Update on Falsifiability of Climate Predictions
March 15th, 2008Posted by: Roger Pielke, Jr.
UPDATE 2:40PM 3-15-08: Within a few hours of this post, as we might have expected, rather than contributing to the substantive discussion, a climate scientist chooses instead to tell us how stupid we are for even discussing such subjects. We are told that “until the temperature obviously and unambiguously turns up again, this kind of stuff is going to continue.” Isn’t that what this post says? For the “stuff” read on below.
Regular readers will recall that not long ago I asked the climate community research community to suggest what climate observations might be observed on decadal time scales that might be inconsistent with predictions from models. While Real Climate has decided to take a pass on this question other scientists and interested observers have taken up the challenge, no doubt with interest added by the recent cooling in the primary datasets of global temperature.
A very interesting perspective is provided by Lucia Liljegren, who has several interesting posts on observations versus predictions. The figure above is from her analysis. Her complete analysis can be found here. She has several follow up posts in which she discusses other aspects of the analysis and links to a few other, similar explorations of this issue. She writes:
No matter which major temperature measuring group we examine, or which reasonable criteria for limiting our choices we select, it appears that possible that something not anticipated by the IPCC WG1 happened soon after they published their predictions for this century. That something may be the shift in the Pacific Decadal Oscillation; it may be something else. Statistics cannot tell us.
It may turn out that this something is a relatively infrequent but climatologically important, feature that results in unusually cold weather . Events that happen at a rate of 1% do happen– at a rate of 1%. So, if recent flat trend is the 1% event, then 30 year trend in temperatures will resume.
For what it’s worth: I believe AGW is real, based on physical arguments and longer term trends, I suspect we will discover that GCM’s are currently unable to predict shifts in the PDO. The result is the uncertainty intervals on IPCC projections for the short term trend were much too small.
Of course, the reason for the poor short term predictions may turn out to be something else entirely. It remains to those who make these predictions to try to identify what, if anything, resulted in this mismatch between projections and short term data. Or to stand steadfast and wait for La Nina to break and the weather to begin to warm.
Those wanting to quibble with her analysis would no doubt observe that the uncertainty around IPCC predictions for the short term is undoubtedly larger that then IPCC itself presented. Lucia in fact suggests this in her analysis, making one wonder if uncertainties are indeed larger than presented, why didn’t the IPCC say so?
In 2006 my father and I wrote about the possible effects on the climate debate of short-term predictions that do not square with observations:
predictions represent a huge gamble with public and policymaker opinion. If more-or-less steady global warming does not occur as forecast by these models, not only will professional reputations be at risk, but the need to reduce threats to the wide spectrum of serious and legitimate environmental concerns (including the human release of greenhouse gases) will be questioned by some as having been oversold. For better or worse, a failure to accurately predict the changes in the global average surface temperature, global average tropospheric temperature, ocean average heat content change, or Arctic sea ice coverage would raise questions on the reliance of global climate models for accurate prediction on multi-decadal time scales.
In one of the comments in response to that post a climate scientist (and Real Climate blogger) took us to task for raising the issue suggesting that there was no really reason to speculate about such things given that, “I’ve pointed out that in the obs, there is no sign of > 2 yr decreasing trends.”
Another climate scientist commented that climate models were completely on target:
Re the possibility that the Earth is acting in a way that the models hadn’t predicted, I must say I’m pretty relaxed about that. Let’s wait a few more years and see, eh?
I have not yet seen rebuttals to Lucia’s analysis, or others like it (she points to a few), which are not peer-reviewed analyses, yet certainly of some merit and worth considering. There continues to be good reasons for climate scientists to begin more openly discussing the limitations of short-term climate predictions and the implications for understanding uncertainties. They have these discussions among themselves all of the time. For example, with a view quite similar to my own, Real Climate’s Gavin Schimdt suggests that if the full context of a prediction from a climate model is not understood, then:
model results have an aura of exactitude that can be misleading. Reporting those results without the appropriate caveats can then provoke a backlash from those who know better, lending the whole field an aura of unreliability.
None of this discussion means that the basic conclusion that greenhouse gases affect the climate system is wrong, or that action to mitigate emissions do not make sense. What it does mean is that we should be concerned about the overselling of climate predictions and the corresponding risks to public credibility and advocacy built upon these predictions.
March 15th, 2008 at 9:58 am
The prediction techniques to project temps by ipcc etc seem woefully inadequate. Given the complexity and the uncertainty of the inputs, gradually diverging upper and lower bound lines don’t seem intuitive. It seems obvious to me that we should see accelerating divergence in possible preditions, especially on the large timeframses.
There seems to be far more certainty in the projections than there could possible exist.
March 15th, 2008 at 10:54 am
Roger says:
“What it does mean is that we should be concerned about the overselling of climate predictions and the corresponding risks to public credibility and advocacy built upon these predictions.”
We must also be concerned about UNDERselling, and the corresponding risks!
The path between Scylla and Charybdis is VERY narrow; you know, “tipping points” and “scientific reticence” and all that, are serious problems that are not faced well by ‘either side’.
March 15th, 2008 at 3:21 pm
Well, of course “until the temperature obviously and unambiguously turns up again, this kind of stuff is going to continue.”
But that’s just the point: The IPCC projections are inconsistent with downturns that last considerable lenghts of time. So, when we see relatively long, 8-10 year, periods with no “uptrend”, then people will observe this is inconsistent with IPCC projections.
As for William’s criticism that I must think the uncertainty intervals include weather noise, that’s incorrect. My analysis assumes the IPPC uncertainty intervals do NOT include weather noise. My uncertainty intervals are for the estimate of the central tendency; their uncertainty intervals are for the estimate of the central tendency. I compared like to like.
So, far from making the mistake he suggest, he confirms I interpreted those uncertainty intervals correctly. Oddly enough, if the uncertainty intervals published by the IPPC did include weahter noise, that would mean they are *even further off*!
March 16th, 2008 at 8:17 pm
“We are told that ‘until the temperature obviously and unambiguously turns up again, this kind of stuff is going to continue.’”
No “or if.” There’s an optimist.
March 16th, 2008 at 8:52 pm
Oops. That should have been:
“No ‘or unless.’ There’s an optimist.
”
March 17th, 2008 at 7:03 am
This whole accelerating uptrend assumption that are central to climate models are based on about 8 years of abnormally warm climate data, so using 8 years of data to disprove it is not unreasonable at all. The whole climate change (aka global warming) debate is based on shaky science. It is more about scaring people and politicians into making irrational decisions than it is about reality. The only proposals you see do nothing to reduce atmospheric CO@, but they do shift wealth from one person to another. Models based on considerably more assumptions than known facts do not equate to scientific proof. However, that is what the current ’scientific consensus’ is.
March 17th, 2008 at 7:15 am
If this planet has so-called tipping points, we should have 4 billion years of history consisting of violent temperature swings. Instead we seem to have naturally negative feedback mechanisms that serve to keep temperature swings in check. Of course CO2 has n’t ever been shown to drive climate change. This is the first century of data out of 4 billion years that supports this theory.
March 17th, 2008 at 11:14 am
Tamino is a statistician specializing in time series analysis. I know enough Fischer-Pearson style statistics to vouch for the quality of his work. Here are links to four of his threads discussing temperature trends:
http://tamino.wordpress.com/2007/12/16/wiggles/
http://tamino.wordpress.com/2007/08/31/garbage-is-forever/
http://tamino.wordpress.com/2008/01/09/dead-heat/
http://tamino.wordpress.com/2008/01/24/giss-ncdc-hadcru/
March 17th, 2008 at 11:36 am
JonMo states “Of course CO2 has n’t ever been shown to drive climate change.” But it has. One of the best established facts of atmospheric physics.
I recommend reading “The Discovery of Global Warming”, here:
http://www.aip.org/history/climate/index.html
March 17th, 2008 at 2:54 pm
I think we do have 4 billion years of violent climate shifts, but point still taken.
I second Dave Benson’s recommendation of Spencer Weart’s book. It is quite the laugh.
March 17th, 2008 at 4:07 pm
Hi Roger, you’re a bit ratty today. I didn’t call you stupid and I no longer call myself a climate scientist.
As for the substance, you’re ignoring it: the point that you and Lucia seem to have missed is that the projections in the IPCC graph don’t include uncertainty due to weather noise.
I can explain this to you if you don’t understand it, but I’m a bit puzzled by you not understanding it, because its fairly simple and also fairly basic. And its in my post, which you’ve at least partly read.
March 17th, 2008 at 4:08 pm
Hi Roger, you’re a bit ratty today. I didn’t call you stupid and I no longer call myself a climate scientist.
As for the substance, you’re ignoring it: the point that you and Lucia seem to have missed is that the projections in the IPCC graph don’t include uncertainty due to weather noise.
I can explain this to you if you don’t understand it, but I’m a bit puzzled by you not understanding it, because its fairly simple and also fairly basic. And its in my post, which you’ve at least partly read.
March 17th, 2008 at 4:10 pm
Oops, sorry for the repeat, your server was throwing out odd error messages: “Rebuild failed: Writing to ‘/home/html/prometheus/archives/author_pielke_jr_r/index.html.new’ failed: Opening local file ‘/home/html/prometheus/archives/author_pielke_jr_r/index.html.new’ failed: Permission denied”. Do please delete the dupl, and this.
March 17th, 2008 at 5:25 pm
Steve Bloom noticed this
http://www.skepticalscience.com/Comparing-IPCC-projections-to-observations.html
commentary on a paper in “Science” last May. The conclusion, for temperature, is that IPCC TAR was on the low side of the actual temperature trend.
March 18th, 2008 at 12:43 am
William-
Lucia is saying that recent trends are inconsistent with the IPCC prediction. You are saying that they are in fact consistent. She has showed her work. You have showed a little blog attitude and nothing more.
If you want to teach us something, then please just show the quantitative basis behind your claims that recent trends are consistent with IPCC predictions, rather than just asserting that claim without evidence. I’d guess you won’t, but if you do we’ll highlight your work here.
March 18th, 2008 at 4:34 pm
Roger Pielke, Jr. — Take the time to read Tamino’s posts that I linked above, and also the Skeptical Science link. I think you’ll find that these are reasonably consistent with the IPCC TAR predictions, which seem to be a bit on the low side.
Which occurred, I opine, because IPCC didn’t really see the rapid industrialization of India and especially China coming…
March 18th, 2008 at 11:29 pm
In climate science it is not enough to support the consensus. To not be demonize one must embrace the religion.
Just like in any other religion, one cannot doubt or even question anything from the sacred book, one must accept everything for the better or the worst. After all the bible wasn’t written by men it was written the messengers of god.
Only the real climate scientists, speaking the thruth of the AR4, have the luxury to call another scientist works heresy and do so by the sole will of his words. After all his words are his commands.
March 19th, 2008 at 2:17 pm
David Benson’s opinion that the IPCC’s TAR predictions were ‘a bit on the low side’ because the Panel ‘didn’t really see the rapid industrialization of India and especially China coming’ is mistaken on several counts.
The main one is that the IPCC scenario with the highest projections of growth in output and rapidity of industrialisation – the A1 scenario – predicted the LOWEST increase in temperatures, and vice versa: see Table II.4 in Appendix II to ‘Climate Change 2001: The Scientific Basis’.
March 19th, 2008 at 2:19 pm
David Benson’s opinion that the IPCC’s TAR predictions were ‘a bit on the low side’ because the Panel ‘didn’t really see the rapid industrialization of India and especially China coming’ is mistaken on several counts.
The main one is that the IPCC scenario with the highest projections of growth in output and rapidity of industrialisation – the A1 scenario – predicted the LOWEST increase in temperatures, and vice versa: see Table II.4 in Appendix II to ‘Climate Change 2001: The Scientific Basis’.
March 19th, 2008 at 2:39 pm
Ian Castles — Thanks for the correction.
March 20th, 2008 at 6:36 pm
David Benson, In one of your postings on 17 March you cited an article by Rahmstorf et al in ‘Science’ (4 May 2007), in which observations since 1990 of global temperature were compared with IPCC projections.
The authors of this article misunderstood the basis of the ‘projections’ for 1990-2000 in the IPCC’s Third Assessment Report (2000). As explained in the Special Report on Emissions Scenarios (2000), ‘the 1990 and 2000 emissions scenarios were standardized in all the SRES scenarios, with emissions diverging after the year 2000′ (Box 5.1, p. 243).
The SRES went on to explain that ‘The standardized scenarios share the same values for emissions in both 1990 and 2000′, and that ‘The 1990 and 2000 emissions estimates for all gases, except SO2, were set to be equal to the initial values in the unadjusted four marker scenarios.’ So, for example, the projections for emissions AND FOR TEMPERATURE for the A1FI scenario, which was not a marker, were set BY ASSUMPTION as equal to those of the average of the four markers.
As an indication of the possible scale of the effect of this procedure, the A1FI scenario assumed that the global energy supply from coal would increase by 30% between 1990 and 2000, compared with an increase of about 5% for the A1B and B1 scenarios.
.
So when Rahmstorf et al concluded that ALL OF the IPCC projections underestimated the temperature rise, they were not in fact evaluating the performance of models against observations – at least as far as the 1990-2000 period was concerned (the greater part of the comparison). For this period, the outputs of the individual models were discarded in favour of an average of a subset of the models.
Contrary to the claims in Rahmstorf et al (2007), the analysis does not in fact represent an evaluation of the IPCC models for the 1990-2000 decade. For the period 2000-2020, the IPCC models projected an increase of about 0.2 C per decade, as shown in Lucia’s graphic above.
March 21st, 2008 at 12:48 pm
For the record, I agree with Ian Castles’s interpretation.