Thursday, January 7, 2010

Twelve Year Global Satellite + HadCRUT3 Temp Trends


(click to enlarge)

When one presents a chart showing that there has been no global warming for the past 12 years, one can expect that the AGW alarmists will be . . . well, alarmed. As a result, we can expect that the total arsenal of "you can't believe your lying eyes" type of rationalizations will be brought forth in an effort to show that it doesn't matter what the data says. Their arguments fall into two types, and so I will try to deal with them here.

The first argument claims that the starting point for the data has been cherry picked, and therefore proves nothing. Let me mention at this point that last year the argument was also used that the end point was cherry picked because the data ended in a La Nina. This year the data ends in an El Nino, and the trend is still flat. So that argument has been disposed of by time.

The alarmists objection typically asks why an earlier or later starting point was not used. I think that we have to answer that question in respect to the question that we are trying to answer in producing such a chart. The question that I want to answer is "how long has the global temperature trend been flat". If I choose a date before 1998 I am not answering that question. I know already that the temperature was rising before 1998. I am not trying to debate that point. And I know that if I use data from before 1998 that I will get a positive slope. But I'm not making the statement that temperature has been flat for 15 years or 20 years. I'm making the statement that it has been flat for 12 years.

Then the question is asked, "why did you start with an El Nino year and not with 1999 or 2000". This is actually a relevant question, because 1998 was strongly effected by an El Nino that would serve to lower the slope of the trend. In other words, if I cut off 1998, my trend goes positive. But what all of the alarmists choose to ignore is that there were 8 ENSO events in that 12 year time period (5 El Ninos and 3 La Ninas) and that one has to consider them all to decide if the flat trend is actually just and ENSO artifact. So while the 1998 El Nino exercises a strong influence on the slope, one can't simply overlook the fact that the 98 El Nino was followed, only 3 month later, by a La Nina that lasted over two years. The effect of those two events at the beginning of the chart on the slope of the trend basically cancels out. I show how the ENSO events effect the slope here.

But, all things considered we should be able to answer all of the ENSO related starting point issues by simply using an ENSO corrected chart. Last year, Gavin Schmidt, from Real Climate, produced such an ENSO corrected product for the HadCrut3 global data set. I plotted the data here:

The profound effect of the ENSO correction can be seen at the beginning of the chart where the 98 El Nino is brought way down. But as the chart shows, with corrections for all ENSO events accounted for, the remaining trend was still basically flat. Furthermore, the difference between the trend lines for the ENSO corrected data and the non corrected data is tiny. The ENSO corrected chart should put to rest any arguments that the starting point is cherry picked to gain the benefit of a powerful ENSO year. But you can bet that the alarmist will still try to find a way to support that misconception.

The second part of the argument that alarmists present against this kind of chart is that it is not statistically significant. In other words, we cannot say that the trend lines shown in the chart represent the true trend with 95% certainty. This argument is a straw man for more than one reason. We are not trying to present the new trend line as being the new trend with 95% certainty. We are simply saying that there has been no warming for the past 12 years. The argument against such a short period of time is that the variability around the trend is too large to give the trend meaning. That is fine as an argument if you don't look at the physical reasons behind the argument. Climate has large elements of variability over the shorter time period. These are things like ENSO, PDO, AMO, solar, volcanoes, aerosols, etc. But we know what all of these things are, and we can investigate how they effect our chart using things like the ENSO corrected data that I used above. By the way, that correction removed much of the variability, thereby shortening the time period needed for significance. The problem with the current 12 year flat trend is that it cannot be explained by natural elements of variability. I have asked the alarmists, like Gavin Schmidt, many time, to explain the elements of natural variability that were overriding the CO2 signal. But they have no answer.

This means that the answer is one of two things. Either the forcing expected from CO2 is too large, or there are elements of natural variation that are very strong and that are not accounted for by current climate knowledge. If the later is true, then those elements of variation are also not accounted for in the models.

17 comments:

John said...

Trend is flat because you start it in 1998. If you tarted the graph in the 1970s you;d see that the trend is all up, and that this year is warmer than every year in the 19070s, 1980s and up to 98.

John said...

Since we've been directly measuring temperature since about 1650 (for southern England) it's just not a very useful thing to say 'I am only interested in the temperature since 1998'. If it were true that the earth hasn't warmed since 1998 (which it isn't), it would still be like saying 'It's always dark, I know this because I have data from 12 midnight-2am this morning.'

Where I live in south-eastern Australia rainfall is about 30% down on historical norms since about 1998, but if I only had figures since then I wouldn't know there was anything amiss. As it is I do have previous data (plus lots of now dying street trees planted in wetter times and other signs).

Oh, and this drying is caused by global warming, which is anthropogenic, of course.

Tilo Reber said...

John:

I have an explanation for most of your objections above.

John:
If it were true that the earth hasn't warmed since 1998 (which it isn't),

John, what is your evidence that the earth has warmed since 1998?

Anonymous said...

John might also ask Kevin Trenberth why he calls the diverging CO2 and temp. curves over this same time period a "travesty".

J.Peden

Sceptical said...

John: [i]but if I only had figures since then I wouldn't know there was anything amiss[/]That's exactly the point.
'Nothing' has happened the last 12 years, although CO2 concentration has gone up more than 20 ppm in those 12 years. (ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_annmean_mlo.txt)

So, what's going on then? What forces are (at the moment) stronger than Public Enemy CO2?

Henry Galt said...

John wont be back.

Great article Tilo, I will be linking to it.

Thank you.

Slioch said...

You provide graphs of the UAH and RSS global average temperature series, so let us look at the five year average global temperature anomalies from those series. Using five year averages helps to smooth out the shorter-term variations, making it easier to detect trends.
Here is the data;

Years.......UAH......RSS
1980-1984 -0.047C -0.060C
1985-1989 -0.050C -0.070C
1990-1994 -0.032C -0.022C
1995-1999 +0.147C +0.189C
2000-2004 +0.203C +0.254C
2005-2009 +0.238C +0.263C

Do you agree that that information is correct (ie it provides correct UAH & RSS data)?
Do you agree that it shows continued warming, albeit at a lower rate recently than previously?

Tilo Reber said...

Let's break your table into two chunks. The first four lines are of no importance to this post. No skeptic is arguing the fact that it warmed up to 1998. The next two lines show an increase between them because the first line is an artifact of the 1999, 2000 La Nina. I have explained, in great detail, why you cannot do that in the text of my post, as well as in the new post here:
http://reallyrealclimate.blogspot.com/2010/01/another-inconvient-truth-for-agw.html

So, if you want to compare those two 5 year pieces, then get an ENSO corrected version of them and show me what you have.

Slioch said...

Tilo Reber Jan 11 8:22pm

So, having started your article with graphs constructed with raw data from UAH and RSS, you now object to me showing that raw data?

As I explained above, using five year averages helps to remove the noise of inter annual variations in average global temperatures caused by relatively short term events such as ENSOs and volcanic eruptions It is a rough and ready method of removing such noise from the temperature series.

If you want a clearer indication of why the last decade or so does not represent a statistically significant change in slope for the UAH and RSS data then you should consult:

http://tamino.wordpress.com/2009/12/07/riddle-me-this/#more-2108

There, both the UAH and RSS data are plotted: in neither case is the best linear fit and limits of two standard deviations either side of it (established before the year 2000) exceeded by the data after 2000.

Finally, you attempt to justify your use of the data starting in 1998 by claiming that you are merely interested in "how long has the global temperature trend been flat". That is a rather bizarre metric, but if you insist on using it, why have you not made a similar measurement throughout ALL of the UAH and RSS data series? Why have you not shown us the length of other flat periods within that data set? Why do you just cherry-pick the latest period of flat trend and ignore any of the others?

Tilo Reber said...

Slioch:

You give absolutely no evidence of having read the article for this post or for having read the article for the post that I linked in my last comment. I don't mind debating someone on my views, but debating someone with their fingers in their ears is a waste of my time. I'm going to explain it one more time. Go and look at my chart on this post. Click on it to expand it. Then look at the ENSO periods at the top. See the 99 and 00 La Nina's. See their effect on the temperature. Remember also that the ENSO effect is delayed by 3 or 4 month. Your first five year period is an ENSO artifact when it is compared to the second five year period. Your five year period is simply not enough to remove the ENSO effect. In fact, my twelve year period is often not enough either. That is why I have an ENSO corrected chart. Also, don't bother me with links to Tamino. I have answers for Tamino, as do many other people, but he will not post our comments. Tamino is a statistical sophist that runs a propaganda site - plain and simple.

"There, both the UAH and RSS data are plotted: in neither case is the best linear fit and limits of two standard deviations either side of it (established before the year 2000) exceeded by the data after 2000."

Again, look at the starting point. It is in the depth of a La Nina. Of course the trend is up from there. Again, Tamino's demonstration depends on an ENSO artifact. The argument that 1998 also produces an ENSO artifact would be true if it were not followed immediately by a long La Nina. As it is, the two cancel each other out. That is why 1998 is a legitimate place to start while 99 and 00 are not. But you can end the whole argument by using ENSO corrected data, like I have. And the ENSO corrected data still shows no trend.

"why have you not made a similar measurement throughout ALL of the UAH and RSS data series? Why have you not shown us the length of other flat periods within that data set?"

Again you are showing that you want nothing more than to spout the common misconceptions that were fed to you by RC and Tamino. I did exactly what you asked for in the post that I linked for you here:

http://reallyrealclimate.blogspot.com/2010/01/another-inconvient-truth-for-agw.html

I showed that two such periods were natural variation artifacts. One was an ENSO artifact and the other was a volcano artifact. The current 12 year flat trend is not an artifact of anything. That is why it is so significant.

Now if you want to continue this discussion, then at least show that you understand what I have already written in the articles. You don't have to agree. But at least begin by comprehending.

Slioch said...

Tilo Reber January 12 9:08 AM

Well, your one legitimate complaint against me is that I hadn't finished reading your Jan 11th post: your first three paragraphs there are little better than a rant, and I've read far too many of those. So, as I was short of time, that’s as far as I got.

If you want people to consider what you say, please cut out the "stampede the population of the earth, for UN profit", "climategate decline hiders from the CRU", "torture the data into confession", "filled their own coffers with research grants" etc etc. It is difficult to take anyone seriously with that sort of garbage flying around.

Before I get to some of the issues that have arisen already, let me draw your attention to one thing that puzzles me with respect to "ENSO adjusted data". (I've not seen this discussed elsewhere – maybe it has been.) If you look at the graphs of ENSO adjusted versus raw data (eg any of your Jan 11 figs 1- 4) what is striking is their similarity. In every single case the ENSO adjusted data is simply a somewhat damped version of the raw data – every peak and trough in the raw data is replicated in the ENSO adjusted data, though usually not so extremely. Why should that be? If an El Nino is responsible for a peak in global temperatures, then why should one expect a peak, albeit smaller, in global temperatures in the absence of an El Nino? The inescapable conclusion is that one should not, and that therefore the ENSO adjusted figures do NOT show what the global average temperatures would have been in the absence of El Nino/La Nina episodes.

I appreciate you are not responsible for the ENSO adjusted figures, but you ARE using them as if they showed what average global temperatures would be in the absence of El Nino/La Nina episodes. It seems to me that that cannot be justified, and if that is correct then your entire assumption that you have removed their impact on the temperature graphs you show comes crashing to the ground. All you have shown is that if you mute the effects of El Nino/La Nina episodes somewhat then, for example, the almost zero slope of the temperature graph since 1998 does not disappear.

In short, you have assumed the ENSO adjusted figures are really what they say they are. I really cannot see how that can be the case.

A more general statement of the same thing is this: the ENSO adjusted temperature graph is still very noisy. Clearly, that noise cannot be attributed to rapidly varying levels of IR absorption by greenhouse gases in the atmosphere. In other words, the noise is caused by something else (even if it isn’t El Nino/La Nina episodes), but with respect to the signal it is still noise. Therefore, the fact that the signal is masked by the noise for extended periods is still inevitable: that is what happens when your data consists of signal plus noise. The lack of positive trend does not show that the signal has gone away.

I've gone on about that longer than intended, so very briefly:

1. It would not matter if Tamino were a serial murderer: the graphs to which I linked (eg. http://tamino.files.wordpress.com/2009/12/uah2.jpg?w=500&h=325)
would still demand explanation. Merely dismissing them with a few ad hominems isn't good enough. And besides, if they did start in a La Nina episode (as I think you state) then that would increase the slope and make it more, not less, difficult for the last decade to fit into the pre-2000 trend lines. Those graphs shows that there has been no statistically significant change in trend since 2000.

2. As far as the use of raw or ENSO adjusted figures for the last decade (eg my UAH figures) is concerned, since such evidence you provide (from HADCRUT3) shows very little difference between trends, I cannot see that it makes much difference using the five year data either.

Tilo Reber said...

Slioch:
"If you look at the graphs of ENSO adjusted versus raw data (eg any of your Jan 11 figs 1- 4) what is striking is their similarity. In every single case the ENSO adjusted data is simply a somewhat damped version of the raw data – every peak and trough in the raw data is replicated in the ENSO adjusted data, though usually not so extremely. Why should that be? If an El Nino is responsible for a peak in global temperatures, then why should one expect a peak, albeit smaller, in global temperatures in the absence of an El Nino? The inescapable conclusion is that one should not, and that therefore the ENSO adjusted figures do NOT show what the global average temperatures would have been in the absence of El Nino/La Nina episodes."

Well, at least you looked at the data. But your conclusion is not so inescapable. ENSO is an element of variation that runs for periods - roughly speaking - of 4 months to 4 years. During that time the transition into and out of the ENSO is somewhat gradual. Take a look at this:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

But there are other, higher frequency, elements of natural variation still in the data. So what you see is exactly what you would expect from filtering out ENSO. I suggest you read Thompson's paper. He talks about how it all works. Also, Gavin has used Thompson's method to produce an ENSO corrected GISS data set. So you can probably get better details of how it works from him.

"The lack of positive trend does not show that the signal has gone away."

High frequency elements of natural variation are not going to make the signal go away or even disguise it. So you can leave them there and still see what the real trend is. Thompson talks about at least one other high frequency element of variation. And he shows a graph of it. But I'm sure that Thompson doesn't cover them all.

"It would not matter if Tamino were a serial murderer:"

No it wouldn't. But it does matter if he doesn't take contrary views. You can't assume that what your read there is correct when no one is allowed to challenge.

"And besides, if they did start in a La Nina episode (as I think you state) then that would increase the slope and make it more, not less, difficult for the last decade to fit into the pre-2000 trend lines. Those graphs shows that there has been no statistically significant change in trend since 2000."

I'm not sure what you are talking about here. If you start with a La Nina at the beginning of a trend line, then you are going to make the slope of that trend line go up. In regards to the pre 2000 period, there was plenty of warming going on in the 90s. So you don't have to worry about a comparison with the first five years of 2000.

"since such evidence you provide (from HADCRUT3) shows very little difference between trends, I cannot see that it makes much difference using the five year data either."

Actually, if you start both your adjusted and unadjusted periods in 99 or 2000 you will see a lot of difference in the trends. It is just incidental that starting in 1998 gives you a fair balance of influences when using unadjusted data.

Anonymous said...

http://www.ncdc.noaa.gov/oa/climate/...ull-report.pdf

"The trend in the ENSO-related component for 1999–2008 is +0.08±0.07°C decade–1, fully accounting for the overall observed trend. The trend after removing ENSO (the "ENSO-adjusted" trend) is 0.00°±0.05°C decade–1, implying much greater disagreement with anticipated global temperature rise."

You can start in 1999 and the trend is still flat. The silly "but you're starting in 98!" argument goes away.

Tilo Reber said...

You can start in 1999 and the trend is still flat. The silly "but you're starting in 98!" argument goes away.

Thanks anonymous. Your point is the same one that I make in my most recent post - namely - stop arguing about starting points and look at the ENSO corrected data. Then you can start any time you want and the trend will be flat. Of course you can't start before 1998 because we freely admit that temperatures were rising before 1998.

Unfortunately, your link doesn't work and I'd love to have it. Can you give it another shot please.

Chris said...

Slioch said...

Tilo Reber January 12 9:08 AM

Well, your one legitimate complaint against me is that I hadn't finished reading your Jan 11th post: your first three paragraphs there are little better than a rant, and I've read far too many of those. So, as I was short of time, that’s as far as I got.

I went back and reread the first three paragraphs and I still don't see a "rant". Seems like a justification for how the graph was assembled to counter future questions (which John promptly ignored). To me a rant includes ad hominens - didn't see it.

Loke the post BTW

Anonymous said...

No I think the common response would be, "why don't you get the same graph as the experts get?" http://www.cru.uea.ac.uk/cru/data/temperature/nhshgl.gif

Once you get the training to see why you are horribly wrong, then maybe people will start to listen to you.

Tilo Reber said...

Anonymous:
"No I think the common response would be, "why don't you get the same graph as the experts get?""

Eh, because I'm plotting their data since 1998 - the time period that I'm making a statement about. You are linking the time period since 1850. Now why would I want a 160 year chart to find the trend since 1998.

Was that a serious question?