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Tom Curtis at 09:21 AM on 5 April 2015Climate sensitivity is unlikely to be less than 2C, say scientists
PluviAL @3, I do not see any consistent evidence that the IPCC has a systematic bias to be conservative. Obviously there are instances in which they have underestimated responses to climate change, of which the most famous is Arctic sea ice extent, but there are also other areas in which they have overestimated the response. One of these is Global Mean Surface Temperature, where their predictions have been consistently warm relative to observations (if only by about 15%). The pattern of some areas underestimated and some overestimated is what we would expect with imperfect knowledge and no institutional bias. Of course, it is possible that if all areas are taken into account, a bias exists; but no meta-study comparing IPCC projections with observations across all areas of climate science exists (if we exclude the IPCC reports themselves). What is more, such independent reviews of the science as exist, while less comprehensive than the IPCC, tend to agree with the IPCC in the areas of overlap.
More importantly, climate scientists have been surveyed about the accuracy of the IPCC reports, and while some think it conservative, others think it to adventurous, but the majority think it reasonably accurate. As the IPCC is supposed to report on the scientific consensus, that suggest they are doing their job well.
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PluviAL at 04:22 AM on 5 April 2015Climate sensitivity is unlikely to be less than 2C, say scientists
My simple reading of the process, is that the IPCC has a systematic bias to be conservative. What this mean is that we are more likely to continuously find that they produce underestimates.
By my same simple outlook, we must develop tools to address, and use all feedback mechanisms; not just such clumsy ideas as ocean clouding with salt spray, or high atmosphere areoles. We can develop powerful tools that use the energy in the atmosphere itself to produce feedback mechanisms at the desirable levels to attain the adjustment we must have, and to change it when a different outcome is desired as we find that we made a mistake or, we need one effect in one region but the opposite in another.
For example: If the gulf stream slows or stops, we may have to warm Europe, and cool Australia at the same time. Such tools must be developed and advanced. We can do it; don’t just say it is impossible without knowing the relevant arguments.
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Elmwood at 02:46 AM on 5 April 2015Climate sensitivity is unlikely to be less than 2C, say scientists
I thought ECS as found in the geologic record averages around 3 degrees celcius? Models should not be used as the only line of evidence for estimating what ECS will be.
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denisaf at 22:48 PM on 4 April 2015We must defend science if we want a prosperous future
The article deals with why society should take more notice of scientific findings. i am a retired aeronautical research scientist so have an interest in this issue. It is often said that science if advancing the frontiers of knowledge. The reality is that advances in physical science are illustrating how much knowledge of physical operations were unknown, so by extrapolation, how much is still unknown. Science has only fairly recently provided understanding of the deleterious aspects of the combustion of fossil fuels to supply energy. That has been a major failing of science but there are many others.
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ranyl at 22:01 PM on 4 April 2015Sea Level Rise is Spiking Sharply
Thanks Tom,
I never thought iceshelf per se collapse would cause a sea level rise for sure, th ebreak up of the above sea level icesheet itself.
The natrue image is quite schematic also mind :), and the line number 3 in the Antartica Glaciers image does seem to show quite a hollow developing, as for Icesheet section break up due to undermining, it is all going to depend on the rate of underwater melt, the slope of dropoff and the rate thinning on top.
Overall however do still the potential for sudden icesheet edge instability due to undermining. Looking at the topography here past the GL point is melting at bottom, still do wonder about an undermined column scenario?
And looking at Thwaites, past that 150km ridge and it looks like a steep column again, with a very thick above sea level icesheet.
Anyway can't help suspecting that the melting of these seabed grounded icesheets is going to be interesting to watch, full of little surprises and is an accelerating situation as things aren't going to cool down anytime soon.
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bozzza at 18:35 PM on 4 April 2015We must defend science if we want a prosperous future
How can all Labor voters be called intellectual?
Moderator Response:[GT]
Bozza
If you have something of substance to say wrt this piece fine, but one-liner drive-by's don't cut it and breach site guidelines.
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bozzza at 18:30 PM on 4 April 2015Understanding adjustments to temperature data
..more like a "repetition versus error-of-repetition"(my summation atleast) concept according to him... but I only read 3/4 of it I must admit before I lost the thread so,..!!
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bozzza at 18:25 PM on 4 April 2015Understanding adjustments to temperature data
@ 57, I read The Mechanism of Mind by Edward Debono once and he was saying that the error of the mind was what made it work so efficiently and/or effectively plus or minus a few definitions of accuracy(lol)... so kind of the same thing!! (...it was a repetition versus error type scenario like what you are saying, perhaps!)
- perhaps not, but I'm willing to bet the book has bred ideas!
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Glenn Tamblyn at 17:30 PM on 4 April 2015Sea Level Rise is Spiking Sharply
Pluvial.
There is another aspect to consider. We have also increased our above ground water storage, our empoundment. I don't have the figures to hand (maybe someone else can find them) but I seem to recall that a study found that the depletion of groundwater is , seredipitously, roughly balanced by the increase in above ground water storage in dams etc.
Another factor to consider. Although we aren't in much of an El Nino at present we have had 'the El Nino you are having when you aren't having an El Nino' for some time now. This might be a factor.
Look at Figure 1 in the post, around 1997/98 when the big El Nino happened. Sea level spiked up for the opposite reason to the drop in 2011. Maybe an El Nino-lite is contributing to current SLR.
Also, we have had high sea surface temperatures in the north Pacific recently. If this reflects recent heating of the upper levels of the ocean there this might be a factor. The Coefficient of Thermal Expansion for water varies significantly with temperature. Warming already warm water produces greater expansion (which we would see as SLR) than warming cold water by the same amount.
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PluviAL at 14:54 PM on 4 April 2015Sea Level Rise is Spiking Sharply
Underground water is roughly equal to the water content in the cryosphere. If we have drawn 65 km3 from 2004 to 2013, then India, China, Arabia, Brazil, Argentina, Australia, and central Asia, probably have overdrawn a ground water by similar figures. At 65 km3 by each area, that only accounts for 1 mm of SLR.
Somehow it seems that this figure is under-considered, and thus under-estimated. If the potential contribution from ground water is equal to the cryosphere, and we have been sucking on that tit as hard as on the fossil fuels, then it might be that there is a lot more SLR that has to be accounted for. Thus, this “spike” might not be an anomaly, but what it looks like; a real rise in sea level.
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chriskoz at 13:24 PM on 4 April 2015We must defend science if we want a prosperous future
I have hard time understanding the authors association of "deconstructionist mind-set" with "intellectual Left". The definition of "deconstructionism" apears in here:
But from the Left, or some segments of the intellectual Left, a deconstructionist mind-set has partly undermined an evidence-based approach to policy making or problem solving
and here:
The pluralist or deconstructionist or post-modern theory of knowledge is contemptuous of expertise, rejects the idea of hierarchies of knowledge and asserts the democratic mantra that –- as with votes in elections –- every opinion is of equal value, so that if you insist that the earth is flat, refuse vaccination for children or deny that HIV-AIDS is transmitted by virus, your view should be treated with respect.
That has nothing to do with "intellectual Left" which, at least in Australia, means support of pro-labour, pro-social, and pro-environmental policies.
The deconstructionism, as described above, can be attributed equally to both Left and Right. E.g. current PM, Tony Abbott, a hard-core right winger, can easily be described as a "deconstructionist" literally as described above. As an opposition leader, he used to critique all policies of the governing Labor party very successfully. In fact he built his entire political career on the deconstruction of his political opponents.
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chriskoz at 12:45 PM on 4 April 2015We must defend science if we want a prosperous future
Tom@3,
The tragedy is that straightforward evidence based reasoning strongly supports a left wing point of view.
Can you elabrate that point? I have not heard such opinion yet. Do you mean, that right wingers are unable/less able to accept evidence than left wingers? Do you mean such observation aplies to Australian/Westminster political system, or any contemporary system in general?
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Tom Curtis at 12:33 PM on 4 April 2015Sea Level Rise is Spiking Sharply
ranyl @25, that image is very schematic. A more detailed image is avialable from Nature:
As you can see from the third panel, by "thinning" they mean the reduction of the domed section. That is a direct consequence of the faster flow, which in turn is a consequence of the reduction in the extent of the floating ice shelf along with the retreating grounding line. Because the Pine Island Glacier is in fact a glacier, it will be transversed by a large number of crevases meaning structural support of the ice beyond the grounding line will be virtually non existent, ie, virtually all ice beyond the grounding line will be floating ice.
As to sudden increases, it was calculated by Noerdlinger and Brower that "If all the extant sea ice and floating shelf ice melted, the global sea level would rise about 4 cm." Clearly not all of the floating ice will melt in a year, or even 50 years. Ergo "sudden increases" from the collapse of ice shelves are unlikely to contribute more than a millimetre or two to sea level rise in any given year, and probably not even that. For comparison, Shepherd et al calculate a 0.49 mm contribution to sea level rise from the melting of floating ice from 1994-2004. That comes from a reduction "...that exceeds considerably the reduction in grounded ice over the same period", something we would expect to continue.
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ranyl at 11:36 AM on 4 April 2015Sea Level Rise is Spiking Sharply
Sorry if the image is too big,
http://cdn.antarcticglaciers.org/wp-content/uploads/2013/07/PIG.ai_.jpg
Thanks Tom,
I agree the ice shelf is definately floating and supporting the icesheet edges.
Looking at the line 3 on this graphic, (present day), it seems that the domed bit above the water line is not floating and is still suported by the ice pillar below, which is looking more and more eaten into.
If the weight of that domed above sea level supported part of the icesheet became such that the water in the cavern and the ice column couldn't support it anymore (the pillar is shrinking and I think the icesheet is gaining weight due to regional warming induced more snow). I know it is only a graphic but on this one more but on yours as well I can imagine a reasonable sized section of above sea level icesheet sort breaking off, and I think those icesheets hold quite alot of ice, up to a 1m Pine Island I think, so I do wonder if a couple of cm's of sealevel rise worth could snap fall off from time to time as the below sealevel WAIS icesheet melts away?
Not sure about the whole topography however thankfully looking at your graphic (23), the undermining may only come from one side, unless that is just a matter of section?
Not sure about the topography of the EAIS marine based glaceirs that are melting and the icesheets there, but they are being under eroded below the sea as well. And I think these basins and similair basins in Greenland are quite big, and are several kilometers deep, so the Ice replacement effect might be putting a very small brake on apparent sea level rise, but might be masking some melt.
I've not read an estimation of the amount or volume of underwater ice being melted on the marine based icesheets and glaciers, just overall icesheet and glacial loses and therefore I don't have any feel for the sieze of the effect, but it will increase as the melting accelerates?
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Leto at 09:39 AM on 4 April 2015Understanding adjustments to temperature data
Bob @ 58,
Very good points. The common practice of reporting a single error range for an instrument doesn't help general understanding. It would be nice if it were standard practice to separate out components that are random from reading to reading (and hence average out) versus components that are systematic/consistent (and hence irrelevant to measuring changes). There is a spectrum between these types of errors (and other subtleties as explained in your post), but some convenient way of reporting both error dimensions would be nice.
My quick Java example is of course based on an unrealistic error distribution introduced artificially by rounding. In that example, an increase of 0.002 is manifested as a one fiftieth chance of a 0.1 upwards step occurring. In a real instrument, there would be a more complex error distribution.
As someone else said up above, this could be a topic for another SkS post. There does seem to be significant confusion on the issue in denierville.
Tom Curtis @ 57,
Nice pics. The example best known to me is picking up the tiny elecrical signal coming from the first phase of visual processing, and hence measuring the speed of transmission in the optic nerve non-invasively, merely by averaging out the time-locked EEG signal over the back of the head while a subject looks at a flashing checkerboard pattern. Everything evenually averages out to nothing apart from the activity that is locked to the flashing.
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Kevin C at 09:12 AM on 4 April 2015We must defend science if we want a prosperous future
I'm also unhappy with the significance attached to deconstruction in this article. The same attitudes to knowledge are also symptomatic of a post-modern world view, and I am not convinced that the post-modern worldview has been signficantly influenced by deconstructionism - I think there are probably plenty of other drivers which may have caused it's emergence.
It is entirely possible that deconstruction itself was a response to the same drivers which led to the emergence of a post-modern worldview in non-academic circles.
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Bob Loblaw at 08:21 AM on 4 April 2015Understanding adjustments to temperature data
Although I am not in disagreement with what has been disucssed in the last few days, there is another characteristic of temperature sensors that has been missed. Although the previously-mentioned accuracy of +/-0.1C is fairly typical of meteorological sensors, that accuracy specification does not quite mean what some seem to be assuming it means.
For example, Vaisala is a manufacturer of very commonly-used meteorological sensors, and they make a combined humidity/temperature probe (HMP155) that is in widespread use. It specifies a +/-0.1C accuracy. That value, however, is not a random error for a single reading from the instrument - it is the random error for a large number of instruments over the temperature range in question. What that means is if that you buy 100 HMP155s, they will all tell you the same temperature to within +/-0.1.
For a single sensor/instrument, however, the error is not particularly random. A specific sensor will typically be a bit high or a bit low, and will remain at a pretty constant offset from the real temperature. So, when looking at a change in temperature, you can accurately detect a very small change, even though you're not quite sure of the exact temperature itself.
Mathematically, the error in the temperature change is related to the error in each reading as follows:
deltaT + errordeltaT = (T2 + error2) - (T1 + error1)
which makes
errordeltaT = error2 -error1
If error2 and error1 are the same, there is no error in the difference. Note that the above equation applies to one specific pair of readings, not the distribution of errors for a large number of readings.
The key factor, when considering the distribution of errors (i.e., what errors are expected from a large number of pairs of readings) is the covariance between errors. If the covariance is zero (the two errors are completely independent) then we have random errors, and the whole averaging process described above will apply. When the two errors vary in lock-step, the sensor can have very poor absolute accuracy and still detect small changes accurately from a single pair of readings. WIkipedia's Propagation of Uncertainty page does a reasonable job of discussing some general principles.
Given that any normal weather station and network of stations will keep a single instrument installed at a single station for a long time, it is the error relationship for that individual that is important. Even at a single station, over a short period of time, temperature changes can be measured accurately.
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Tom Curtis at 07:04 AM on 4 April 2015Sea Level Rise is Spiking Sharply
anthropocene @22, the impression of increased amplitude of fluctuation arises almost entirely from the reduction in sea level associated with the 2011/12 La Nina. By one measure, that is the strongest La Nina event in on record (for a record going back 130 years). It is also a single event. I would wait a few years to see whether or not it is an aberration or signals the start of greater osscillations before drawing any conclusions about the damping.
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Tom Curtis at 06:59 AM on 4 April 2015Sea Level Rise is Spiking Sharply
ranyl @19, sorry for the delayed response.
I now get were you are coming from, and yes, the undercutting of grounded ice shelves by warm water at the base of the ice shelf will initially reduce the volume of water and hence promote a fall in sea level. That is due not only to the relative densities, but because the excess water above the undercut remains supported structurally by the grounding of the ice. When the undercut is sufficient, however, that structuraly integrity will be lost, with the result of an overall increase in sea level.
Having accepted that, however, I will point out that most ice shelves are actually floating (as with the Ross Ice Shelf as illustrated below), so that this mechanism does not apply. melt of the underside of a floating ice shelf will result in the ice riding lower on the water, with an overall slight rise in sea level. Because of that, and because the collapse of the ice shelf will progress more or less continuously with melt back even of grounded ice sheets, I do not think the mechanism you indicate will be important, and will always be outweighed by other effects.
You are correct that the reduced volume of the water once melted at the grounding line will draw in more warm water. Further, the newly melted water will be bouyant because less dense then the salt water. Consequently it will rise away from the melt point, thus drawing in more warm water. I suspect that this, by volume, is the larger effect, and is certainly the mechanism discussed in popular explanations by the experts, however, the mechanism you describe will also operate.
Finally, I do not think this will result in sudden jumps in sea level rise, primarilly because the total effect is so small.
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Tom Curtis at 06:33 AM on 4 April 2015We must defend science if we want a prosperous future
ralbin @1, in Australia at least, deconstructionism is a pervasive feature of the academic left, and consequently highly influential on policy development if not on the thought processes of ordinary Australians. Further, the teaching of deconstructionist perspectives has penetrated deep into the pre-university curiculum. The result is pernicious in both cases. I strongly suspect the same is true in parts of Europe, particularly France. The tragedy is that straightforward evidence based reasoning strongly supports a left wing point of view. The influence of deconstructionism weakens the left wing of politics.
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DSL at 02:31 AM on 4 April 2015We must defend science if we want a prosperous future
Say rather "deconstructionism" is a largely inconsequential technique or strategy. Unless, of course, it appears as a feature of postmodernity. Postmodernity isn't a choice, though. It's what happens when, to quote Jameson, people "attempt to think the present historically in an age that has forgotten how to think historically in the first place." History becomes a sort of commodity or means to produce exchange value or to protect the flow of capital. History is altered, taken apart, reconstructed to fit and encourage the dominant narrative of the production of capital. The more we help people understand their conditions, and help them understand their own roles in developing the historical narrative that contains but is not manipulated by the narrative of capital, the more we help create a culture capable of collectively grasping the reins of the long-term future of the species.
It seems unlikely that we'll be able to do that. Nature, that overarching narrative we think we've moved beyond, will likely lend a violent hand in encouraging the critical thinking skills of the general public, unless such violence ends up associated with various deities. We're not good at taking responsibility right now.
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ralbin at 01:51 AM on 4 April 2015We must defend science if we want a prosperous future
A bit of false balance here. Deconstructionism is a largely inconsequential movement, though it may be different in Australia, with very little impact on this particular debate. Any problems produced by the "intellectual Left" pale by comparison with the shameless activities of conservative politicians and their enablers.
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BojanD at 21:42 PM on 3 April 2015Ipso proves impotent at curbing the Mail's climate misinformation
ryland, I suppose they could do that. But just because they could do something else doesn't make the alternative they chose deceptive. It's not even remotely similar to what Rose did, which was deliberately deceptive.
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Tom Curtis at 20:42 PM on 3 April 2015Understanding adjustments to temperature data
Leto @56, the most stunning use of these principles I know of actually comes from amateur astronomy. In a new technique, amateur astronomers take thousands of images of the object they are interested in. They then use computer programs to "average" the images. The result is an image far sharper than any of the individual images used, and indeed sharper than they could achieve with the same exposure time using conventional techniques. For example, these three images were taken on a 16 inch newtonian telescope:
And this is one of the individual images from the "stack" used to create the Jupiter image above:
The truly amazing thing here is that not only does averaging bring out a far higher resolution image, but without the introduction of noise by the atmosphere, all the images in the stack would be identical, and no image improvement would be possible. So, in this case not only does averaging eliminate noise, and allow a far higher resolution than is possible by the original instruments, but the noise is in fact necessary for the process.
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Leto at 19:08 PM on 3 April 2015Understanding adjustments to temperature data
Quick,
As a demonstration of what Tom Curtis and Tom Dayton have been sayng, I wrote a quick Java program. It produces 5000 random values between 0 and 20, computes the average and then "warms" them by adding 0.002 to each value and recomputing the average. Not surprisingly, the new average is close to 0.002 above the old one (some errors creep in because of Java inaccuracies - these could be fixed with a more sophisticated approach.)
When the initial and adjusted values are accessed through surrogate values that have been rounded to the nearest 0.1, the difference between the averages is still very close to 0.002 - even though most of the rounded values are the same before and after the warming, just enough are increased that, on average, the 0.002 warming can be recovered.
Typical output:
Test of ability to measure difference of 0.002 with 5000 instruments rounded to nearest 0.1
Start with 5000 random values in range 0 to 20
Sample:
Baseline Warmed
17.555315017700195 17.557315017700194
6.136661529541016 6.138661529541015
12.851906776428223 12.853906776428223
18.39383888244629 18.395838882446288
3.099104166030884 3.1011041660308836
5.749928951263428 5.7519289512634275
18.21527862548828 18.21727862548828
2.304227352142334 2.3062273521423338
5.495196342468262 5.4971963424682615
7.890586853027344 7.8925868530273435
Average of initial values 10.034636362266541
... add 0.002 to each value
Average of new values 10.036636362266911
True difference 0.00200000000037015Now round initial and final data sets to nearest 0.1...
Sample:
Baseline Warmed
17.6 17.6
6.1 6.1
12.9 12.9
18.4 18.4
3.1 3.1
5.7 5.8 *
18.2 18.2
2.3 2.3
5.5 5.5
7.9 7.9
Average of rounded values 10.034260000000016
Average of rounded new values 10.036380000000015
Measured difference derived solely from rounded values 0.0021199999999996777
Output is different every time, but the general principle holds.Code below:
/////////////////////////////////////////////////
import java.util.Random;
public class Average {
static double[] values ;
static double[] newValues ;
private static final int NUMVALUES = 5000 ;
static Random random = new Random();
public static void main(String[] args){
System.out.println("Test of ability to measure difference of 0.002 with " + NUMVALUES + " instruments rounded to nearest 0.1\n") ;
System.out.println("Start with 5000 random values in range 0 to 20" );
values = new double[NUMVALUES] ;
newValues = new double[NUMVALUES] ;
for(int n=0; n<NUMVALUES; n++){
values[n] = random.nextFloat()*20;
newValues[n]=values[n]+ 0.002d ;
}
double average = Average(values) ;
double newAverage = Average(newValues) ;
double[] roundedValues = Rounded(values) ;
double[] roundedNewValues = Rounded(newValues) ;
double measuredAverage = Average(roundedValues) ;
double newMeasuredAverage = Average(roundedNewValues) ;
System.out.println(" Sample:\nBaseline\t\tWarmed" );for(int n=0; n<10; n++) {
System.out.println(" " + values[n] + "\t " + newValues[n] );
}
System.out.println(" Average of initial values " + average);
System.out.println(" ... add 0.002 to each value ");
System.out.println(" Average of new values " + newAverage);
System.out.println(" True difference " + (newAverage-average)) ;
System.out.println();
System.out.println("Now round initial and final data sets to nearest 0.1..." );
System.out.println(" Sample:\nBaseline\tWarmed" );
for(int n=0; n<10; n++) {
System.out.print(" " + roundedValues[n] + "\t\t" + roundedNewValues[n] );
if(roundedValues[n]!=roundedNewValues[n])
System.out.print(" *");
System.out.println();
}
System.out.println(" Average of rounded values " + measuredAverage);
System.out.println(" Average of rounded new values " + newMeasuredAverage);
System.out.println(" Measured difference derived solely from rounded values " + (newMeasuredAverage-measuredAverage)) ;
}private static double Average(double[] vals){
int len = vals.length ;
double sum = 0 ;
for(int n=0; n<len; n++){
sum+=vals[n];
}
return sum/len ;
}
private static double[] Rounded(double[] vals){
int len = vals.length ;
double[] rounded = new double[len] ;
for(int n=0; n<len; n++){
rounded[n] = (int)(vals[n]*10 + 0.5f);
rounded[n]/=10f ;
}
return rounded ;
}
}/////////////////////////////////////////////////
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Tom Curtis at 18:45 PM on 3 April 2015Understanding adjustments to temperature data
scaddenp @54, the ERSST v3 introduced the use of satellite data, but in v3b, they ceased using satellite data as it introduced an identified spurious cold trend due to difficulties in determining clear sky conditions. I do not have access to the full paper of Huang et al (2014) so I don't know if v4 reintroduced satellite data again. I note, however, that satellites are mentioned only twice in the abstract, once with reference to an institutional affiliation, and once with reference to a cross product comparison. That suggests that they have not.
As a side note, Liu et al (2014) is the estimate of uncertainty for ERSST v4 - further ammunition for Quick if he still needs it ;)
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scaddenp at 17:59 PM on 3 April 2015Understanding adjustments to temperature data
Tom, my reading of the metadata for ersst is that they use satellite data from 1985, since v3 as well as icoads and Huang v4 change method but not input.
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Tom Curtis at 09:42 AM on 3 April 2015Understanding adjustments to temperature data
Glenn Tamblyn @52, until recently GISS used surface observation based data for SST except for the last few years in which they used satellite based data. They now use NOAA ERSST which in turn is based on ICOADS, a dataset of surface based observations. The HadCRUT4 index uses the HadSST3 dataset for SST, which is in turn also based on ICOADS. The NCDC (NOAA) uses the ERSST. BEST (Berkeley) uses HadSST3. UAH and RSS use satellite observations exclusively, but observer the atmosphere rather than the surface, and hence do not have observations of SST directly. Consequently I am unaware of any commonly used temperature series that currently uses satellite observations of SST.
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Glenn Tamblyn at 09:08 AM on 3 April 2015Understanding adjustments to temperature data
Quick
And another point to remember for future reference. 70% of the world is oceans and the major temperature series are land and ocean combined data. Land surface air temperatures and ocean sea surface temperatures. Much of the recent peak was due to warmer SST's, particulaly in the north pacific.
And SST's are measured by satellites, not RTD's.
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anthropocene at 08:58 AM on 3 April 2015Sea Level Rise is Spiking Sharply
It seems that the comments and the original article are missing the most striking aspect of the graph. The graph looks like a heavily damped system with a relatively weak forcing acting on it. However in the last few years the impact of the forcing has had a much bigger effect causing bigger fluctuations in the SLR. Classically this could be because of two things: the damping has decreased or the forcing has increased. Since I assume the damping comes mainly from the sheer size of the oceans which hasn't changed the change in behaviour must be caused by an increase in the forcing. The article implies that El Nino/La Nina has a large role to play but the current fluctuation is much bigger than that of the 'super' El Nino of 1998. So is what is currently going on bigger than 1998 or is another factor adding to the forcing? e.g. El Nino conditions cause more ice melt?
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John Hartz at 07:52 AM on 3 April 2015Global warming and drought are turning the Golden State brown
Recommended supplemental reading:
California Tuolumne snowpack 40 percent of worst year by By Alan Buis,
Jet Propulsion Laboratory, NASA Global Climate Change News, Apr 2, 2015 -
Quick at 06:10 AM on 3 April 2015Understanding adjustments to temperature data
Tom Dayton. Great explanation! Thanks again. "Stefan_Z" has gone off the grid since I slapped him with some of this info that you and Tom C. provided.
My mission continues: "Saving the world from willfull ignorance, even if it's only one denier at a time."
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Tom Dayton at 03:36 AM on 3 April 2015Understanding adjustments to temperature data
Quick, a simple(istic) explanation of the Law of Large Numbers applied to this case is that each temperature measurement is a sample from the infinitely-sized population of all possible measurements of the "true" temperature value. Each measurement probably is erroneous in that probably it differs from the true temperature. But each measurement is randomly erroneous in direction and size from the true temperature, so a collection of those sample measurements will have some measurements' errors cancel out other measurements' errors. The probability of that collection of measurements completely cancelling its errors--and so revealing the true temperature--increases as the size of that collection grows. Therefore growing the size of the collection narrows the range of temperatures in which we can be "confident" the true temperature lies--no matter what probability/certainty you prefer as your definition of "confident." To use an example with less emotional baggage than global temperature, consider flipping a coin to find its true probability of coming up heads. The more trials you run (i.e., the more flips, the more measurements), the more likely that the averages of the numbers of flip results (heads vs. tails) are the "true" values.
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Quick at 03:06 AM on 3 April 2015Understanding adjustments to temperature data
Thanks again, Tom Curtis (and Tom Dayton)! I spent a copious amount of time trying to get info like this by simply Googling, but wasn't getting much...
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ubrew12 at 02:58 AM on 3 April 2015Climate sensitivity is unlikely to be less than 2C, say scientists
"Other scientists argue "transient climate sensitivity" is a more policy-relevant measure" because the policy of ignoring the effects of AGW, like the now-melting permafrost, has worked 'so well' in the past.
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Tom Dayton at 01:45 AM on 3 April 2015Understanding adjustments to temperature data
Quick, for more on Tom Curtis's explanation, look up the Law of Large Numbers.
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Tom Curtis at 01:33 AM on 3 April 2015Understanding adjustments to temperature data
Quick @46, GISS (NASA) do not collect any thermometer records themselves. Rather they use the data collected by NOAA for the Global Historical Climate Network (GHCN), plus some additional stations in Antarctica an one additional station in Germany. In the US, the GHCN stations are just the US Historical Climate Network (USHCN) stations, with the data again collected by NOAA, and I believe much of it administered by NOAA. Elsewhere in the world, the data will come from various national meteorological stations.
As to which sensors are used, a whole host of different sensors both in different countries and within countries are used. All are approximately equivalent to thermometers in a Stevenson screen, but each will have their own error in measurement. GISS (and the NCDC) take that initial error rates and calculate from it the error in their overall temperature index using techniques similar to those I illustrated. It is not a simple as my illustration because not all instruments are the same, and the calculations are not taking simple averages. However, they are taking an average of a sort so that with a large number of station records, the error becomes a small fraction of the error of individual stations for reasons exactly related to those I illustrated.
The crucial point here is that denier you quote is ignoring the most fundamental fact about error propogation with respect to averages, while boasting of his great knowledge of the topic. His argument simply does not hold water. In contrast to his bombast, however, GISS, and the NCDC, and the Hadley Center and CRU teams, and the BEST team, and the JMA have all tackled these issues, worked out the error correctly, and published their methods and results in peer reviewed literature. And all five teams get essentially the same results with only slight divergences based on the data sets and methods used.
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Quick at 00:05 AM on 3 April 2015Understanding adjustments to temperature data
Thanks Tom. Are the NASA sensors used only for US temps? If not, what other type of instrumentation is used by the GHCN and for SST measurements?
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billthefrog at 23:53 PM on 2 April 2015Sea Level Rise is Spiking Sharply
sgbotsford #10
"Education please:"
I'm afraid that I honestly don't know how to take your comment, as there are at least two diametrically opposed interpretations.
Interpretation 1) It could be taken as someone simply saying ... "I don't believe it's possible to make such measurements, and here's some throwaway remarks as a form of justification", or, in its more basic form "I don't understand that, therefore nobody can understand that, therefore it ain't true".
If that's the case, there's no point trying to respond beyond what Tom C and CBD have already said.
Interpretation 2) On the other hand, your question could be entirely genuine, and I could be utterly misreading the tone of your remarks. In which case, please ignore Interpretation (1), and read on ...
If you want to see some introductory stuff about the measurement of sea level, a very simple starter would be this article in National Geographic. In addition, there is a reasonable Wikipedia article on Sea Level which discusses some of the points you make. Both articles make reference to the 19-year Metonic cycle, by which you can easily grasp that sea level measurement takes time - lots of it!
At a somewhat more advanced level, you could try ploughing through the voluminous material produced by the Permanent Service for Mean Sea Level. The PSMSL is part of the UK's National Oceanograhy Centre in Liverpool.
The link provided takes you to their sea level training page. From there, you can access some very detailed material. For example, Vol 1 of the training manual goes to about 60 pages - before the Appendicies.
cheers bill f
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billthefrog at 22:45 PM on 2 April 2015Sea Level Rise is Spiking Sharply
ranyl #20
If you're interested in the effects of sea ice melt, there was some discussion on John Hartz's Weekly Roundup 11a. The relevant portion starts at about Comment # 11.
cheers bill f
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CBDunkerson at 22:20 PM on 2 April 2015It hasn't warmed since 1998
JohnD wrote: "Perhaps a major issue is only the poor predictions are making it to the media..."
You have yet to identify, let alone substantiate, even one of these supposed 'poor predictions'. Until you do so it is not 'pretentious and condescending' to dismiss your position... because you have not presented a position.
Try to look at it from the other side. People who do not consider themselves to be acting on "blind faith" and "religious-type fervor", but rather accepting the strong scientific consensus based on the overwhelming evidence. Then you come in proclaiming that they are all wrong, while refusing to cite any evidence for your position and ignoring evidence to the contrary provided to you. Some might call such behaviour 'pretentious and condescending'.
If they were being kind.
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CBDunkerson at 22:01 PM on 2 April 2015Scientists link Arctic warming to intense summer heatwaves in the northern hemisphere
Watchdog wrote: "IF that "red" data is true, than, yes, it's at least an eye-opener."
In addition to Tom's point about having used the most extensive data set... it really doesn't matter. BEST, UAH, RSS, HadCRUT, GISS, NCDC, et cetera... you could use any of the different surface temperature data sets and at the scale shown on that graph the differences would barely be visible. That is, they all show the recent warming spike being greater than anything in the pre-industrial proxy records.
So there really is not any question "IF" that data is true. The surface temperature datasets produced by skeptics (e.g. UAH & BEST) show results virtually identical to the various government and other independant datasets.
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Watchdog at 21:24 PM on 2 April 2015Scientists link Arctic warming to intense summer heatwaves in the northern hemisphere
RobH@42, TomC@44 - Thank you for your informative responses.
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ranyl at 20:49 PM on 2 April 2015Sea Level Rise is Spiking Sharply
"2) The melting of floating ice actually raises sea level slightly due to the different densities of saline water (as found in the sea) and fresh water (as found in ice). Grounded ice, which by definition is not floating, and hence has more volume than an equivalent area of barely floating ice must raise sea level rise even more. Ergo when grounded ice is undercut be melting, that melting provides sufficient water to fill the cavity, and then some."
Thanks Tom for the area expansion calculations, a small effect the sea is huge.
On the above I'm not sure that the melting of below sea level seabed grounded ice will raise sea levels.
1029 kg/m3 Sea Water
999 Kg/m3 Density of fresh water
916 Kg/m3 Density of Ice
For from these figures if you melt a 1m3 of ice you produce 916kg of freshwater, which occupies a volume of 0.917m3, leaving a volume of 0.083m3, or ~8% of the original volume of the seabed grounded ice has to be replaced with sea water. Therefore 8% of whatever volume that is being melted at the bottom of the seabed grounded ice sheet needs to be replaced by incoming sea water? ...?
Lastly if this 8% replacement is the case, I wonder if this dynamic volume deficit may also draw the sea water in, and as the low density fresh water also needs to be replaced as it floats away it alsodraws in bottom waters, and I wonder if this drawing in affect may accelerate the bottom melting to a degree, as the drawn in bottom waters are also warmer than the fresh water being replaced?
For the query on the possibility of more sudden jumps in sea levels and the undermining melting of seabed based icesheets, I wasn’t meaning the floating ice shelves; I was talking of icesheets themselves that are seabed grounded. I am asking basically, can undermining the supporting below sea level part of the seabed grounded icesheet possibly result in large side collapses of the above sea level part of the icesheet as its underlying support structure is melted away, raising sea levels more abruptly?
Yes William I agree the additional sea level to coast lines away from the Antarctica and Greenland icesheets melt and stop pulling water towards themselves is a worry. 1m of additional seawater volume melted from the icesheets doesn’t mean a local sea level rise will be anything like 1m and there will even be falls in sea level in areas around Greenland and Antarctica as a result.
Also over the longer term the depressions the icesheets are sitting in, are going to flatten out again as the immense weight of the icesheet are removed. This now sunken ground wasn’t below sea level when the ice started accumulating, it was that the weight of the icesheet as the ice accumulated that sank the ground it sat on and thus formed the below sea level hollow the seabed grounded icesheets currently sit in. I do wonder what the seismic consequences of a rapid melt will be; what does the rate of removal of the weight of an ice sheet have an effect on the seismic response? Quick removal sudden larger seismic events slow removal slow adjustments?
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billthefrog at 20:40 PM on 2 April 2015Matt Ridley is wrong again on fossil fuels
As I was starting to articulate some thoughts on this thread, I was overtaken by a strange sense of déjà vu.
Checking the SkS archives threw up (tee hee) many references to Ridley, in particular a piece that Dana wrote in January of this year. Any reader unfamiliar with Ridley may find it profitable to peruse that posting in conjunction with this one.
Nothing has changed in the interim that would even remotely lead me to consider revising my comment (#3) on Dana's earlier thread.
cheers Bill F
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Tristan at 19:44 PM on 2 April 2015Understanding adjustments to temperature data
FWIW I think a post specifically referencing the point Tom just made would be productive.
I've spent a lot of time in denierville and a regular assertion is 'You can't get temps/sea-level etc to 3 sig figures when instrumentation is barely accurate to the nearest degree. -
PhilippeChantreau at 16:11 PM on 2 April 2015Scientists link Arctic warming to intense summer heatwaves in the northern hemisphere
Perhaps others have not noticed watchdog, but I was amused to see how you went from an unsupported argument of Arctic climate, to side-stepping the very real and very objective notion of statistical significance to now shifting to global climate.
As for ice, it is really irrelevant how you want to measure it. You still can not pull together any evidence that the increase you trumpeted earlier exists. I see no point wasting any more time.
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One Planet Only Forever at 14:50 PM on 2 April 2015Matt Ridley is wrong again on fossil fuels
Matt Ridley can be debunked just by addressing his opening salvo.
"To throw away these immense economic, environmental and moral benefits, you would have to have a very good reason. The one most often invoked today is that we are wrecking the planet’s climate. But are we?"
There is no moral justification for a few among a generation of humanity getting way with benefiting form activities that the rest of humanity will not be able to benefit from through the hundreds of millions of years this amazing planet will be habitable. And it is immoral for anyone to try to excuse a few in this generation benefiting as much as they can get away with through the fatally flawed economic system of profitability and popularity.
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Tom Curtis at 13:48 PM on 2 April 2015Understanding adjustments to temperature data
Quick @40, suppose you have a single instrument with an accuracy of 0.1 C. Then for that station the best accuracy we can have is 0.1 C, and other factors may cause the error to be greater. However, if we want to determine the average temperature of 10 different sites, each using the same type of instrument, the error becomes the error of the average, ie, the square root of the additive sums of each error term, divided by the number of terms. For 10 sites, that turns out to be again 0.1 C. If we increase the number of sites to 100, the error margin, however, drops to 0.0316 (= ((0.1*100)^0.5)/100). With a thousand sites, it drops to 0.01. With 10 thousand sites it drops to 0.00316, and so on.
The USHCN has 1221 stations within the contiguous United States. The error on the simple average of that many stations assuming an instrumental error of 0.1 C is 0.009 C. The GHCN has around 2500 stations, yielding an accuracy for the simple average of 0.006 C. These figures are for the land only temperatures. On top of that there are thousands of SST measurements that go into the Global Mean Surface Temperature.
Clearly your denier's point is invalid. The quoted errors of the GMST are well above that which would be obtained from taking a simple mean. That extra is to account for other sources of error, the accounting of which has been detailed in peer reviewed papers.
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bozzza at 13:37 PM on 2 April 2015Sea Level Rise is Spiking Sharply
@15, this question begs an equally pointed one : "How long actually is the delay between carbon emission and sea level rise?"
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