<p>Firstly, the RSS and UAH datasets do not "line up nearly perfectly", the diagram below shows both products over the last 20 years (which appears to be what this question is actually about) here is the <a href="http://woodfortrees.org/plot/rss/from:1995/plot/rss/from:1995/trend/plot/uah/from:1995/plot/uah/from:1995/trend/plot/none" rel="nofollow noreferrer">url</a> used to generate it.</p>

<p><a href="https://i.sstatic.net/7jKHM.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/7jKHM.png" alt="enter image description here"></a></p>

<p>As you can see, they disagree quite considerable on the value of the trend.  UAH and RSS are different methods used to infer trophospheric temperatures from them MSU instrument carried aboard various weather satellites.  The reason why they differ is because they use different methods to deal with the various drifts and biases involved in the measurements, and the fact that we don't know exactly how this is best performed is what is known as <em>structural uncertainty</em>.  Note there are a couple of other similar products, but UAH and RSS are the main ones.</p>

<p>As to "no significant warming for over 20 years", this is the subject of a fair bit of discussion in the journals, but not nearly as much as in the blogsphere, and a lot of it stems from not understanding what the term "statistically significant" means (and more importantly, what it doesn't mean).  The key point is that "no significant warming" does not mean "there has been no warming" or that "the rate of warming has slowed".  Unfortunately the reasons for this are a little complicated, so I will start with a simple example.</p>

<p>Consider the usual statistical test for the bias of a coin, we start by stating the null and alternative hypotheses:</p>

<p>$H_0$ - null hypothesis, unbiased coin, probability of a head = p - 0.5.</p>

<p>$H_1$ - alternative hypothesis, biased coin, $p \neq 0.5$.</p>

<p>We then flip the coin $n$ times and count the number of heads, if the p-value is less than some pre-determined value, typically $\alpha = 0.05$, then we say that we can "reject the null hypothesis", implying that the data provides some support for our alternative hypothesis, $H_1$.</p>

<p>However, if we are unable to reject $H_0$, there are at least two reasons for this, it may be that $H_0$ is true, or it may be that $H_0$ is false but we haven't seen enough data yet to be confident of this.  For example, if we only toss the coin four times, then even if we get a head every time, we still won't be able to reject the null hypothesis as the p-value cannot be smaller than 0.0625.  </p>

<p>The <a href="https://en.wikipedia.org/wiki/Statistical_power" rel="nofollow noreferrer"><em>statistical power</em></a> is the probability [in a frequentist sense] that the test correctly rejects the null hypothesis ($H_0$) when the alternative hypothesis ($H_1$) is true.  In this case, the statistical power of the test with only four flips is zero, because we can never reject $H_0$.</p>

<p>So, if you want to claim that it is in some way a surprise that we can't reject the null hypothesis, you need to show that the power of the test is high, and in the case of the trends over the last 20 years, it isn't particularly high, as similar trendless periods ocurr both in the observations and in the model output, as shown by <a href="http://onlinelibrary.wiley.com/doi/10.1029/2009GL037810/abstract" rel="nofollow noreferrer">Easterling and Wehner</a>.  For example the trend in RSS to 1997 is very similar to the trend from 1995 to the present day, and that is almost as long:</p>

<p><a href="https://i.sstatic.net/8oin3.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8oin3.png" alt="enter image description here"></a></p>

<p>Part of the reason for this is that the RSS and UAH datasets are both very sensitive to ENSO, and the trend over the last 20 years is dominated by the 1998 El-Nino.</p>

<p>So how long do you need to get reasonable statistical power?  Well climatologists generally use a period of at least thirty years (IIRC this is a WMO guideline).  <a href="http://onlinelibrary.wiley.com/doi/10.1029/2011JD016263/abstract" rel="nofollow noreferrer">Santer el al</a> performed a study and found that you would need <strong>at least</strong> 17 years of data for identifying human impacts on surface temperatures.  Note this is a bare minimum, and refers to the detection of a trend in a randomly chosen time period.  If you wait until a period of 17 years comes a long before making the argument for a hiatus, the assumptions of that analysis are violated by the fact that multiple hypothesis tests are being implicitly performed, and in practice you would need a much longer period.</p>

<p>Now are scientists ignoring the apparent "hiatus"?  No, there have been many studies analysing it, for instance <a href="http://iopscience.iop.org/article/10.1088/1748-9326/6/4/044022/meta" rel="nofollow noreferrer">Foster and Rahmstorf</a> show that the apparent hiatus can be reasonably explained by ENSO and volcanic forcing, and so there is no real reason to suppose that there has been a pause in anthropogenic global warming, and the apparent hiatus is probably due to a redistribution of heat between the atmosphere and oceans.  There has even been a special issue of <a href="http://www.nature.com/ngeo/journal/v7/n3/full/ngeo2116.html" rel="nofollow noreferrer">Nature Geosciences</a> devoted to this topic.</p>

<p>UPDATE: @user1286792 notes in the comments below: <em>"!UAH, and !RSS show it has been 21.5 years since there has been any tropospheric warming."</em>.  This clearly isn't true, at least for UAH.  If you plot the trend since 1995, it is essentially the same as the long term trend since the start of the dataset.  The fact that the RSS trend for the last 20 years is very different is I suspect the reason skeptic blogs switched from using UAH to RSS, but as always don't believe everything you read on line, and woodfortrees is a great tool for checking things.  As I said, UAH and RSS vary considerably over the last 20 years in their trends and the reason for this is structural uncertainty.  That doesn't mean that either of them are right or wrong and if your argument is not valid for both, then you probably shouldn't be confident that it is true.  Basically the timescale is too short to reliably estimate the trend given the uncertainties in the data, including the structural uncertainties.</p>

<p><a href="https://i.sstatic.net/Oyu6F.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Oyu6F.png" alt="enter image description here"></a></p>

<p>Caveat: I think WFT may be using a previous version of UAH, however this rather illustrates my point about the structural uncertainties, if successive updates to the algorithm make such large differences to the trends, that means the structural uncertainties are very large and we should take that into account when looking at the trends.  However, the basic point remains that (i) the trends are too short to expect the warming to be significant (ii) the apparent haitus is adequately explained by ENSO and volcanic forcing (iii) similar periods of little warming are seen in the output of GCMs, and so it is not entirely unexpected.</p>

CC BY-SA 3.0
2015-11-12T14:26:34.790Z
Thanks for the long careful reply. But my question was over the new UAH 6.0 data which from 1995 has a trend of .0165C/decade. RSS from 1995 has a trend of .0170C/decade. 

And as my original graph shows, the UAH 6.0 and RSS data are nearly always within .2C of each other. And this is remarkable, as if memory serves me, they both claim  a rough accuracy or ~.5C on their individual temperature readings. And it has been **at least** 17 years without statistically significant warming.
FYI UAH plans to deprecate the 5.6 shortly.
RodgerDodger
CC BY-SA 3.0
2015-11-12T15:10:50.620Z
".2C of each other. And this is remarkable," They are both analyses of the same basic measurements, so it is not clear why this should be remarkable.  The approx 0.5C accuracy would include all sources of uncertainty, not just the structural uncertainties.  I suspect that the makers of RSS and UAH are aware of the same basic bias/drift problems and their solutions are similar.  I have already explained why 17 years is a bare minimum, and then only for a randomly selected period.  The apparent hiatus is unusual and interesting, but the lack of statistical significance means very little.
Dikran Marsupial
CC BY-SA 3.0
2015-11-12T20:22:19.847Z
The .2C is remarkable in that more than a few leading authors of SST and ground temp papers have said the MSU/AMSU long term data is unreliable. That they corroborate each other in publicly available peer reviewed results speaks to their veracity. ![UAH](http://postimg.org/image/5iu118uzx/), and ![RSS](http://postimg.org/image/fkwg25v4l/) show it has been 21.5 years since there has been any tropospheric warming.
RodgerDodger
CC BY-SA 3.0
2015-11-12T20:29:30.183Z
I moved the graphs to imgur so they can be viewed side by side: [UAH and RSS](http://imgur.com/a/kCOUz).
RodgerDodger
CC BY-SA 3.0
2015-11-13T07:53:50.650Z
"show it has been 21.5 years since there has been any tropospheric warming" no, that is not true at all.  If nothing else, as you can see form my first figure, UAH clearly shows warming over the last 20 years.  "no significant warming" does not mean "there has been no warming", especially if the start point is cherry picked to maximise the length of the "trendless" period.  This is a misuse of statistics.  Please can you provide a reference to somewhere where authors of papers on surface temperatures have said that the MSU based datasets are unreliable.
Dikran Marsupial
CC BY-SA 3.0
2015-11-13T08:03:14.080Z
@user1286792 see my update above.
Dikran Marsupial
CC BY-SA 3.0
2015-11-13T14:49:35.583Z
You continue to point to outdated data in your graph from above. Let me be clear. That is not the latest UAH data. That is the 5.6 dataset, which is being deprecated. And when you say there has been warming, what you're saying is we have a thermometer which is accurate to +-.5C. And since it now shows +.4C temp increase, you're saying it has clearly gotten warmer. That is not how accuracy works. And nothing was cherry picked. That's simply as far back as you can go from the most current data point and get a zero trend.
RodgerDodger
CC BY-SA 3.0
2015-11-13T15:07:20.760Z
I updated my data to include October. Looks like October pushed up one month the time since statistically significant warming. Not surprising given that El Nino is at near peak. http://imgur.com/a/UzGuQ
RodgerDodger
CC BY-SA 3.0
2015-11-13T15:08:24.897Z
By the way, your answer was very well done.
RodgerDodger
CC BY-SA 3.0
2015-11-13T16:03:40.577Z
"And when you say there has been warming, what you're saying is we have a thermometer which is accurate to +-.5C. And since it now shows +.4C temp increase, you're saying it has clearly gotten warmer."  no, I am not saying that at all (the uncertainty of a trend is not the same thing as the uncertainty of the measurements). " And nothing was cherry picked. That's simply as far back as you can go from the most current data point and get a zero trend. " that ***is*** cherry picking.
Dikran Marsupial
CC BY-SA 3.0
2015-11-13T16:05:37.377Z
Please can you provide a reference to somewhere where authors of papers on surface temperatures have said that the MSU based datasets are unreliable.
Dikran Marsupial
CC BY-SA 3.0
2015-11-13T20:59:34.427Z
Looks like stack exchange doesn't like long draw out discussions. But finding out how long it has been since there has been warming would be the opposite of cherry picking. It is distinctly useful data. Saying there was no warming between 2002 and 2005 would be cherry picking, unless you were studying forcings during that short period. I'll look up the quotes later, and move this to chat as stack exchange recommends.
RodgerDodger
CC BY-SA 3.0
2015-11-14T13:59:31.753Z
@user1286792 choosing the endpoints to maximize the support for  a given argument (e.g. "there has been a hiatus") is exactly what cherry picking is about.  Choosing to look at the data sources that maximize the evidence of a hiatus and ignoring the others is again cherry picking.  Someone wanting to argue for the existence of a hiatus would be better off looking at all of the datasets and using a robust statistical procedure for establishing that the rate of warming had changed (changepoint analysis) if they wanted to avoid cherry picking.
Dikran Marsupial
CC BY-SA 3.0
2015-11-16T15:25:48.010Z
The ground station temps are ... questionable. And SST's are too spread out. We need 10x (or more like 1000x) as many buoys to not need statistical shenanigans to get reliable data. The oceans are far from homogeneous with the same difficulties as the atmosphere. The MSU/AMSU is the best data. And it differs from the less accurate data. That difference is important. 

http://www.surfacestations.org/
RodgerDodger
CC BY-SA 3.0
2015-11-16T18:39:16.737Z
The MSU datasets require just as much adjustments as the surface temperature datasets, note the vary large difference between successive versions of UAH.  If the structural uncertainties in the MSU data were small, then there wouldn't be such large differences between versions as the software would have already ironed out the major issues.  The MSU data also cannot measure surface temperatures, so if you want to know surface temperatures, then I'm afraid you will have to stick with the surface measurements.  All the data are questionable, which is why the scientists are working on it.
Dikran Marsupial
CC BY-SA 3.0
2015-11-16T18:40:31.843Z
Now, please can you provide a reference to somewhere where authors of papers on surface temperatures have said that the MSU based datasets are unreliable (this is the third time I have asked this).
Dikran Marsupial
CC BY-SA 3.0
2015-11-16T20:38:10.860Z
It took me a while to dig up the article I was thinking of and I was wrong. It was Dr. Fuzhong Weng of the NOAA's article on AMSU calibration. I remembered NOAA and thought ground station researcher, which was wrong. Sorry for the confusion and thanks for being so helpful.
RodgerDodger
CC BY-SA 3.0
2015-11-17T08:08:27.390Z
Can you give a link to the article you had in mind?  If someone who actively works on analysing the AMSU data suggests that they are unreliable, then that suggests they are just as "questionable" as the surface instrumental record (as I pointed out). This isn't a problem, as long as you are aware of the issues when looking at the data, and don't assume that any of them are necessarily right (taking a view over all of the datasets is probably best and assume the reality lies in the spread somewhere).
Dikran Marsupial
CC BY-SA 3.0
2015-11-17T19:56:51.907Z
I gave up looking for the exact paper. I remember he said that MSU readings over precipitation could be as much as 30C off and it was published in 2013. Roy Spencer responded to the paper saying that radiosondes had confirmed his AMSU calibrations and he had dealt with this exact issue for decades. Plus there's the RSS closely confirming the UAH data. But here's a link to his publications: http://www.researcherid.com/ProfileView.action?returnCode=ROUTER.Unauthorized&queryString=KG0UuZjN5Wkk5ADZ%252BJIrcYpu7B%252F4lpk8wbP7IzKgGzg%253D&SrcApp=CR&Init=Yes
RodgerDodger
CC BY-SA 3.0
2015-11-19T08:46:27.843Z
Sorry, if you don't have a reference to back up your claim, it is hard to address it.  Note the "over precipitation", which suggests they are talking about local (in both a temporal and spatial sense), and that does not imply that global MSU temperature datasets are considered unreliable.  However without a reference, I can't determine that.  I suspect you have over-interpreted it.  BTW radiosonde data contains plenty of biases and problems as well, which require adjustments.
Dikran Marsupial
CC BY-SA 3.0
2015-11-12T08:38:30.747Z
2015-11-13T08:28:44.760Z
2015-11-13T08:28:44.760Z
Dikran Marsupial
<p>The UAH 6.0 and RSS lower troposphere data sets line up nearly perfectly and both show no significant warming for over 20 years.</p>

<p>What is the leading theory for what's going on? What explains this?</p>

<p><a href="https://i.sstatic.net/Ofs52.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Ofs52.jpg" alt="enter image description here"></a></p>

CC BY-SA 3.0
2015-11-01T06:57:18.150Z
The leading theory is that you are getting your information from kool-aid sites that lie. Please link your claims and your graph to a reputable peer-reviewed scientific journal.
David Hammen
CC BY-SA 3.0
2015-11-01T15:37:33.210Z
I got my data from the actual UAH and RSS data sets.
RodgerDodger
CC BY-SA 3.0
2015-11-01T15:38:44.787Z
RSS TLT: http://images.remss.com/msu/msu_time_series.html 
UAH 6.0 TLT: http://www.nsstc.uah.edu/data/msu/v6.0beta/tlt/tltglhmam_6.0beta3.txt
RodgerDodger
CC BY-SA 3.0
2015-11-01T15:59:42.577Z
And I can't link the graph since I created it. But it is a simple subtraction of the TLT data of UAH from RSS to show they were nearly in perfect agreement. I can post my code if you want to double check the math.
RodgerDodger
CC BY-SA 3.0
2015-11-03T23:52:29.147Z
@DavidHammen The satellite data is publicly accessible. If you wanted to show the OP's question is based on nonsense, the best response would be to link to a plot in a trustworthy source in an answer not to simply accuse him of reading dodgy sources. Then we'd all have learned something useful and this site would be a useful resource for real evidence.
matt_black
CC BY-SA 3.0
2015-11-04T14:23:56.057Z
I've done quite a bit of research since posting this question, and it looks like there are two camps concerning TLT data created from MSU/AMSU's. Those who think it is accurate with the bias corrections used, and those who think they are not accurate. Of those who think it is not accurate, I can't find any peer reviewed research that hasn't already been incorporated into the bias corrections. Maybe someone could help me find why so many believe the data is wrong, other than that it conflicts somewhat with HADCRUT4 and much more with the newer ERSST.v4.
RodgerDodger
CC BY-SA 3.0
2015-11-08T08:20:54.063Z
One explanation is that the theory that co2 makes temeratures rise is incorrect, but this is a very unpopular idea to mention. Anyone care to link to a graph that show co2 lagging temperature for the last few thousand years??
acidohm
CC BY-SA 3.0
2015-11-08T19:58:52.737Z
I've read a lot more about this issue since I posted this question. It appears that even though all the peer peer reviewed critiques of MSU and AMSU as a long term temperature record have been incorporated into both the RSS and UAH records, lots of scientists just don't believe MSU/AMSU's can provide long term records. I can't find an actual paper showing how though.
RodgerDodger
CC BY-SA 3.0
2015-11-09T12:14:16.270Z
It isn't surprising that the trend over the last 20 years is not statistically significant because the statistical power of the test is low.  The satellite datasets seem more strongly affected by ENSO than the surface datasets, so the 1998 El-Nino pretty much explains the apparent "hiatus".  Foster and Rahmstorf showed that the apparent slowdown is well explained by ENSO and volcanic forcings.  There was a special issue in Nature geosciences last year on the "hiatus".  It would be better if your question were more specific about what you want to discuss.
Dikran Marsupial
CC BY-SA 3.0
2015-11-09T12:17:29.353Z
BTW the agreement between UAH and RSS doesn't seem to be that good, and their trends over the last 20 years are very different http://woodfortrees.org/plot/uah/from:1995/plot/uah/from:1995/trend/plot/rss/from:1995/plot/rss/from:1995/trend/plot/none
Dikran Marsupial
CC BY-SA 3.0
2015-11-09T12:22:14.420Z
@user1286792 note that the UAH and RSS datasets are just different ways of processing the same MSU satellite measurements to deal with the various drifts and biases.  As they both give very different trends over the last 20 years, that shows that are significant structural uncertainties in interpreting the raw measurements.  Note also that the TLT datasets are measuring the temperature of the lower trophosphere (a fairly thick layer of the atmosphere) and not the surface, so there is no reason to expect UAH/RSS and HADCRUT4 to be in close agreement.
Dikran Marsupial
CC BY-SA 3.0
2015-11-09T12:30:45.350Z
That CO2 causes temperatures to rise and why has been well understood for over a century, and is supported by a wide range of observations, experiment and theory.  As to CO2 lagging temperature in paleoclimate, this is rather well understood (http://www.skepticalscience.com/co2-lags-temperature.htm), however mining fossil fuels means there is now a way for CO2 to act as a forcing, rather than a feedback.  Neither UAH nor RSS is necessarily right or wrong, both are legitimate interpretations of the data and you should look at both.
Dikran Marsupial
CC BY-SA 3.0
2015-11-09T15:35:46.173Z
Dikran that seems a bit harsh, and I doubt the "CO2 causes temperatures to rise" in the global climate context qualifies as "well understood". And I doubt anyone would argue that CO2 does not absorb thermal radiation. The question is, how does 1/3rd of all man released (anthropogenic) CO2 in the atmosphere get released in the last 20 years, and the UAH/RSS data show no significant change in global temperatures.
RodgerDodger
CC BY-SA 3.0
2015-11-09T15:59:26.673Z
@user1286792 The basic mechanism of the greenhouse mechanism was known by e.g. Ekholm in his paper from 1901, the basic mechanism *is* will understood and has plenty of support from the observations.  What is less well understood is the feedback mechansims that determine the exact value of climate sensitivity and the regional implications.  If that is your question, I suggest that you edit the topic of this page to explain it in more detail.  The rate of warming due to the enhance GHE is small in comparison to the variability caused by things like ENSO on the scale of a decade or so, so ....
Dikran Marsupial
CC BY-SA 3.0
2015-11-09T16:00:37.157Z
there will be occasional periods of little or no warming, this is found in the observations and is prdicted in the model output (although the models can't predict when it will happen as ENSO is chaotic).  See e.g. Easterling and Wehner http://onlinelibrary.wiley.com/doi/10.1029/2009GL037810/abstract
Dikran Marsupial
CC BY-SA 3.0
2015-11-09T19:53:01.733Z
I'm glad you agree with me on what is known and not known about CO2 and its effect on atmospheric temperatures. 

The paper you cite shows a model in the Results section which predicts a monster El Nino in 2015. We aren't having a monster El Nino this year. The model shows a single 10 year period of no warming (which is now 20 years) and predicts a 15 year period of no warming (which isn't happening). With the RSS/UAH data we are over 20 years of statistically insignificant warming. Are you saying the UAH/RSS is valid, but something predicts 20+ years of no warming?
RodgerDodger
CC BY-SA 3.0
2015-11-10T09:40:34.540Z
Where exactly do Easterling and Wehner predict a monster el-nino in 2015?  ENSO is chaotic an unpredictable, the models simulate effects similar to ENSO, but they are not expected to be coherent with ENSO on this planet.  I suspect you have misunderstood something there.
Dikran Marsupial
CC BY-SA 3.0
2015-11-10T09:43:19.280Z
Yes, a 20 year period with little or no warming is not unduly surprising, as clearly stated in the abstract of the paper "We show that the climate over the 21st century can and likely will produce periods of a decade or two where the globally averaged surface air temperature shows no trend or even slight cooling in the presence of longer-term warming."  This is especially true for the satelite datasets, which appear to be much more sensitive to ENSO.  Note that the trend in RSS from 1979 to 1999 wasn't statistically significant either.
Dikran Marsupial
CC BY-SA 3.0
2015-11-10T10:04:04.663Z
Incidentally, there is a pretty substantial El-Nino shaping up at the moment http://www.esrl.noaa.gov/psd/enso/mei/ts.gif (although I suspect that is just a coincidence).
Dikran Marsupial
<climate-change><troposphere>
UAH and RSS Lower Troposphere data
RodgerDodger
# UAH and RSS Lower Troposphere data

(Asked by: username_0 on 2015-10-30)

The UAH 6.0 and RSS lower troposphere data sets line up nearly perfectly and both show no significant warming for over 20 years.

What is the leading theory for what's going on? What explains this?

[![enter image description here](https://i.sstatic.net/Ofs52.jpg)](https://i.sstatic.net/Ofs52.jpg)

**Tags:** climate-change, troposphere

> **Comments:**
> **username_1**: The leading theory is that you are getting your information from kool-aid sites that lie. Please link your claims and your graph to a reputable peer-reviewed scientific journal.  
> **username_0**: I got my data from the actual UAH and RSS data sets.  
> **username_0**: RSS TLT: http://images.remss.com/msu/msu_time_series.html  UAH 6.0 TLT: http://www.nsstc.uah.edu/data/msu/v6.0beta/tlt/tltglhmam_6.0beta3.txt  
> **username_0**: And I can't link the graph since I created it. But it is a simple subtraction of the TLT data of UAH from RSS to show they were nearly in perfect agreement. I can post my code if you want to double check the math.  
> **username_2**: @username_1 The satellite data is publicly accessible. If you wanted to show the OP's question is based on nonsense, the best response would be to link to a plot in a trustworthy source in an answer not to simply accuse him of reading dodgy sources. Then we'd all have learned something useful and this site would be a useful resource for real evidence.  
> **username_0**: I've done quite a bit of research since posting this question, and it looks like there are two camps concerning TLT data created from MSU/AMSU's. Those who think it is accurate with the bias corrections used, and those who think they are not accurate. Of those who think it is not accurate, I can't find any peer reviewed research that hasn't already been incorporated into the bias corrections. Maybe someone could help me find why so many believe the data is wrong, other than that it conflicts somewhat with HADCRUT4 and much more with the newer ERSST.v4.  
> **username_3**: One explanation is that the theory that co2 makes temeratures rise is incorrect, but this is a very unpopular idea to mention. Anyone care to link to a graph that show co2 lagging temperature for the last few thousand years??  
> **username_0**: I've read a lot more about this issue since I posted this question. It appears that even though all the peer peer reviewed critiques of MSU and AMSU as a long term temperature record have been incorporated into both the RSS and UAH records, lots of scientists just don't believe MSU/AMSU's can provide long term records. I can't find an actual paper showing how though.  
> **username_4**: It isn't surprising that the trend over the last 20 years is not statistically significant because the statistical power of the test is low.  The satellite datasets seem more strongly affected by ENSO than the surface datasets, so the 1998 El-Nino pretty much explains the apparent "hiatus".  Foster and Rahmstorf showed that the apparent slowdown is well explained by ENSO and volcanic forcings.  There was a special issue in Nature geosciences last year on the "hiatus".  It would be better if your question were more specific about what you want to discuss.  
> **username_4**: BTW the agreement between UAH and RSS doesn't seem to be that good, and their trends over the last 20 years are very different http://woodfortrees.org/plot/uah/from:1995/plot/uah/from:1995/trend/plot/rss/from:1995/plot/rss/from:1995/trend/plot/none  
> **username_4**: @user1286792 note that the UAH and RSS datasets are just different ways of processing the same MSU satellite measurements to deal with the various drifts and biases.  As they both give very different trends over the last 20 years, that shows that are significant structural uncertainties in interpreting the raw measurements.  Note also that the TLT datasets are measuring the temperature of the lower trophosphere (a fairly thick layer of the atmosphere) and not the surface, so there is no reason to expect UAH/RSS and HADCRUT4 to be in close agreement.  
> **username_4**: That CO2 causes temperatures to rise and why has been well understood for over a century, and is supported by a wide range of observations, experiment and theory.  As to CO2 lagging temperature in paleoclimate, this is rather well understood (http://www.skepticalscience.com/co2-lags-temperature.htm), however mining fossil fuels means there is now a way for CO2 to act as a forcing, rather than a feedback.  Neither UAH nor RSS is necessarily right or wrong, both are legitimate interpretations of the data and you should look at both.  
> **username_0**: username_4 that seems a bit harsh, and I doubt the "CO2 causes temperatures to rise" in the global climate context qualifies as "well understood". And I doubt anyone would argue that CO2 does not absorb thermal radiation. The question is, how does 1/3rd of all man released (anthropogenic) CO2 in the atmosphere get released in the last 20 years, and the UAH/RSS data show no significant change in global temperatures.  
> **username_4**: @user1286792 The basic mechanism of the greenhouse mechanism was known by e.g. Ekholm in his paper from 1901, the basic mechanism *is* will understood and has plenty of support from the observations.  What is less well understood is the feedback mechansims that determine the exact value of climate sensitivity and the regional implications.  If that is your question, I suggest that you edit the topic of this page to explain it in more detail.  The rate of warming due to the enhance GHE is small in comparison to the variability caused by things like ENSO on the scale of a decade or so, so ....  
> **username_4**: there will be occasional periods of little or no warming, this is found in the observations and is prdicted in the model output (although the models can't predict when it will happen as ENSO is chaotic).  See e.g. Easterling and Wehner http://onlinelibrary.wiley.com/doi/10.1029/2009GL037810/abstract  
> **username_0**: I'm glad you agree with me on what is known and not known about CO2 and its effect on atmospheric temperatures.   The paper you cite shows a model in the Results section which predicts a monster El Nino in 2015. We aren't having a monster El Nino this year. The model shows a single 10 year period of no warming (which is now 20 years) and predicts a 15 year period of no warming (which isn't happening). With the RSS/UAH data we are over 20 years of statistically insignificant warming. Are you saying the UAH/RSS is valid, but something predicts 20+ years of no warming?  
> **username_4**: Where exactly do Easterling and Wehner predict a monster el-nino in 2015?  ENSO is chaotic an unpredictable, the models simulate effects similar to ENSO, but they are not expected to be coherent with ENSO on this planet.  I suspect you have misunderstood something there.  
> **username_4**: Yes, a 20 year period with little or no warming is not unduly surprising, as clearly stated in the abstract of the paper "We show that the climate over the 21st century can and likely will produce periods of a decade or two where the globally averaged surface air temperature shows no trend or even slight cooling in the presence of longer-term warming."  This is especially true for the satelite datasets, which appear to be much more sensitive to ENSO.  Note that the trend in RSS from 1979 to 1999 wasn't statistically significant either.  
> **username_4**: Incidentally, there is a pretty substantial El-Nino shaping up at the moment http://www.esrl.noaa.gov/psd/enso/mei/ts.gif (although I suspect that is just a coincidence).  

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## 1 answers

### Answer by username_4 on 2015-11-12. Score: 4 | Accepted answer

Firstly, the RSS and UAH datasets do not "line up nearly perfectly", the diagram below shows both products over the last 20 years (which appears to be what this question is actually about) here is the [url](http://woodfortrees.org/plot/rss/from:1995/plot/rss/from:1995/trend/plot/uah/from:1995/plot/uah/from:1995/trend/plot/none) used to generate it.

[![enter image description here](https://i.sstatic.net/7jKHM.png)](https://i.sstatic.net/7jKHM.png)

As you can see, they disagree quite considerable on the value of the trend. UAH and RSS are different methods used to infer trophospheric temperatures from them MSU instrument carried aboard various weather satellites. The reason why they differ is because they use different methods to deal with the various drifts and biases involved in the measurements, and the fact that we don't know exactly how this is best performed is what is known as *structural uncertainty*. Note there are a couple of other similar products, but UAH and RSS are the main ones.

As to "no significant warming for over 20 years", this is the subject of a fair bit of discussion in the journals, but not nearly as much as in the blogsphere, and a lot of it stems from not understanding what the term "statistically significant" means (and more importantly, what it doesn't mean). The key point is that "no significant warming" does not mean "there has been no warming" or that "the rate of warming has slowed". Unfortunately the reasons for this are a little complicated, so I will start with a simple example.

Consider the usual statistical test for the bias of a coin, we start by stating the null and alternative hypotheses:

$H\_0$ - null hypothesis, unbiased coin, probability of a head = p - 0.5.

$H\_1$ - alternative hypothesis, biased coin, $p \neq 0.5$.

We then flip the coin $n$ times and count the number of heads, if the p-value is less than some pre-determined value, typically $\alpha = 0.05$, then we say that we can "reject the null hypothesis", implying that the data provides some support for our alternative hypothesis, $H\_1$.

However, if we are unable to reject $H\_0$, there are at least two reasons for this, it may be that $H\_0$ is true, or it may be that $H\_0$ is false but we haven't seen enough data yet to be confident of this. For example, if we only toss the coin four times, then even if we get a head every time, we still won't be able to reject the null hypothesis as the p-value cannot be smaller than 0.0625.

The [*statistical power*](https://en.wikipedia.org/wiki/Statistical_power) is the probability [in a frequentist sense] that the test correctly rejects the null hypothesis ($H\_0$) when the alternative hypothesis ($H\_1$) is true. In this case, the statistical power of the test with only four flips is zero, because we can never reject $H\_0$.

So, if you want to claim that it is in some way a surprise that we can't reject the null hypothesis, you need to show that the power of the test is high, and in the case of the trends over the last 20 years, it isn't particularly high, as similar trendless periods ocurr both in the observations and in the model output, as shown by [Easterling and Wehner](http://onlinelibrary.wiley.com/doi/10.1029/2009GL037810/abstract). For example the trend in RSS to 1997 is very similar to the trend from 1995 to the present day, and that is almost as long:

[![enter image description here](https://i.sstatic.net/8oin3.png)](https://i.sstatic.net/8oin3.png)

Part of the reason for this is that the RSS and UAH datasets are both very sensitive to ENSO, and the trend over the last 20 years is dominated by the 1998 El-Nino.

So how long do you need to get reasonable statistical power? Well climatologists generally use a period of at least thirty years (IIRC this is a WMO guideline). [Santer el al](http://onlinelibrary.wiley.com/doi/10.1029/2011JD016263/abstract) performed a study and found that you would need **at least** 17 years of data for identifying human impacts on surface temperatures. Note this is a bare minimum, and refers to the detection of a trend in a randomly chosen time period. If you wait until a period of 17 years comes a long before making the argument for a hiatus, the assumptions of that analysis are violated by the fact that multiple hypothesis tests are being implicitly performed, and in practice you would need a much longer period.

Now are scientists ignoring the apparent "hiatus"? No, there have been many studies analysing it, for instance [Foster and Rahmstorf](http://iopscience.iop.org/article/10.1088/1748-9326/6/4/044022/meta) show that the apparent hiatus can be reasonably explained by ENSO and volcanic forcing, and so there is no real reason to suppose that there has been a pause in anthropogenic global warming, and the apparent hiatus is probably due to a redistribution of heat between the atmosphere and oceans. There has even been a special issue of [Nature Geosciences](http://www.nature.com/ngeo/journal/v7/n3/full/ngeo2116.html) devoted to this topic.

UPDATE: @user1286792 notes in the comments below: *"!UAH, and !RSS show it has been 21.5 years since there has been any tropospheric warming."*. This clearly isn't true, at least for UAH. If you plot the trend since 1995, it is essentially the same as the long term trend since the start of the dataset. The fact that the RSS trend for the last 20 years is very different is I suspect the reason skeptic blogs switched from using UAH to RSS, but as always don't believe everything you read on line, and woodfortrees is a great tool for checking things. As I said, UAH and RSS vary considerably over the last 20 years in their trends and the reason for this is structural uncertainty. That doesn't mean that either of them are right or wrong and if your argument is not valid for both, then you probably shouldn't be confident that it is true. Basically the timescale is too short to reliably estimate the trend given the uncertainties in the data, including the structural uncertainties.

[![enter image description here](https://i.sstatic.net/Oyu6F.png)](https://i.sstatic.net/Oyu6F.png)

Caveat: I think WFT may be using a previous version of UAH, however this rather illustrates my point about the structural uncertainties, if successive updates to the algorithm make such large differences to the trends, that means the structural uncertainties are very large and we should take that into account when looking at the trends. However, the basic point remains that (i) the trends are too short to expect the warming to be significant (ii) the apparent haitus is adequately explained by ENSO and volcanic forcing (iii) similar periods of little warming are seen in the output of GCMs, and so it is not entirely unexpected.

> **Comments:**
> **username_0**: Thanks for the long careful reply. But my question was over the new UAH 6.0 data which from 1995 has a trend of .0165C/decade. RSS from 1995 has a trend of .0170C/decade.   And as my original graph shows, the UAH 6.0 and RSS data are nearly always within .2C of each other. And this is remarkable, as if memory serves me, they both claim  a rough accuracy or ~.5C on their individual temperature readings. And it has been **at least** 17 years without statistically significant warming. FYI UAH plans to deprecate the 5.6 shortly.  
> **username_4**: ".2C of each other. And this is remarkable," They are both analyses of the same basic measurements, so it is not clear why this should be remarkable.  The approx 0.5C accuracy would include all sources of uncertainty, not just the structural uncertainties.  I suspect that the makers of RSS and UAH are aware of the same basic bias/drift problems and their solutions are similar.  I have already explained why 17 years is a bare minimum, and then only for a randomly selected period.  The apparent hiatus is unusual and interesting, but the lack of statistical significance means very little.  
> **username_0**: The .2C is remarkable in that more than a few leading authors of SST and ground temp papers have said the MSU/AMSU long term data is unreliable. That they corroborate each other in publicly available peer reviewed results speaks to their veracity. ![UAH](http://postimg.org/image/5iu118uzx/), and ![RSS](http://postimg.org/image/fkwg25v4l/) show it has been 21.5 years since there has been any tropospheric warming.  
> **username_0**: I moved the graphs to imgur so they can be viewed side by side: [UAH and RSS](http://imgur.com/a/kCOUz).  
> **username_4**: "show it has been 21.5 years since there has been any tropospheric warming" no, that is not true at all.  If nothing else, as you can see form my first figure, UAH clearly shows warming over the last 20 years.  "no significant warming" does not mean "there has been no warming", especially if the start point is cherry picked to maximise the length of the "trendless" period.  This is a misuse of statistics.  Please can you provide a reference to somewhere where authors of papers on surface temperatures have said that the MSU based datasets are unreliable.  
> **username_4**: @user1286792 see my update above.  
> **username_0**: You continue to point to outdated data in your graph from above. Let me be clear. That is not the latest UAH data. That is the 5.6 dataset, which is being deprecated. And when you say there has been warming, what you're saying is we have a thermometer which is accurate to +-.5C. And since it now shows +.4C temp increase, you're saying it has clearly gotten warmer. That is not how accuracy works. And nothing was cherry picked. That's simply as far back as you can go from the most current data point and get a zero trend.  
> **username_0**: I updated my data to include October. Looks like October pushed up one month the time since statistically significant warming. Not surprising given that El Nino is at near peak. http://imgur.com/a/UzGuQ  
> **username_0**: By the way, your answer was very well done.  
> **username_4**: "And when you say there has been warming, what you're saying is we have a thermometer which is accurate to +-.5C. And since it now shows +.4C temp increase, you're saying it has clearly gotten warmer."  no, I am not saying that at all (the uncertainty of a trend is not the same thing as the uncertainty of the measurements). " And nothing was cherry picked. That's simply as far back as you can go from the most current data point and get a zero trend. " that ***is*** cherry picking.  
> **username_4**: Please can you provide a reference to somewhere where authors of papers on surface temperatures have said that the MSU based datasets are unreliable.  
> **username_0**: Looks like stack exchange doesn't like long draw out discussions. But finding out how long it has been since there has been warming would be the opposite of cherry picking. It is distinctly useful data. Saying there was no warming between 2002 and 2005 would be cherry picking, unless you were studying forcings during that short period. I'll look up the quotes later, and move this to chat as stack exchange recommends.  
> **username_4**: @user1286792 choosing the endpoints to maximize the support for  a given argument (e.g. "there has been a hiatus") is exactly what cherry picking is about.  Choosing to look at the data sources that maximize the evidence of a hiatus and ignoring the others is again cherry picking.  Someone wanting to argue for the existence of a hiatus would be better off looking at all of the datasets and using a robust statistical procedure for establishing that the rate of warming had changed (changepoint analysis) if they wanted to avoid cherry picking.  
> **username_0**: The ground station temps are ... questionable. And SST's are too spread out. We need 10x (or more like 1000x) as many buoys to not need statistical shenanigans to get reliable data. The oceans are far from homogeneous with the same difficulties as the atmosphere. The MSU/AMSU is the best data. And it differs from the less accurate data. That difference is important.   http://www.surfacestations.org/  
> **username_4**: The MSU datasets require just as much adjustments as the surface temperature datasets, note the vary large difference between successive versions of UAH.  If the structural uncertainties in the MSU data were small, then there wouldn't be such large differences between versions as the software would have already ironed out the major issues.  The MSU data also cannot measure surface temperatures, so if you want to know surface temperatures, then I'm afraid you will have to stick with the surface measurements.  All the data are questionable, which is why the scientists are working on it.  
> **username_4**: Now, please can you provide a reference to somewhere where authors of papers on surface temperatures have said that the MSU based datasets are unreliable (this is the third time I have asked this).  
> **username_0**: It took me a while to dig up the article I was thinking of and I was wrong. It was Dr. Fuzhong Weng of the NOAA's article on AMSU calibration. I remembered NOAA and thought ground station researcher, which was wrong. Sorry for the confusion and thanks for being so helpful.  
> **username_4**: Can you give a link to the article you had in mind?  If someone who actively works on analysing the AMSU data suggests that they are unreliable, then that suggests they are just as "questionable" as the surface instrumental record (as I pointed out). This isn't a problem, as long as you are aware of the issues when looking at the data, and don't assume that any of them are necessarily right (taking a view over all of the datasets is probably best and assume the reality lies in the spread somewhere).  
> **username_0**: I gave up looking for the exact paper. I remember he said that MSU readings over precipitation could be as much as 30C off and it was published in 2013. Roy Spencer responded to the paper saying that radiosondes had confirmed his AMSU calibrations and he had dealt with this exact issue for decades. Plus there's the RSS closely confirming the UAH data. But here's a link to his publications: http://www.researcherid.com/ProfileView.action?returnCode=ROUTER.Unauthorized&queryString=KG0UuZjN5Wkk5ADZ%252BJIrcYpu7B%252F4lpk8wbP7IzKgGzg%253D&SrcApp=CR&Init=Yes  
> **username_4**: Sorry, if you don't have a reference to back up your claim, it is hard to address it.  Note the "over precipitation", which suggests they are talking about local (in both a temporal and spatial sense), and that does not imply that global MSU temperature datasets are considered unreliable.  However without a reference, I can't determine that.  I suspect you have over-interpreted it.  BTW radiosonde data contains plenty of biases and problems as well, which require adjustments.  

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