    Where’s the 600 year old increase in temperatures to take us to 50% more CO2 as per ice core record. Not the recent ones, 600 years ago, it would have raised X degrees C by 100 years ago, what X does the ice core data give?

    You should know because you seem to think yourself an expert.

    Now, when you’ve done that, please let us know how the isotopic signature changed 33% of the carbon out in our atmosphere.

    Now, when you’ve done that, please let us know where the 17trillion kilos of carbon each year we put out goes.

    I am afraid you may have lost the argument, one of the reasons being you’re wedded to a belief system.

    The climate changes of the past are insufficient to the changes of the future. We have a mechanism that explains the discrepancies but that involves fossil fuel combustion on a gigantic world-wide scale. And the only mechanism is human activity.

    Take care your brain doesn’t freeze up.

  27. 177
    Dave Andrews says:


    The AMO and PDO are defined precisely so that they are largely orthogonal to global warming, and it is simply invalid to view them as contributors to it.

    What exactly do you mean by “defined”? Is that how the PDO and AMO are used in the GCMs?

    [Response: In control simulations with GCMs such as used in Delworth and Mann (2000) and Knight et al (2005) which I linked above, there is no need to separate the internal multidecadal variability from the forced long-term trend, because there is no change in radiative forcing, and thus no forced (including anthropogenic) large-scale trend to contaminate the estimate of internal multidecadal variability. No such luck in the real world, where both are present. In that case, one needs to use some technique for separating the multidecadal variability from the long-term trend. In many papers, this is simply done by subtracting off a linear trend and defining the residual as e.g. the “AMO”. I don’t particularly like that approach, because the radiatively forced temperature trend is extremely unlikely to be linear in time [this is an issue we discussed in Mann and Emanuel (2006)]. I prefer frequency-domain signal detection techniques such as the “MTM-SVD” technique (for obvious reasons) which was employed by both Delworth and Mann (2000) and Knight et al (2005). -mike]

    Surely you must recognise that they at least have some effect on temperatures on a regional basis and that this therefore in turn affects global temperature as measured by GISS etc?

    [Response: As I mentioned earlier, we actually looked at the global temperature projection of the internal “AMO” signal present in control simulations of the GFDL (Delworth and Mann, 2000) and UK HadCM3 (Knight et al, 2005) coupled models. The peak-to-peak impact of the AMO on global mean temperature is in both cases a very small fraction of a degree C (at most, about 0.1C), and dwarfed by e.g. the 20th anthropogenic warming signal. -mike]

  28. 178
    Richard Ordway says:

    175 Stuart. “I am afraid that you have lost the argument and one of the reasons for this is because you are wedded to a belief system.”

    Well, I guess I too will throw in some cryptic statements.

    By definition, Gavin falls a little short of “being wedded to a belief system.” Gavin does and is currently doing lots of peer-reviewed papers and so can be called a “mainstream scientist.”

    Therefore, he is a skeptic.

    According to Wiki,: “In a more restricted sense, scientist refers to individuals who use the scientific method.[1]”

    Also Wiki goes on to state that “scientific researchers propose hypotheses as explanations of phenomena, and design experimental studies to test these hypotheses. These steps must be repeatable in order to dependably predict any future results. Theories that encompass wider domains of inquiry may bind many hypotheses together in a coherent structure.”

    Hmmm, sounds pretty straight forward to me. In other words, Gavin and other mainstream scientists’s data has been openly tested over time and found to be so strong (and has not fallen apart under fierce experimental attacks) that Gavin is saying things like global warming and its current causes (are more or less facts) such that other mainstream scientists don’t challenge what he says.

    This means, sir, that I highly question whether your comments meet these same stringent requirements. Ie., Gavin cannot be wedded to a belief system if this system is open to being tested and changed. He is a skeptic (willing to test any conclusion)or he cannot be called a mainstream scientist.

  29. 179
    Maya says:

    “Basically I think this site is beating a dead horse. Nothing is going to be done.”

    You may be right, but not having this site, not voicing the arguments and facts, not agitating with the policymakers and politicians … isn’t going to accomplish anything. So, we (everyone who talks about AGW, posts about it, researches it, writes letters about it, convinces a neighbor, anything) have to keep trying. The apathetic alternative is not acceptable, imho.

    It’s hard to be optimistic.

  30. 180
    Jared says:


    Sure, the PDO numbers are adjusted for SST changes. However, there is no disputing their cyclical nature, and their subsequent relationship to ENSO…which has a very substantiated effect on global temperatures. Therefore, to say that the PDO and AMO have very little effect on global temperatures when there is ample evidence that oceanic thermocline cycles do indeed effect climate, is just not true.

    Again, I have failed to see evidence of a better and more consistent explanation for 20th century decadal climate variation. Again, I am not saying the PDO or AMO are responsible for global warming trends. Simply that these natural cycles influence climate trends over decadal time frames.

    [Response: I think you meant ‘Mike’? See my responses to comment #177 above by Dave Andrews. -mike]

  31. 181
    Lawrence Brown says:

    Re #155
    “Lawrence (141) I gather Jan 21 is the date because then Obama can [edit] pressure agencies. [edit]”

    Right on Rod. That’s the date(when the new administration takes office) that as far as I’m concerned, our long national and global nightmare will end in regard to the U.S. energy and climate change policy.
    Even the standard bearer from Bush’s own party, John McCain, said that as far as climate change is concerned,Bush is “missing in action”.

  32. 182
    Hank Roberts says:

    Pertains to the topic:

    Public Radio International, today:

    (Take out the space after the slashes, trying to work around a failure to post this)


    download link: http://

    Denial near and far (9:45)
    November 21, 2008
    About one in five Americans still doubt that the Earth is warming. Is this healthy skepticism or denial? The World’s Jason Margolis reports on cultural denial around the globe.

    Key point: don’t use the label ‘denialist’ — it’s used and emphasized by skeptics who want to position themselves as victims. It is not useful for someone unconvinced to that word. Emphasize this. Don’t use that word. Speak to the science, not to saying things about people who you consider wrong. That would include not getting sucked into namecalling and labeling even when “they did it first” eh?

    Excellent nine minute audio about how people find this subject very hard.

    Related to the link I posted earlier, a story summarizing research about what people do and don’t hear, recall and believe, this one:

    Stay with the science, is the message. Repetition convinces people no matter the source, and they don’t remember which sources they trust.

    Repeating bogus claims _even_to_refute_them_ makes people remember them better. It’s counterproductive.

    Teach people how to learn facts, so they can convince themselves about the science.

    It ain’t easy. But we have the Fermi Paradox to motivate us.

  33. 183
    Rod B says:

    re my 155: Shoot! I know what was edited was off topic and off focus, but it was the good stuff! :-P

  34. 184
    pete best says:

    Re #182, only one in five, cool, [edit – no partisan politics]

    Maybe Barack Obama will manage to use his significance in th worlds standing to deliver a beautifully crafted energy strategy for the world where producing CO2 becomes expensive and hence helps deliver the grand plan for sustainable energy source provision and efficiency gains (especially seeing as how the US car companies are in trouble financially) that we need.

    I still doubt that the world will reduce emissions with out the historic polluters the west paying for the costs of this new technology for the world which is unlikely.

  35. 185
    Ray Ladbury says:

    Hank, I’m afraid I don’t agree that calling those in denial about climate change denialists is counterproductive. It accurately reflects their views. The confidently come into public debate and assert the opposite of what all the peer-reviewed research says–even in forums like this, where people are quite familiar with the peer-reviewed research. This can only be explained by 4 hypotheses: 1)They are ignorant of the research and still confident of their fixed ideas. In this case, would ignoramuses be less pejorative? 2)They assert the opposite of the research hoping to convince the uneducated among the public. I think denialist is less pejorative and more charitable than “liar,” don’t you? 3)They are aware of the research, but deny its existence or correctness. What else can you call someone like this but a denialist. 4)They are familiar with the research and do not understand it, but still confidently assert that those whose job it is to understand it are wrong? I agree that denialist does not capture these attitudes 100% accurately, but it’s a whole helluva lot more polite than more accurate labels.

    On the whole, denialist comes closest to labeling the entire looney fringe that rejects good science. No matter what label we came up with, they would claim persecution, and I refuse to drag skepticism through the mud by applying the term to these people.

  36. 186
    Mark says:

    “Teach people how to learn facts, so they can convince themselves about the science.”

    Hank, there’s your problem right there.

    The denialists DO NOT WANT AGW to be true. The fence-sitters don’t see a need to find out and since there are two sides arguing, there’s “no consensus” on the deal “so wait until they sort it out”.

    When their homes are permanently flooded, THEN they’ll educate themselves but then it’s too late.

    It’s a war here and you don’t win wars by educating the neutral powers.

  37. 187
    Lawrence Coleman says:

    Re:186 Mark. Dont be frustrated over what the little minnows in the fish pond say. Most govs of the world know that they have to take the information in relation to CC from the most reliable informed sources eg. the members of the IPCC to name but the best. Now that very soon you wont be burdoned and paralysed by a president with his head firmly in the sand bucket, this crucial message will be taken all over america and the world in unison and the denialists pathetic voices will be silenced once and for all. Then and only then can ALL our respective energies be channeled into fighting this epic battle.

  38. 188
    Richard says:

    Re #171 sorry you found the adjectives so offensive

    “Richard, nobody has ever suggested that CO2 increase is necessarily purely due to industrial output. ”

    Does that mean you disagree with AGW? So Are there posts in this blog telling people that they should keep their gas guzzlers because the CO2 increase isn’t due to industrial output?

    If the collapse of the soviet union made a wiggle, a worldwide crisis might have a more significant effect? (the average energy consumption of a russian is not really comparable to the average energy consumption of an american).

    In any case if the financial crisis has no impact then maybe people switching their lights off won’t have much effect either?

    re #172 PhD + 10 years post doctoral research in turbulence simulation

  39. 189
    Lawrence Coleman says:

    153: Geoff Beacon. “Who better to do make the noise than RealClimateScientists. That is unless the scary scenarios have no chance of coming about. I’d be delighted to be told they are just fantasy.”
    These scary scenarios will happen just as the sun makes it’s celestial appearence every morning and sooner than predicted. You make your bed – you sleep in it! That’s why govs must think of ways that are win-win. To capture CO2, cut emissions by 90% and benefit the economy. It’s obvious than when your budget is cut by 2/3 like most world economies are that you need different ways rather than throwing copius billions of dollars into infrastructure to mitigate CO2(nobody can currently afford it.) Agressive carbon tax must employed and legislation must be incorporated that those companies do not pass on 1c of their carbon penalties to the consumer. Sure many precarious companies will go to the wall..but that’s the stance we have to take. What I do know is that if everyone doesn’t make a 100% effort NOW and keep that effort up for many decades to come there is no sustainable future for our planet and I cant make it clearer than that.

  40. 190
    Lawrence Brown says:

    Re:#175 Stuart says:
    “The climate always changes the temperature rise in the last century was not unusual.”

    And people are always getting sick. This doesn’t mean we should give up on treating illness.

    Why does the climate change?(everyone agrees that climate isn’t static). It’s due to forcings from various sources
    e.g., solar flux, orbital changes, value of albedo(reflectivity) and chemical composition of the atmosphere.
    Since the dawn of the industrial age, gases such as carbon dioxide, that allow high energy sunlight in and trap
    low infra-red energy reflected by the surface, have increased. CO2 is about 40 percent higher at about 385 ppmv,than
    it was 250 years ago, due to the burning of fossil fuels by man (and woman). This is the primary forcing driving climate
    change today. I know this is all basic, but it bears repeating.

    There’s a close correlation between the amount of CO2 in the atmosphere and Earth’s average temperature. Sometime
    one lags and the other leads, and vice versa. In the geologic past, temperature rises have occurred before atmospheric
    increases of CO2,but that’s not the case in the present.

  41. 191
    Nick Gotts says:

    Land use change is a big contributor to rising CO2 levels: when forest is cut down or grassland is ploughed up, or peat is cut or dries out, CO2 is released. I don’t have exact figures to hand, but these factors account for a significant percentage of recent increases. They are likely to persist even in an economic downturn.

  42. 192
    Hank Roberts says:

    Mark, did you read the survey result at the PRI page and listen to the audio program? If it were a war it would be won, with those numbers convinced. The remaining 20 percent are a problem — but not because they’re an enemy. Read some of David Brin on the need for science education and on politics, please, after you listen to the PRI piece and read the studies discussed in the news article.

    The point is — there’s good science about climate, and there’s good science about how people do and don’t learn and change beliefs.

    I’m urging you to attend to the science about the latter. It’s not easy, it’s not intuitive, it’s not like playing war. It’s not been done anywhere before now except, very slowly, with teaching evolution — where the right approach has been followed.

    Read the science about how people change what they believe. Look at where it’s worked.

    “… not necessarily purely due to industrial output” and your followup 188 “Does that mean you disagree with AGW” is talking point stuff.

    Are you trying for irony? Or asking for debate on those terms?

    Try asking a science question! One of the real scientists here may have answered it — if so I may be able to help you find it.

    If you’ve read the Start Here and sidebar links already, you’ll ask one they haven’t answered — and that’s a very good way to start — they’ll tell you it’s a good question and delve into it and we’ll all learn a bit more.

  43. 193
    Anthony Leonard says:

    Has there been a year to year measurement of the total heat content of both the ocean and the atmosphere? If the atmospheric variation is due to ocean circulation variability then presumably the sum of the two would have less variability. However, I would guess that the ocean heat content measurement is not accurate enough on a year to year basis to remove this variability, but it sure would be nice to help explain in a simple manner the atmospheric variability.

  44. 194
    Mark says:

    No, Richard (#187), that doesn’t mean AGW is wrong. It means that not all CO2 is due to human activity.

    By denying AGW are you saying that we are doing NOTHING to the earth to change it???

  45. 195
  46. 196
    Rod B says:

    of which Lawrence is evidently wildly in favor of…

  47. 197
    jcbmack says:

    It is human nature… who wants to admit that our own efforts, our amazing technology, our ingenuity has led to a warming phenomenon can lead to catastrophe if we do not make major changes, spend an enormous amount of money and so forth. Then those outside of science or at least climatology say: you do not have an exact charney sensitivity value, so what are you getting concerned or “alarmed, “about?” Then there is the issue of various physicists, chemists and so forth who have little understanding of weather and/or climate and want it all neatly quantified or else it does not exist. Industry runs this capitalistic society, from free trade, free market, to government support from special interest groups. The funny thing is we still have time to make drastic changes and make long standing improvements.

    For those of us who understand the science know that we have areas of great uncertainty and have a responsibility to explain the issues and bring clarity to these matters, but as we have seen in the news media, in the colleges and in this blog, this is a daunting task to say the least. I have serious problems with carbon cap and trade, it may not work out too well, especially since with enough money people can go over emission standards and with enough money and power, there is plenty of scandal and corruption on the horizon.

  48. 198
    Dave Andrews says:


    What I do know is that if everyone doesn’t make a 100% effort NOW and keep that effort up for many decades to come there is no sustainable future for our planet and I cant make it clearer than that.

    And exactly how do you ‘KNOW’ that Laurence?

  49. 199

    “It’s a war here and you don’t win wars by educating the neutral powers.” Actually, I think this is called diplomacy and has won a lot of wars over the centuries! :)

    I think Hank makes some really good points. In particular, I think that the idea of repeating the truth, not the bogus arguments–is excellent. (In the forum I “patrol”, I always emphasize the *known* science (easy, since the #1 denialist meme at the moment in those fora seems to be “there’s no empirical evidence for AGW,” which is a perfect intro to “Well, actually the IPCC bibliography runs to thousands of peer-reviewed scientific papers, etc.”)

    Obviously, I don’t think the “denialist” label is necessarily bad–like Ray, I believe it to be accurate (largely.) But it needs to be applied sparingly and carefully, most preferably in the third, as opposed to second, person.

    I don’t think there is a downside to using it carefully, because those to whom it does apply are, by definition, not susceptible to education in any reasonable timeframe. However, one ought to be very careful *not* to apply it to skeptics, as they are the folks you most would like to persuade, and “you don’t catch flies with vinegar.” For the folks who are not yet convinced one way or another, I think that the “denialist” tag may help them to see what is going on–that in fact, a good number of the anti-reality bloggers are just flatly unwilling to consider the evidence.

    As to how the struggle is going, I note that there are lots of “denialist” voices ready to jump in at any point, but that the “AGW consensus” voices get a lot more recommendations.

  50. 200
    simon abingdon says:

    Hank #182 “we have the Fermi Paradox to motivate us”. Fermi’s “where are they?” was a clincher. AGW is not quite there –
    Ray #185 Also 5) The Sun and H2O. More research needed.