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Comments 125651 to 125700:

  1. 1998 DIY Statistics
    "Here is the IPCC projections, circa 2001. They were wrong. " Why IPCC 2001 rather than AR4? Another form of cherry picking? The temperature record falls within the two-sigma error bars of the ensemble projections in AR4. I imagine a similar exercise performed on the earlier projections would show a similar result, but Real Science tends to look at recent results rather than focus on the past ...
  2. 1998 DIY Statistics
    nofreewind: I'm not convinced by your politics argument. If something is wrong mathematically then it's wrong regardless of whether you believe in communism, free markets or pastafarianism. As far as I can tell, when a function has periodic components in it (eg assume that temperature is affected by the Sun's output), looking at a single trend over periods similar to the periods of those components and making absolute conclusions about longer trends is simply wrong. Not bad, or communist, just plain wrong.
  3. What ended the Little Ice Age?
    Re 3 and 4 - I had tried to read Svalgaard too or at least his comments on his work on another blog. If he is right (little solar variation in the last 165 years)and Riccardo is right that climate cannot be so very highly sensitive it leaves me still scratching my head as to what ended the LIA. I note John has said on on a different thread that he was working on a post on ice age/inter-glacial mechanisms.
  4. 1998 DIY Statistics
    nofreewind, oh yes, i see, but unfortunately now global warming has started again at the incredible pace of more the 20 °C/century!!! Pretty scaring, isn't it? Or maybe we (me and you) are missing something?
  5. 1998 DIY Statistics
    Nofreewind, it seems that you haven't got the main point here: In order to find _reliable_ trends as fast as possible, you have to sort out as much as possible of short time oscillations, special events like volcanoes etc. That's what this post is about. "It hasn't warmed sincce 1998" is a typical example of an unreliable trend observation. 1998 was a very special year, and when we are talking about trends, like "it has/hasn't warmed", we are making statements about what the typical situation is. I don't think you have looked very closely into the arctic ice data. That "enormous recovery" you talk about, led, for example, to Nov 2009 ice levels being lowest in several decades, practically the same as 2007, and, rank-wise, we are at about the same level right now. If we had been back to the situation around 2000, we would have been more safe in talking about "recovery" from the 2005-2008 average situation, but we aren't. Also, the September 2007 arctic ice extent is about as untypical as the 1998 global temperature anomaly, so that doesn't in any way establish an ice level to "recover" from.
  6. 1998 DIY Statistics
    This post was started with the statement "It hasn’t warmed since 1998" is still a very popular argument." Then the author began to obtusely deconstruct that statement using all type of complicated data not related to temperature over a much longer period than the past 12 years. I show a few simple graphs to prove the point. Here are all four graphs, it hasn't warmed since 1998, don't you think that is something to consider? Here is the IPCC projections, circa 2001. They were wrong. Marcus, what do sunspots have to do with the topic of this post? Where I hang out with my skeptic pals, sunspots are just another theory to consider, certainly their seems to be some correlation, (cycle length maybe, the Minimums had none etc), but there are diversions it seems. Give it 10 years! "willing dupes of the fossil fuel indusry". HILARIOUS! How many miles of driving using gasoline have you been "duped" into to. How do you heat your home? Why is your electricity so cheap(not oil but coal). Maybe that would I suggest you junk your vehicle and use wood to heat your house, and coal(on to wind), let's not get into that on this topic. Anyone here who believes that big oil has had anything but minuscule influence on this scientific debate is being deceived. Do you want to know about money, read this. , i'll show you the money! Glaciers melting - they have been melting since 1850, don't you know. Arctic Ice - The past two years there has been an enormous recovery from the 2007 September low. And I just read a warmer arctic scientist state he expects further recovery this year. Antartica, at least as far as sea ice goes, no strong trend, except maybe slightly up. Of course there are all kinds of measurements going on in Antartica.
  7. 1998 DIY Statistics
    I tend to agree Ken. Looking to use a single data point to invalidate 30-60 years worth of warming really does highlight the desperation of the Fossil Fuel Industry & its willing dupes (apparently these dupes would rather stuff an extra $1000 per year in the pockets of energy generators than just insulate their homes a bit better?!?!) Oh & I concur with you too RSVP. Temperature alone isn't the only thing that leaves me convinced of global warming, it's the massive shift in rainfall patterns, the retreat of glacial, Arctic & Antarctic ice & a host of other factors that tell me the planet has been warming the last 30 years *at least*!
  8. Sea level rise is exaggerated
    Ken in Oz, as far as i can remember, sediment deposition is historically of the order of a few GTons, or a percent of current ice sheet loss. Negligible. Also, the sedimentation rate is on the decline due to the more and more dams that are bilt. I'd like to see where your friends got the numbers that explain sea level rise with sedimentation, i never heard about it.
  9. Sea level rise is exaggerated
    I got into an argument about sea level rise as an indicator of climate change and was told that all recent rise could be attributed to increased sedimentation rates. Whilst I expressed doubts that, given the global ocean surface area, it could affect overall sea levels that much I had to concede that a lot of river mouths and bays are being affected by both silt from erosion and from deliberate infilling to create waterfront building sites. Locally both can be quite extensive. I have struggled to find quantification of human induced sedimentation and infilling; if anyone can link to something that a layperson such as myself can view and provide some perspective on rates relative to sea level rise I would appreciate it. Thanks, Ken.
  10. 1998 DIY Statistics
    I think that a hot spike in a warming trend as the foundation for arguments the world is cooling just indicates how weak the case for "cooling" is.
  11. 1998 DIY Statistics
    What is also intriguing, though, is how the RSS data shows warming (I hesitate to use the word "trend") of 0.04 degrees per year between 2000-2005 (with an R^2 of 0.434-still not great, but better than 0.0027), which is nearly identical to the GISS value of +0.037 degrees per year over that same time period. These nearly identical warming rates can even be extended as far as 2000-2007 (+0.021 degrees per year for RSS vs +0.025 degrees per year for GISS). Its only in the last two years that the RSS & GISS numbers have really split apart, with the GISS anomaly showing a fall from +0.57 to +0.44 back up to +0.58, & the RSS anomaly showing a drop from 0.308 to 0.09 to 0.26. This is intriguing when you consider what a massive effect just 2 data points can have on such a small data set, & it makes me wonder which are the *correct* data points!
  12. 1998 DIY Statistics
    RSVP, good point. I happen to comment on this problem a lot of times with friends. It appears that people more easily grasp temperature than other often more important effects. I think this is because we all are directly affected by temperature and we have a feeling of it; it's a direct measurement as opposed to indirect measurements such as sea level rise, tree line shift, etc.
  13. 1998 DIY Statistics
    nofreewind, use whatever data set you like but do not be fooled by short term trends, they are statistically meaningless. Based on what you claim that UAH is superior to HadCRU? It's worth recall that surface air temperature data set (GISS, HadCRU, etc.) are not the same as lower troposphere dataset (UAH, RSS). They measure similar but different things, you should not expect to get exactly the same results. Each has its own problems and strengths, their overall agreement is reassuring of the similarity but your sort of conclusive claim is totally unsupported.
  14. 1998 DIY Statistics
    It is curious that the level of mercury in a glass tube seems to be more relevant to decision makers than the actual measurable effects of global warming (i.e., sea level rise, sizes of glaciers, water supplies, etc.) Just as the Earth is a giant magnet, it is also a giant thermometer; you just have to know how to read it.
  15. 1998 DIY Statistics
    nofreewind: Such a short time period is 'wrong' if you assume that things like the Sun affect climate. If the Sun affects climate, then there is a cycle in heat flow with a period of 11 years (same time as the solar cycle). The entire point of my post is that if you take a trend over 1 cycle or less (in fact, you can even do the same with longer periods too), then you get spurious 'trends' that say nothing about greenhouse gases or longer trends, because they're dominated by the short term one. Eg a 1 year trend would be dominated by summer/winter, a 24hr one by day/night. You can get big positive or big negative trends from cycles that have no real trend if you pick your starting period well enough. Eg the linear regression of the cycle Sin(x) in the period [0, 2pi] is negative: http://www.4shared.com/file/184278813/5069ef42/SineNeg.html If you took the trend in the period [-pi, pi] then you'd get an equal and opposite positive trend. However, the 'real' trend is zero. The 'it's cooling' types tend to rely on tricks like this.
  16. 1998 DIY Statistics
    yocta, not sure i understand what you're asking for. If you are curious about how the average absolute climatology is obtained I'd suggest this review by Jones et al.; in section 6 you'll find how they do. This is the "HadCRU method", details vary between research centers.
  17. It's the sun
    Another point. Even with historic low sunspot numbers, global temperatures have still remained above +0.5 degrees over the 1951-1980 mean for the last decade. What happens if we see a sudden surge in sunspot numbers over the coming 22-33 years? Will we see an increase in the rate of warming-per decade-to as much as +0.3 to +0.4 degrees per decade? Its uncertainties like this (& the positive feedbacks of CO2 release from oceans & increased levels of water vapor) which makes me think we should engage in the precautionary principle-namely to immediately begin making sensible changes in our generation & use of electricity to reduce the CO2 emissions associated with our economies (not by reducing GDP, but by reducing both the KW/$ GDP & the tCO2e/$ of GDP.)
  18. 1934 - hottest year on record
    Also, if you look at the US-only graph, you see that after peaking in the 1930's & 1940's, temperatures fall off again (in line with the rapid rise in average sunspot numbers, followed by a sudden dip), but then start to rise again quite quickly-in spite of the fact that average sunspot numbers haven't risen again since the 1950's. Nor do average US temperatures show any sign of falling-as they did in the 1940's!
  19. Temp record is unreliable
    What galls me is this-in spite of the fact that Dr Roy Spencer (of University of Alabama, Huntsville) has been shown that his adjustment for diurnal variations is in error, as far back as 2005, he still persists in using this method, which generates a long-term trend of +0.035 per decade lower than what is should be. If this error is accounted for, the long-term trend for UAH satellite data is around +0.2 degrees per decade (the same order of magnitude as RSS, which was around +0.23 degrees per decade). What's interesting is that *both* of the satellite data-sets give values which are *higher than for surface-based measurements (+0.187 degrees per decade). Another point is this, why do skeptics refuse to pillory Dr Spencer (a skeptic) for his errors, yet are quick to attack any apparent errors made by climatologists with CRU or GISS? That smacks of hypocrisy to me!
  20. 1998 DIY Statistics
    Oh, & my point is further highlighted by the fact that the R^2 value for the trend-line is a mere 0.0027, i.e. too small a correlation to signify a trend.
  21. 1998 DIY Statistics
    So I've been over the RSS data &-though I still say its too short a time period to show concrete trends either way-I come out with a weak warming trend between 2000-2010 (around +0.02 degrees for the decade), in spite of a massive drop in sunspot numbers over that time. Which just reaffirms the strong role of both the sun & GHG's in global warming.
  22. 1998 DIY Statistics
    Nofreewind, what is of particular interest is in plotting sunspot numbers for 1997-2010: http://www.woodfortrees.org/plot/sidc-ssn/from:1997/plot/sidc-ssn/from:1997/trend which shows a massive downward trend in sunspot numbers over the 13 year period(from 100 to almost 0 from 1997-2010). Yet over that same time period, average global temperatures still manage to increase-even in spite of the El Nino event of 1998.
  23. It hasn't warmed since 1998
    Mizimi & others seem to not understand the concept of the Energy Balance. Average Global Mean temperatures for all of 2000-2009 is +0.512, which is a full +0.18 degrees greater than the period of 1990-1999. This is in spite of the fact that the 1990's were dominated by rising sunspot numbers, wheras the current decade has been dominated by record low sunspot numbers (0 for almost the entirety of 2005-2009). Not only that, but the data shows that the rate of warming-per decade-is *accelerating*, not *decelerating*. Lastly, its all very well saying that Global Mean Temperatures will *only* rise by about 2 degrees over the next century (assuming no accelerating in the warming trend), but that is a GLOBAL MEAN. Actual temperature differentiations will be *much*, *much* higher at different parts of the year & at different points of the planet. Winter temperatures might only increase by an average of +0.1 to +0.5 degrees, wheras summer temperatures might increase by an average of 3 to 4 degrees-or more. Some parts of the globe may see a much sharper increase in mean temperatures-& see an increase in heat related disasters. Australia has had 3 record heat waves in the space of only a year, what can they expect in 10 to 20 years time? Also, I'd like to remind you that at least 2 civilizations were wiped out due to a total increase in global mean temperatures of only +0.6 degrees-over the space of almost 600 years. Tell the Anasazi & the Khmer Empire how unimpressed you are by a *mere* 1.8 degree increase in global mean temperatures over the next 100 years, Mizimi. Oh, thats right, you CAN'T because they got wiped out! Seriously, try quoting science instead of regurgitating fossil-fuel industry propaganda, I might then start taking you a little more seriously.
  24. 1998 DIY Statistics
    Hope you guys can tolerate another grade school comment from me, but why not just plot 1938-1979 CRU then switch to UAH because CRU was the best we had until satellites. So there was basically no warming from 1938 to 1997, then we had an enormous step up during the El Nino and we have been wallowing in such since. Very similar to what happened to Alaska with switch of PDO in 1997.
  25. 1998 DIY Statistics
    Excuse me fellas, the above is way over my head. But what is so wrong about simply plotting the 1997-2010 RSS? Or if I must, 1997-2010 CRU?
  26. It hasn't warmed since 1998
    Actually, Mizimi, when you graph the numbers, & draw a trendline, you see the rate of change for 1910-1944 was +0.013 degrees per year, wheras the rate of change for 1964-2005 was +0.016 degrees per year. So this 2nd warming period has been faster than the first one-even though average solar activity during the 2nd warming period has remained unchanged.
  27. Temp record is unreliable
    Mizimi, I have to tell you that your claims regarding the Siberian stations is just plain wrong. If you can provide *proof* of this wild allegation, I'd be happy to entertain it though. As for your claim regarding the satellite data post-2002. Even if what you said was true, 2003-2009 represents too small a sample group to be of any real benefit for determining trends-especially when that period is dominated by abnormally low sunspot numbers. That said, if we look at temperatures from AMSU-A for 1st July, we see that 2003 was -14.42, 2004 was -14.19, 2005 was -14.13, 2006 was -13.94, 2007 was -13.86, 2008 was -14.39 then 2009 was -14.11. This is only a single date, of course, but a look through the entire year shows that, if anything, the trend has been towards *warming* between 2003-2009, not cooling as you claim. As I said, though, picking on these dates-to prove either case-is the worst kind of cherry picking.
  28. Temp record is unreliable
    WA. 1951-1980 was not the *coldest stretch in a century*. The 30-year average of 1901-1930 was a good .24 degrees *colder* than 1951-1980-& is by far the coldest 30 years of the the 20th century. 1931-1960 average is almost identical to 1951-1980, & the 1961-1990 average is slightly warmer than either 1931-1960 or 1951-1980, so I don't see why you think GISS is in error for using this period as a base-line. The satellite data is from 1979-2000 because 1979 represents the start of the satellite measurement period.
  29. It's cooling
    selti, you are wrong about the IPCC projections being disproved. See Comparing IPCC projections to observations. If that's not detailed enough for you, click on the link that's in that post, to Tamino's related post.
  30. Temp record is unreliable
    Wondering Aloud, would Energy & Environment be the same "journal" that published that awful "paper" by Beck-the one claiming that, based on measurements of the day, CO2 levels in the 19th century were higher than in the 20th century? When you look at the results used by Beck, you see they have *massive* margins of error (around +/-200ppm) because most of the samplings were taken in urban environments, were measured without internal controls &/or were measured with equipment with sensitivities 10-100 times worse than modern equipment. Yet E&E still accepted this paper, even when no other respectable journal would touch it, because it fit into their ideological agenda. I suspect the same is true with their "analysis" of monitoring stations.
  31. 1998 DIY Statistics
    Hey MarkR, great post. As I said in posts #4 & #5, I've tried plotting the rate of change in average global temperatures myself, & have come up with a value of +0.108 degrees per decade for 1949-2009, & +0.163 degrees per decade for 1979-2009 (both with greater than 70% correlation). Now I wanted to do the same thing with RSS but, when I downloaded the dataset, I confess the whole thing looked like complete gibberish! Could you quickly explain how I can make the RSS data more....legible? Thanks in advance.
  32. 1998 DIY Statistics
    Ah coolthanks. I think I've done it, though rather crudely I got something like this. Year Jan 1880-1890 -0.136363636 1891-1901 -0.406363636 1902-1912 -0.354545455 1913-1923 -0.153636364 1924-1934 -0.026363636 1935-1945 0.035454545 1946-1956 0.000909091 1957-1967 0.019090909 1968-1978 -0.04 1979-1989 0.306363636 1990-2000 0.4 2001-2009 0.691111111 I understand the need to use temperature anomalies rather absolute temperatures but I am interested in specifically how they work them out. Rather than waste alot of time telling me, if you know of a paper or two that would be handy. (perhaps you know Ricardo?) This page has some info but it is a bit basic but their description reminds me of Excel Solver. http://data.giss.nasa.gov/gistemp/abs_temp.html
  33. 1998 DIY Statistics
    #17 yocta I used excel because it's simple! Your GISS data set is commonly used and the experts say it's fine, so feel reasonably confident using it. :) If you're particularly interested, it's worthwhile taking a look at the satellite data as well (UAH & RSS are the names of the sets). You get some interesting squiggles from them; they seem more sensitive to El Nino for example, and it takes a bit more work to get an idea of what might be going on!
  34. It's cooling
    IPCC projections disproved. As a result, CO2 has nothing to do with global warming.
  35. High CO2 in the past, Part 2
    http://en.wikipedia.org/wiki/Ordovician#End_of_the_period More detail. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488.3±1.7 to 443.7±1.5 million. It ended with the Ordovician–Silurian extinction event, about 443.7 ± 1.5 Ma (ICS, 2004) that wiped out 60% of marine genera." Also of note and very relevant is the fact that dry land during the end of this period consisted of one great continent known as Gondwana. And, of most importance, these land masses were sitting over the during the time of this glacial period. Just imagine what impact on climate earth we would see if Antarctica with a current mean temperature of -57degC, was 10 times its current size. I think this glacial period was started, mostly as a byproduct of the location of Gondawana! The amount of snow which would have resulted from a land mass the size of Gondwana being located at the South Pole, both in the sea and on land, would have had a truly enormous impact on the amount of solar radiation which was being reflected back into space! In addition, sea water acts as an enormous heat reservoir. During this period of extreme glaciation, as much as 1/3 of the ocean could have been removed and deposited atop of Gondwana. The result would be less heat in the oceanic reservoirs.
  36. High CO2 in the past, Part 2
    >>>> Late in the Ordovician period, the Earth experienced glacial conditions at a time of high CO2 levels. Observe the thin grey line around 443 to 445 million years ago. How could glacial conditions occur with such high CO2 values?<<<< Answer is really quite simple. During that period of time, the earth was almost entirely covered with ice. This extremely high albedo of white ice reflected nearly all Short Wave solar energy back into space. Since no (very, very little) SW energy was being absorbed, there was virtually NO long wave IR energy being radiated from the eath. Also realize that CO2 can only absorb energy from an (8% to 20%)portion of the IR (long wave) energy spectrum. If there is no (little) LW IR energy being radiated into the atmosphere, atmospheric CO2 would have very little impact on global warming. Also think about the reality that the extremely cold air ducring this period would have also been extremely dry air. Therefore, the normal greenhouse gas impact from H2O would have been close to Zero during this period of extensive glaciation. Geological evidence indicates that what shocked the earth out of this "snowball" state was almost certainly a period of hyperactive volcanic activity. The volcanic activity served to darken the earth's surface which reduced the albedo affect and allowed the sun to warm the earth a bit. This hyperactive volcanism also put a lot of subterranian heat into the atmosphere and oceans, along with vast quantities of ash and CO2 and other gases. As the albedo effect of snowball earth was diminished over 10s of million years, the atmosphere slowly began to heat up because CO2 was there to trap some of the newly available IR energy. Also, as the earth reheated, the amount of H20 om the atmosphere increased which served to accelerate the warming process. In this instance, we can say "thank you Co2, for being there when we needed you the most!" End
  37. 1998 DIY Statistics
    RE:# 11SLRTX That looks like an excellent book, i'm requesting my library for it now... A general question about the data sets for Mark or anyone...I'm assuming the GISS data set I've linked below is one that I can use. Also is Excel a good enough program to do the analysis? http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt
  38. 1998 DIY Statistics
    NEILPERTH: You said, "I have been told that the earth is suffering from 'unprecedented global warming' as a result of man-made CO2 emmissions since about 1970." No one has ever said that. What is unprecedented in at least 10,000 years is radiative forcing, NOT temperature. There are a few other things that are unprecedented, such as temperature in at least 400 years, glacier melting in some areas, etc. See for yourself. Do a search for "unprecedented" in the AR4: http://ipcc-wg1.ucar.edu/wg1/wg1-report.html
  39. 1998 DIY Statistics
    Ned, starting from the raw data, the more you smooth the lower the chance that you get spurious short time trends. This is the zeroth order treatment of the time series, i.e. no other statistical test on uncertaintiy or significance. On the contrary, if you can manage some stitistics, you'll probably want to use the raw data. But even in this case, sooner or later you'll end up smoothing and looking at residuals.
  40. 1998 DIY Statistics
    I think woodfortrees.org is a good source to mention in this connection. It is both a DIY (though only basically univariate) analysis/checking/plotting site and data source, for example... I'm a lot more pessimistic than you about basic statistical skills and global-warming-is-over fallacies, Mark. Remember the saying: "Statistics is often used the same way a drunken man uses a light-pole: For support rather than illumination." Sadly, we can't presuppose sound reasoning, and we must be prepared to document all sorts of things that should be rather obvious by now. Tamino has just done the modeling exercise "the statistical way", without sun, but with volcanic activity and the multivariate ENSO index: http://tamino.wordpress.com/2009/12/31/exogenous-factors/#more-2150
  41. 1998 DIY Statistics
    Ned: the target I had in mind for this method was someone who has barely been introduced to statistics, so probably wouldn't think of things like uncertainty. I can't see how someone conversant in beginner stats could fall into the 'it's been cooling since 1998' -> 'global warming is over' trap anyway! Of course, there are thousands of people much better at stats than I am and maybe they'll show up my naivety...
  42. 1998 DIY Statistics
    This is nice, but it leaves open the question of the significance of the trend. By using a running mean to smooth the data, the autocorrelation will be increased dramatically. My concern with this kind of DIY thing is that someone will repeat what you've done here but then make the leap to naively interpreting the variance around the trend estimate as an actual confidence interval, which would be a big mistake. There's actually much more uncertainty in the estimate of the trend than one would think based on the smoothed data. I like Tamino's approach of looking at the temperature data many different ways -- using annual data and correcting for autocorrelation, and then just taking straightforward decadal means (NOT running means, literally plot the average from the 1970s, the 1980s, the 1990s, and the 2000s). The latter isn't as exciting, because you can't update it very often, but it does a nice job of eliminating all the autocorrelation issues. Anyway, this is all just nitpicking. Thanks for the interesting and informative post.
  43. Skeptical Science housekeeping: Translations and Comments Feed
    I must confess that Google Translator is pretty good into Spanish, but, still, you will miss some details and find some incomprehensible sentences.
  44. 1998 DIY Statistics
    Mark, Excellent post. "I tried the same trick with a quadratic equation and yet again, the averaging trick works" Be careful using the word "trick." ;-) Deniers like to use their own "tricks" to manipulate the charts to their own meaning. Unfortunately, most people don't understand how to read these charts, so they only see what they want to see. As I tell them, if you look hard enough, you can find an image of Jesus in a piece of toast. It's not enough to say there's a trend. Any trend must be supported by real-world evidence in order to properly interpret that trend. A minor point the deniers conveniently miss. To them, a trend is just a trend. One of my favorite books is "How to Lie With Statistics" by Darrell Huff. I like how Huff lines up these fallacies and explains how to filter them out. http://en.wikipedia.org/wiki/How_to_Lie_with_Statistics http://en.wikipedia.org/wiki/Misuse_of_statistics Keep up the good work! I'll keep sending folks your way!
  45. 1998 DIY Statistics
    #3: I made up the values using 0.2cos(At)cos(Bt). A and B were calculated to give periods of 4 and 8 years, and I chose an amplitude of 0.2 because peak to peak swings of 0.4C seem to have been observed before. Eg 1996-98 was a 0.4C swing in HadCRUT3 and I think it's reasonable to assume most of that was ENSO related.
  46. 1998 DIY Statistics
    neilperth, there are some problems with your procedure. You cannot use unadjusted data, if by unadjusted you mean the raw data. There are several reasons and tons of papers on the need to adjust the raw readings. You can use a single station to look for the trend; although the statitstical significance of the results will probably be rather poor. Neverthless you can try. Or, you might want to look at global averages. In this case you can not simply pick up a random and rather limited selection of stations. You need to homogenize the time series first and check for the geographical distribution, the random selection criterion do not apply in this case. A final statistical test must be applied for the significance of the result. In other words, you must make a choice local vs global (or regional), then use the right data and the appropriate procedure.
  47. What ended the Little Ice Age?
    batsvensson, what you call bandwidth (i'd call it variability) is not known a priori but can be extracted from the measurements. The signal, again, is not know a priori but can be extracted from the measurements. In practice, take the temperature data, smooth with the algorithm of your choice, take the residuals. The standard deviation of the residual is the bandwidth, the smoothed line is the signal.
  48. Climate's changed before
    As a total layman I can follow the arguments in my simple way to the point where I see that GHGs amplify warming and cooling periods, so more co2 in the atmosphere increases amplification. But when I look to see what the science says about what initiated pre-industrial inter-glacial warm and cool periods i get a bit stuck in debates about solar activity, a plethora of weather oscillations between negative and positive and now feeback loops and planet earth knowing and adjusting its own temperature because it is conscious of an energy imbalance. Global warming doesn't get any easier to understand.
    Response: Hang tight, I'm at this moment working on a post on the whole ice age/interglacial mechanism, the emphasis on making it easy to understand. Hopefully online within a day or two.
  49. 1998 DIY Statistics
    #6 & #7, global warming seems to be most easily evidenced by nighttime temperatures The above post is about trends in averages; the post I linked is about trends in record temperatures. They're really quite different things.
  50. What ended the Little Ice Age?
    RSVP and SNRatio, My comment is not considered about how well models are at making a curve fit with actual measurement or why the measured curve has the shape it has. What I am asking about is how well our understanding is of the behavior of the actual measured signal. There is no rocket science involved in this really and no reference need to be done to reality for this, but just a couple of standard test. Bern , Why do you think it is meaningful to compare variations in global mean with variations in temperatures for local weather?

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