Does the IPCC’s Main Conclusion Need to be Revisited?

Här kommer flera mycket intressanta artiklar och kommentarer om en artikel i Nature 453, 646-649 (29 May 2008 ) ”A large discontinuity in the mid-twentieth century in observed global-mean surface temperature” av David W. J. Thompson1, John J. Kennedy2, John M. Wallace3 & Phil D. Jones4.

Vad det hela handlar om är hur man mätte temperaturen på 1940 talet och hur det hela påverkar IPCC:s klimatmodeller. Och att nu har Global Warminhg Hysterikerna ”upptäckt” det hela för att försöka förklara bort ”dippen” i temperaturen.  Dvs. att enligt dessa ”nya” rön (bl.a. Steve McIntyre påpekade detta redan för 3 år sedan) så blir det globala ökningen av temperaturen INTE ALLS så stor som IPCC säger i sina modeller.

Abstract:

”Data sets used to monitor the Earth’s climate indicate that the surface of the Earth warmed from approx 1910 to 1940, cooled slightly from approx 1940 to 1970, and then warmed markedly from approx 1970 onward. The weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors, such as atmosphere-ocean interactions and anthropogenic emissions of sulphate aerosols. Here we call attention to a previously overlooked discontinuity in the record at 1945, which is a prominent feature of the cooling trend in the mid-twentieth century. The discontinuity is evident in published versions of the global-mean temperature time series, but stands out more clearly after the data are filtered for the effects of internal climate variability. We argue that the abrupt temperature drop of approx 0.3 °C in 1945 is the apparent result of uncorrected instrumental biases in the sea surface temperature record. Corrections for the discontinuity are expected to alter the character of mid-twentieth century temperature variability but not estimates of the century-long trend in global-mean temperatures.”

Som Jennifer Marohasy sager:

”Amusement number one is the fact that AGW supporters have tried to explain the 1940s to 1970s ‘cooling’ using emissions of sulphate aerosols as an excuse – an explanation that I have previously challenged

Amusement number two is the unverifiable data used by Phil Jones et al 1990, which was relied upon by the IPCC to diminish the effect of urbanisation on the surface temperature record.

Amusement number three is that Steve McIntyre of Climate Audit first noted the discontinuity in the sea surface temperature record in June 2005.”

Artikel finns här:

http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/

001445does_the_ipccs_main.html

Och här:

http://www.climateaudit.org/?p=3116

http://www.climateaudit.org/?p=3114

 Och här:

http://www.jennifermarohasy.com/blog/archives/003121.html

Artikeln i Nature finns här:

http://www.nature.com/nature/journal/v453/n7195/full/nature06982.html

May 29, 2008

Does the IPCC’s Main Conclusion Need to be Revisited?

Posted to Author: Pielke Jr., R. | Climate Change | Science + Politics | Scientific Assessments

Yesterday Nature published a paper by Thompson et al. which argues that a change in the observational techniques for taking the temperatures of the oceans led to a cold bias in temperatures beginning in the 1940s. The need for the adjustment raises an interesting, and certainly sensitive, question related to the sociology and politics of science: Does the IPCC’s main conclusion need to be revisited?

The Nature paper states of the effects of the bias on temperature measurements:

The adjustments immediately after 1945 are expected to be as large as those made to the pre-war data (.0.3 C; Fig. 4), and smaller adjustments are likely to be required in SSTs through at least the mid-1960s.

Thompson et al. do not provide a time series estimate on the effects of the bias on the global temperature record, but Steve McIntyre, who is building an impressive track record of analyses outside the peer-review system, discussed this topic on his weblog long before the paper appeared in Nature, and has proposed an adjustment to the temperature record (based on discussions with participants on his blog). Steve’s adjustment is based on assuming:

that 75% of all measurements from 1942-1945 were done by engine inlets, falling back to business as usual 10% in 1946 where it remained until 1970 when we have a measurement point – 90% of measurements in 1970 were still being made by buckets as indicated by the information in Kent et al 2007- and that the 90% phased down to 0 in 2000 linearly.

The effects of McIntyre’s proposed adjustments (on the UKMET global temperature record) are shown in the following figure.

Other adjustments are certainly plausible, and will certainly be proposed and debated in the literature and on blogs (McIntyre discusses possible implications of the adjustments in this post.). But given how much research has been based on the existing global temperature record, it seems likely that many studies will be revisited in light of the Nature paper. In a comment in Nature that accompanies Thompson et al., Forest and Reynolds suggest:

The SST adjustment around 1945 is likely to have far-reaching implications for modelling in this period.

In the figure above, the trend in the unadjusted data (1950-present) is 0.11 Deg C per decade (slightly lower than reported by IPCC AR4, due to the recent downturn), and after the adjustments are applied the trend drops by just about half, to 0.06 Deg C per decade.

And this brings us to the IPCC. In 2007 the IPCC (PDF) concluded that:

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations

I interpret ”mid-20th century” to be 1950, and ”most” to be >50%. This means that the 2007 IPCC attributed more than 0.06 Deg per decade of the temperature increase since 1950 to increasing greenhouse gases. But we know now that the trend since 1950 included a spurious factor due to observational discontinuities, which reduces the entire trend to 0.06. So logically, if the proposed adjustment is in the ballpark, it would mean that one of the following statements must be true in order for the IPCC statement to still hold:

A. The entire trend of 0.06 per decade since 1950 should now be attributed to greenhouse gases (the balance of 0.06 per decade)

B. Only >0.03 per decade can be attributed to greenhouse gases (the ”most” from the original statement)

C. The proposed adjustment is wildly off (I’d welcome other suggestions for an adjustment)

D. The IPCC statement needs to be fundamentally recast

So which is it?

PS. To ensure that this blog post is not misinterpreted, note that none of the mitigation or adaptation policies that I have advocated are called into question based on the answer that one gives to the question posed in the title.

Posted on May 29, 2008 08:10 AM

Läs även andra bloggares åsikter om <a href=”http://bloggar.se/om/milj%F6“ rel=”tag”>miljö</a>

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Lost at Sea

By Steve McIntyre

Thompson et al 2008, writing in Nature, assure their readers,

the data before ~1940 and after the mid-1960s are not expected to require further corrections for changes from uninsulated bucket to engine room intake measurements

Is there a shred of evidence to support this assertion? There is convincing evidence otherwise – evidence already reported here. While Thompson et al do confirm some Climate Audit observations, on essential points, their analysis is actually a step backwards from my 2007 posts.

The hypothesis of the original Hadley Center Windowed Marine De-trending program was that there was an approximate 0.3 deg C inhomogeneity between engine inlet SST measurements and canvas bucket measurements and that there was a drop-dead changeover on December 1941, a switch which continued in place to the present day. In earlier posts, I showed that there was strong documentary evidence against this assumption and hypothesized that there was a return to ”business as usual” after the war. That’s not the only relevant information on the transition, as I’ll show below.

Thompson et al 2008 agree that there was a return to ”business as usual” after the war, citing related but somewhat different evidence than presented here: they observed that wartime measurements were predominantly U.S., which they say were engine inlet, while U.K. measurements come back into play after the war, using a ~0.3 deg C estimate. They observe:

The Met Office Hadley Centre is currently assessing the adjustments required to compensate for the step in 1945 and subsequent changes in the SST observing network. The adjustments immediately after 1945 are expected to be as large as those made to the pre-war data (~0.3 deg C; Fig. 4).

This was also the conclusion in the prior Climate Audit post and is fair enough as a first estimate. They go on to say:

smaller adjustments are likely to be required in SSTs through at least the mid-1960s, by which time the observing fleet was relatively diverse and less susceptible to changes in the data supply from a single country of origin …

the data before ~1940 and after the mid-1960s are not expected to require further corrections for changes from uninsulated bucket to engine room intake measurements.

They’ve worded their comment on the early bucket adjustments carefully, as there’s lots of hair on these early adjustments and these adjustments need to be minutely scrutinized. But on the post-1960s period, they have completely lost their bearings and are, so to speak, lost at sea.

Thompson et al 2008 cited Kent et al 2007, an important discussion of metadata, but they completely failed to discuss or cite the most relevant graphic in Kent et al – a graphic previously reproduced at Climate Audit on a number of occasions – and reproduced one more time below. This graphic, based on a very comprehensive examination of metadata, showed the distribution of measurement type from 1970 to 2006.

In 1970, as I observed last year, about 90% (this is a visual estimate from the graphic) of SST measurements, for which the type is known, were done by buckets. Because the proportion with metadata is a very large sample, it’s plausible to use this 90% estimate for the entire population, including the unknown population.

Between 1970 and 2006, the proportion of bucket and engine inlet measurements is more or less reversed, with about 90% of SST measurements in the 2000s being engine inlet or hull sensor, the latter by the way, being a further addition to the witches’ brew that the Nature boys didn’t mention at all. The starting point of all this was that there is about a ~0.3 deg C bias between engine inlet and buckets.

However, Thompson et al 2008 completely failed to grasp the significance of this graphic. The changeover to engine inlet measurements, previously attributed to a drop-dead date in 1941, actually took place AFTER 1970 (providing, of course, for a one-off WW2 adjustment ending in 1945). If the same ~0.3 deg C consistently used by Hadley Center is applied after 1970, as this information shows, this comes off the post-1970 SST trend (and has to be allocated much earlier, as proposed last year at Climate Audit, ) refuting the claims of Thompson et al that no substantial changes are required to the post-1965 record, a point that should be obvious to anyone thinking for 5 minutes about the problem.

Thompson et al 2008 observe that the 0.3 deg adjustment looms relatively large in 20th century terms. They observe:

thus the amplitude of the drop is roughly 40% as large as the 0.75 deg C rise in [global temperature] from 1900 to 2006,

If, as outlined here, this 0.3 deg C adjustment has to come off the post-1970 record, as implied by the information at hand, it is a very large proportion of the post-1970 temperature increase, which is much reduced and allocated earlier in the century. Because the effect is so large relative to observed changes, the knock-on impact for attribution and modeling will not be small – whatever way it goes.

One hopes that this will also lead to an end to CRU secrecy on their source code, algorithms and data versions.

References:

Folland, C. K., D. E. Parker, and F. E. Kates. 1984. Worldwide marine temperature fluctuations 1856-1981. Nature 310, no. 5979: 670-673.

Kent, E. C., S. D. Woodruff, and D. I. Berry. 2007. Metadata from WMO Publication No. 47 and an Assessment of Voluntary Observing Ship Observation Heights in ICOADS. Journal of Atmospheric and Oceanic Technology 24, no. 2: 214-234.

Parker, D. E., C. K. Folland, and M. Jackson. 1995. Marine surface temperature: Observed variations and data requirements. Climatic Change 31, no. 2: 559-600.

Etiketter: IPCC, Klimatmodeller, Temperaturdata