A guest post by Basil Copeland
Lucia, at rankexploits.com, has been musing over Tilo Reber’s posting of a graph showing flat 11 year trends in the HadCRUT land-ocean global temperature anomaly and the two MSU satellite data sets, UAH and RSS. In answer to the question whether global warming is on an 11 year hiatus, “not quite,” says Lucia. She challenges Tilo’s omission of the GISS data set, because notwithstanding questions about the reliability of GISS, it still shows a positive trend over the 11 year period in question. Unless all the measures show a flat trend, Lucia’s not ready to conclude that global warming has been on an 11 year hiatus.
I understand the desire to look at as many metrics as possible in trying to divine what is going on with globally averaged temperature. I also understand the reasons for questioning the reliability of GISS. What I don’t understand is why the only measure of trend that seems to count is a trend derived from linear regression. William Briggs recently had an interesting post to his blog on the relationship between trends in CO2 and temperature in which he introduced the use of loess lines to track trends that are not represented well by linear regression. Loess refers to a type of locally weighted regression that in effect fits a piecewise linear or quadratic trend through the data, showing how the trend is changing over time. Especially in an environment where the charge of cherry-picking the data — choosing starting and ending points to produce a particular result – is routinely made, loess lines are a relatively robust alternative to simple trend lines from linear regression.
Click for a larger image
Figure 1 fits a loess line through the data for GISS using the same 11 year period used by Tilo Reber (except that I’ve normalized all anomalies in this discussion relative to their 11 year mean to facilitate comparison to a common baseline). The red line is the GISS anomaly for this period, about its mean, and the blue line is the loess line. While it varies up and down over the period in question, I would argue that the overall trend is essentially flat, or even slightly negative: the value of line at the end of the period is slightly lower than at the beginning of the period. What this loess line shows is that a linear regression trend is not a particularly good way to represent the actual trend in the data. Without actually fitting a linear trend line, we can reasonably guess that it will trend upwards, because of the way the loess line is lower in the first half of the period in question, and higher in the second half. Linear regression will fit a positive, but misleading, slope through the data, implying that at the end of the period the GISS is on an upward trend when in fact the trend peaked around 2006 and has since declined.
Click for a larger image
Figure 2 is rainbow of colors comparing all four of the metrics we tend to follow here on WUWT. Not surprisingly, the loess lines of HadCRUT, UAH and RSS all track closely together, while GISS is the odd duck of the lot. So what does this kaleidoscope of colors tell us about whether global warming is has gone on an 11 year hiatus? I think it tells us rather more than even Tilo was claiming. All of the loess lines show a net decline in the trend over the 11 year period in question. It is relatively minor in the case of GISS, but rather pronounced in the case of the other three. Of the other three, the median anomaly at the beginning of the period, as represented by the loess lines, was 0.125; at the end of the period, the median anomaly had dropped to -0.071, for a total decline of 0.196, or almost 0.2C.
Global warming on hiatus? It looks to me like more evidence of global cooling. Will it continue? Neither linear regression nor loess lines can answer that question. But the loess lines certainly warn us to be cautious in naively extrapolating historical trends derived by simple linear regression.
Not even GISS can support the conclusion from the last 11 years of data that global warming continues to march upward in unrelenting fashion.
Zeke–
Fair enough.
I read the bit you quoted as referring to the climate trend, as it’s my policy to read casual blog comment in a way that makes them correct if at all possible. (Mostly because I know I dash off blog comments quickly, and I figure everyone else does too!)
The link to RC threw me, as, it seems to me, Gavin sets out to rebut some idea that that the IPCC claimed weather itself will increase monotonically. The individual scenarios are like “weather”, but I don’t think the IPCC is ever understood by anyone to project any individual weather trajectory.
Still, I do see how someone might intepret the person you quoted as thinking the IPCC predicts monotonic weather. The IPCC doesn’t do that, partly because they don’t predict weather. (Partly because weather can’t do that.)
I like long-term trend lines, they speak volumes:
Hadley CRUT temperatures plotted against CO2 levels. Note how the two trend lines start to diverge in the 1980’s – temperature is less and less correlated to CO2 levels, which is to be expected. This is because additional CO2 introduced to the atmosphere has less and less warming effect:
http://i32.tinypic.com/28h3dqh.jpg
Likewise, CO2 has an anticipated modest warming effect and has tracked consistently with actual temperatures except during the warmer 1990’s. But the IPCC projected climate sensitivity to CO2 predicts temperature trends rising exponentially any time now:
http://i27.tinypic.com/25fuk8w.jpg
Unless it can be shown the oceans are absorbing ever more heat – and evidently the Argo data show far lower heat content than expected (as per Kevin Trenberth of NCAR) – the AGWers don’t have a case for dangerous AGW. Less than ideal, perhaps. Dangerous, that remains to be seen.
The higher latitudes are far more responsive to changes. The greatest damage to Greenland’s ice has been caused by snow-warming heat absorbent soot, the effect is greatest at the peripheral glaciers where the sooty runoff accumulates and compounds the effect. Arctic sea ice has suffered from sootfall similarly and wind dynamics have been causing a great deal of recent ice thinning. So the Arctic soot situation – which constitutes something like 20 percent of all warming since the mid 19th century – can be ameliorated.
The Antarctic is not under any grave threat of melt-off, it has been shown to be much drier than modeled (like the ice ages) and less prone to warming.
The same goes for the Earth’s middle troposphere, also drier than expected by the AGW climat models.
This is the problem with using linear regression on a time series:
http://hallofrecord.blogspot.com/2008/05/telling-tall-tales-with-trends.html
Regardless, there are a number of approaches to a “best fit” line that will give you significantly different end points. For example, on the graph of local temperatures this winter/spring, I used a polynomial 3rd order expression and it shows a slightly declining trend at the end. The same data with a 4th order results in a somewhat different line.
http://hallofrecord.blogspot.com/2008/06/cold-start-to-2008.html
Part of the problem is that the data itself is longer term oscillating more than trending and 10 years may be just the beginning of the down leg of an oscillation.
Hadley CRUT temperatures plotted against CO2 levels:
Note how the two trend lines start to diverge in the 1980’s – temperature is less and less correlated to CO2 levels, which is to be expected. This is because additional CO2 introduced to the atmosphere has less and less warming effect:
(http://i32.tinypic.com/28h3dqh.jpg)
Likewise, CO2 has an anticipated modest warming effect and has tracked consistently with actual temperatures except during the warmer 1990’s. But the IPCC projected climate sensitivity to CO2 predicts temperature trends rising exponentially any time now:
(http://i27.tinypic.com/25fuk8w.jpg)
The oft-cited paleo record may not be as conclusive as it first appears. There are instances where water vapor unlocked during interglacial periods rises and falls in a pattern unrelated to CO2 levels. Both water vapor and CO2 levels lag temperature increases, and other interesting dyssynchronies appear in the paleo data: (http://i30.tinypic.com/izon5h.jpg)
[…] individual bloggers have expressed a strong preference for one particular data set or another. Like Atmoz, I prefer not […]
Basil,
The Hodrick-Prescott analysis just smokes! It is so much more revealing than the loess. Major kudos for your discoveries! When is the paper to be published?
Now all the algorian prius driving knee sock and sandals carbon footprint crowd can say “see working together we can overcome global warming, just look at the temperatures since we, the new patriots, took control of mother nature!” Its the next play from the liberal play book! By the way, check out what the libs are doing for the DNC in Denver. WOA!!! More planet saving ahead for us thank gore!
Amid the universal clamour for maximum sample periods, may I ask for an inclusion of unadjusted surface data in the mix? I understand this is a problem for the software with lacunae and all, but otherwise I see no accomodation for my plurality of concern: The absence of justification for ‘enlightened’ data modification. I feel ignored, “Reason not the need!”
REPLY: The only “unadjusted” surface data in existence in on the B91 forms stored in the basement of NCDC and online as PDF files. Yeah, I’ll get right on that.
Ooops, wrong thread. My sincere apology.
[…] Has Global Warming Become Religion? July 2, 2008 Posted by tkcollier in Enviroment, Religion, Science & Technology. Tags: Global Cooling, Global Warming trackback Global View – WSJ.com But mother nature has opinions of her own. NASA now begrudgingly confirms that the hottest year on record in the continental 48 was not 1998, as previously believed, but 1934, and that six of the 10 hottest years since 1880 antedate 1954. Data from 3,000 scientific robots in the world’s oceans show there has been slight cooling in the past five years, never mind that “80% to 90% of global warming involves heating up ocean waters,” according to a report by NPR’s Richard Harris. A discussion of the various measurement models. […]
The danger to the planet is an optical illusion. The cost/benefit of controlling CO2 is just not worth it. There are serious heating issues with heating in the cities, but this is urban. Many more lives are lost from winter weather, and urban heating actually saves lives. There is serious trouble in HIV/Aids, drinkable water, and wasting energy, but critical thinking is required to solve the world’s issues. CO2 is de minimis. Prosperity, however, is being seriously threatened by NGO lobby groups with tunnel vision. Go to the Copenhagen Convention web site to get an update about what needs to be done. It is not heavy industry at fault. It is politically correct politicians fishing for politically correct constituencies using politically correct red herring for bait.
Eric Hoffer, 1951 – “The True Believer – Thoughts on the Nature of Mass Movements”
P.11
“When hopes and dreams are loose in the streets, it is well for the timid to lock doors , shutter windows and lie low until the wrath has passed. For there is often a monstrous incongruity between the hopes, however noble and tender, and the actions that follows them. It is as if ivied maidens and garlanded youths were to herald the four horsemen of the apocalypse.
And p.12
“People who see their lives as irremediably spoiled cannot find a worth-while purpose in self-advancement…Their innermost craving is for a new life – a rebirth – or failing this, a chance to acquire new elements of pride, confidence, hope, a sense of purpose and worth by an identification with a holy cause. An active mass movement offers them opportunities for both…”
and P. 13
“ It is true that in the early adherents of a mass movement there are also adventurers who join in the hope that that the movement will give a spin to their wheel of fortune and whirl them to fame and power.”
And
Eric Hoffer, 1979 – “Before the Sabbath”
p. 7
“ I am curious about Pechorin, a Russian intellectual of the mid-nineteenth century who wrote a poem on “How sweet it is to hate one’s native land and eagerly await its annihilation.”