Consistent With Chronicles: A New Record
August 19th, 2008Posted by: Roger Pielke, Jr.
As we’ve documented here on many occasions, some climate scientists like to assert that recent observations of weather and short-term climate are “consistent with” predictions from climate models (see also this essay).
A lot of attention has been paid to recent global average temperature trends, because they have not shown an increase since 1998, 2000, or 2001 (to pick three years often cited in such discussions). An Australian newspaper recently commented on this:
A careful analysis of global temperature graphs from each of the measurement agencies confirm that – despite variations between them – there has not been any notable warming since 2000. Depending on which graphs you use, global temperatures since 2000 have been more or less flat. Some, such as the GISS data, show a modest rise, while others show negligible movement and even a small fall in recent years.
Sceptics like to use graphs that date from 1998 because that was the hottest year on record due to El Nino influences and therefore the temperature trends for the decade look flattest when 1998 is the starting point.
But ultimately this is a phony war because most mainstream scientists do not dispute that global temperatures have remained relatively flat during the past decade. Where they differ with the sceptics is on how this outcome should be interpreted.
“The changes in temperature over the past 10 years have basically plateaued,” says Andy Pitman, co-director of the Climate Change Research Centre at the University of NSW. “But scientists did not anticipate a gradual year-by-year warming in temperature. What matters is the long-term trend. This outcome does not change any of the science but it does change the spin climate deniers can put on it.”
What I found most interesting in the article, aside from the denigration of people wanting to understand recent trends, was an assertion by Monash University’s Amanda Lynch (climate scientist and former faculty colleague from here at Colorado) who stated that it might be 40 years (!) of no warming/cooling before observations would be inconsistent with predictions:
Most scientists are adamant that any assessment of climate change based on only 10 years of data is not only meaningless but reckless.
“From a climate standpoint it is far too short a period to have any significance,” says Amanda Lynch, a climate change scientist at Melbourne’s Monash University. “What we are seeing now is consistent with our understanding of variability between decades. If we hung about for another 30 years and it kept going down, then you might start to think there is something we don’t understand. But the evidence at this point suggests this is not something we should hang around and wait for.”
Excuse me? Another 30 years? That is a record in the “consistent with” chronicles.
Meantime, I continue to applaud serious and rigorous efforts to compare observations with predictions, in real time, and efforts to interpret their significance. The best example of such an effort continues to be the solid (but apparently reckless;-) work by Lucia Liljegren.
August 19th, 2008 at 7:32 pm
What I don’t understand is: Why are we still paying for CERN?
Why not shut down all medical research?
We have a theory now (AGW) that predicts all possible outcomes–what else do we need?
August 19th, 2008 at 7:38 pm
An another question that is beginning to form….after reading about Feynman’s investigation into the Challenger Disaster, and more recently “13 things that don’t make sense”, and worrying about Russia being our only transportation to ISS (what are its capabilities as a weapons platform?), and finally what appears to be some seriously fraudulent stuff in Hansen’s shop, are we about to have a massive meltdown in government “science”?
August 19th, 2008 at 7:43 pm
That’s me. Reckless.
I can’t help wondering what the basis for Amanda’s claim that we would need a 30 year down turn to think there is something we don’t understand.
I think the previous record for sustained downturns that aren’t inconsistent with warming was Gavin who said:
“Over a twenty year period, you would be on stronger ground in arguing that a negative trend would be outside the 95% confidence limits of the expected trend (the one model run in the above ensemble suggests that would only happen ~2% of the time).” (http://www.realclimate.org/index.php/archives/2008/05/what-the-ipcc-models-really-say/ )
His basis for saying 8 year downtrends are consistent with models is based on the variability of 8 year trends in the collection of models. That variability exceeds the variability of actual 8 year trends in the earth’s thermometer record.
So, I think the models show too much variability in 8 year trends, and when assessing the accuracy of projections, it is more reasonable to look at real earth trends. Of course, Gavin and I will likely continue to disagree.
I’m looking at other statistical properties for the model data and comparing them to the current period. When I’m done I’ll say more.
August 19th, 2008 at 7:45 pm
Nova (on PBS) is just this very minute telling me that global warming is going to be shooting through the roof as global dimming (from sulfates and ash) goes away.
The famous “double whammy” as Peter Cox just called it.
Temperatures could rise by an *extra* 2-3 degrees Celsius by mid-century, I think they just said. (I went to heat my pizza, to get in a decent final meal before I die.)
August 19th, 2008 at 7:47 pm
And James Hansen is telling me what it would be like if the sea level rose by 25 meters. (Yes, that’s 25 meters, with an “m”.)
August 19th, 2008 at 8:41 pm
Roger,
From my understanding the pivotal moment in the AGW debate came when James Hansen presented his testimony to the US senate in 1988.
As best I can tell the temperature trend that triggered this testimony started about 1977/8. Therefore he only had a ten year trend to base it on.
Admittedly the trend was much steeper but how does that Ten year trend differ in significance from this latest ten year trend?
As well the upward trend peaked in 1998 so a total trend of 20 years proves global warming but you need a negative trend of 40 years to disprove it.
August 20th, 2008 at 6:04 am
Roger: “Excuse me? Another 30 years? That is a record in the “consistent with” chronicles.”
In addition to commenting on Amanda Lynch’s apparent “record”, do you care to venture either your own opinion on how soon AGW will be “disproven”, or your basis for implying that Lynch’s suggestion is way too long? Is Gavin Schmidt, at 20 years, simply more credible?
How about running a poll?!
By the way, has anyone told the Arctic that the world has been cooling since 1998?
http://climaticidechronicles.org/2008/08/11/temperatures-hit-80-degrees-in-the-arctic-2008-may-see-a-record-sea-ice-melt-after-all/
http://nsidc.org/news/press/20080610_Slater.html
Does anyone really believe that somehow all climate noise (and natural cycles) has disappeared, so that a period of relative stasis in the global average means that man is NOT affecting a climate that is still very obviously changing?
August 20th, 2008 at 6:54 am
Tom-
I am not sure what you mean by the notion of AGW being “disproven”. The theoretical and empirical bases behind the notion that humans influence the climate system is fairly robust in my (inexpert) opinion.
However, just because we have a robust set of understandings does not mean that we can offer accurate predictions of the evolution of that system. Economics provides a good example of a similar situation. We can observe that economic forecasts are sometimes less than accurate without “disproving” economic theory.
This is where I think many people critical of Lucia Liljegren’s efforts (and to some extent my “consistent with” discussions”) confuse the evaluation of predictions with some effort to “disprove” AGW. As I’ve said before (and I think Lucia has said the same thing as well), the evaluation of long-term predictions can be done with relatively short records, however your confidence in the results might not be very high. Lucia’s discussion is valuable because she explores and presents a range of ways to evaluate this confidence. It is not a yes or no question, which is why I highlight statements by Lynch that we have to wait 40 years or Schmidt (20 years) to evaluate climate forecasts. We don’t.
August 20th, 2008 at 7:26 am
Also, Tom, it would be a good idea to ask climate scientists how long temperatures would have to be flat (or cooling) before it would cause concern about the accuracy of predictions (such as the central prediction of the IPCC). We’ve done something like this before, and it is clear that — unlike weather forecasters — many climate scientists are not really up to speed on forecast verification, so we get comments like “it takes 20 years of observations to evaluate a 30-year forecast”.
August 20th, 2008 at 10:23 pm
Roger, thanks for your responses.
While I agree with you that “many people critical of Lucia Liljegren’s efforts (and to some extent my “consistent with” discussions”) confuse the evaluation of predictions with some effort to “disprove” AGW,” I’d say that this is also much in evidence among those who applaud Lucia’s efforts – viz., they confuse the evaluation of predictions as somehow showing that AGW has been disproved or that very obvious climate change isn’t occurring.
Do you have any suggestions on any layman-accessible readings that explain more about why “the evaluation of long-term predictions can be done with relatively short records, however your confidence in the results might not be very high”?
Further, isn’t the confidence in results/meaningfulness of the evaulation precisely the question? Should an evaluation period cover at least a full ENSO cycle? Why mock Lynch and Schmidt without explaining why they are wrong?
August 21st, 2008 at 3:02 am
Actually, everything is so uncertain and the range of estimations is so wide that we have no base for reliable projections and all we can do is to monitore current climate.
50-100 yr projections are already abandoned, and shorter periods show primarily natural variations, oscillations and cycles of which the longer ones are not included in models, yet.
When this is a policy forum, I again emphasize that current actions to combat global warming are based on precaution.
I have nothing against precaution, but I call it precaution and not a proven scientific truth.
August 21st, 2008 at 6:17 am
If it takes far 40 years to properly evaluate a climate influence, then a period of warmth from 1975 until now is still too short a period to say that man is influencing climate. Indeed it invalidates many papers on climate science, which have been, and continue to be, based on 10 to 15 year periods of data.
I strongly suspect that Gavin’s 20 years and Rahmsdorf’s 18 years comes from taking that contradiction into consideration; ie the period 1980 to 1998 is the only period that can be demonstrated to be a rapid warmth apparently not attributable to natural variation. So under 15 years is too short due to 10 years of plateauing temperatures and over 20 years is too long because that would rule out the unusual late 20th century warmth theory.
But the non-warming global temperature is actually only one of several indicators that the basic theory is wrong; probably partly due to the pessimistic decision not to include negative feedbacks and partly due to the simplistic conflation of electric control theory to a chaotic, non-linear climate. Though most explanations for this theory failure tend to conclude that the obs are wrong, ie always too cool, because they disagree with the models. This is the only area of physical science where it is argued that the obs are misleading and that we should trust the models. Of course it makes no sense at all because the whole idea of a model is to try to simulate reality and obs are our only indicator of reality and errors should be evenly distributed.
TT attempts to mix the Arctic warming with global warming but not only do we have valid, competing and yet unchallenged theories about Arctic warming, eg winds, soot, solar but we also have temperature records which say that it was just as warm there in the 30’s. The main oddity of the global warming chart seems to stem from a combination of apparently unreliable sea temperature data and a peculiar spike in Siberian temperatures which overlay an apparently unnatural climate shift from 1980 to 1998 onto an otherwise natural pattern. Time will tell but in the meantime can we stop this unscientific obsession with altering obs to match what is expected from the models?
August 21st, 2008 at 11:51 am
Tom–
You seem to believe my showing +2c/century falls outside the 95% confidence intervals causes people to believe AGW is disproven. I don’t get that impression in conversation with my readers. If you think someone has developed that impression, correct them and refer them to me. I’ll explain that the tests I do not disprove AGW.
I have never encountered anyone who is unable to grasp the distinction between showing that 2 C/century lies outside the uncertainty of the data, but 0C/century lies inside it. I suspect if you explained it that way, you would have no difficulty getting them to grasp the notion either.
As for Roger’s statement that with short times, our uncertainty is large: That’s reflected in my uncertainty intervals. The 95% uncertainty intervals are currently about ±2C/century to ±3C/century depending on data set or method of estimating these intervals. That’s a large uncertainty interval. As we accumulate data, the uncertainty intervals will drop. Everyone agrees on this.
But there is no magic time when uncertainty intervals go from infinity to zero. And, if, hypothetically, a trend is sufficiently different from a prediction, we can say the prediction is incorrect– even with small amounts of data.
August 21st, 2008 at 1:18 pm
Lucia,
FYI Gary D. Sharp once stated that we need reliable data of three 70-cycles i.e. 210 yr data to draw any conclusions. We have at least 300 yrs data about 70-yr cycles but the problem is how reliable they are. Perhaps we’ll have reliable projections in 50-100 yrs.
August 21st, 2008 at 3:24 pm
Timo:
Empirically, we do need 3 cycles of length “T” anything to estimate the energy spectral density associated with cycles of period “T”.
If the modelers saying we need “N” years would suggest that we need that number because there is a disproporionate amount of energy in some particular long cycle, then
a) the consumer of climate information would have been given a basis for the recommendation and
b) people from many, many fields could use that information to estimate the amount of uncertainty associated with using fewer years.
However, the sound bites in newspaper articles are utterly vague. If someone says one can’t test any hypothesis whatsoever at all using 10 years of data, but it becomes magically testable after 30 years, that is just nuts.
Our ability to distinguish between different hypotheses improves as we obtain more data. But certainly, most must recognize that empirical tests can be used to exclude, say 10C/century, or -10 c/century based on 90 months of data.
The question is: Can we exclude 2C/century? I say yes. Others say no. But simply saying the time is too short without discussing the properties of the data is foolish. It’s sad to read scientists resorting to puffery like claiming it’s reckless to examine claims with 7 years of data and then provide no solid criteria for how one determines the correct amount of time to test data.
August 22nd, 2008 at 2:05 am
Lucia,
the shorter the data the harder it’s distinguish trend from noise.
The innumerable skyrocket projections from the short warming 1978-1998 are warning examples and prove nothing.
About human influence Akasofu has interesting considerations:
“A roughly linear global temperature increase of about 0.5°C/100 years (~1°F/100 years) seems to have occurred from about 1800, or even much earlier, to the present…This trend (0.5°C/100 years) should be subtracted from the temperature data during the last 100 years when estimating the manmade contribution to the present global warming trend. Thus, there is a possibility that only a fraction of the present warming trend is attributable to the greenhouse effect resulting from human activities…”
Ref: Akasofu, Syun-Ichi, 2008. Is the Earth still recovering from the “Little Ice Age”? A possible cause of global warming. Study, revised January 23, 2008, online http://people.iarc.uaf.edu/~sakasofu/pdf/Earth_recovering_from_LIA_R.pdf
After all these longer natural variations, oscillations and cycles which are not in models, yet, we have the shortage of reliable data and in the end, the extremely vague ‘climate sensitivity’, when we try to estimate future climates and exclude impossibilities.
Statistics is used to prove something, but too ofter it is “lie, damned lie, statistics”.