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Monday, 1 May 2017

Historical temperature records






The first comment on Willis Eschenbach's blog piece about me that I am going to mention is this one, primarily because it was also posted as a comment directly on my this blog. 

"Do you really believe that Russian temperature records from, say, 1917-1950 are reliable?

You don't really expect a rational person to believe that people were making accurate daily observations all over Russia during the Revolution or during the Sieges of Stalingrad and Leningrad?

Do you honestly believe that Chinese temperature records from, say, 1913-1980 are reliable?

Do you really expect anybody to believe that accurate daily temperatures were recorded in China during the Revolution or "The Great Leap Forward?"

Do you seriously believe that Sub-Saharan African temperatures from, say 1850-1975 are accurate?

Please don't tell us you think accurate daily temperature recordings were made in Sub-Saharan Africa during any part of the 19th century and most of the 20th.

Do you really believe that oceanic temperatures from, say 1800-1970 are accurate? ( as we know, the oceans cover 70% of the earth’s surface).

Do you really believe there were accurate daily temperature observations made in the Bering Sea or the Weddell Sea or in the middle of the Pacific at any time before the advent of satellite observations in 1979?

Are you kidding?

All this is even prior to considering the GISS homogenization adjustments or the adjustments made for the UHI effect.

These are measurement error and uncertainties in excess of the putative change in global temperatures."

I will deal with the two parts of this separately, the first part dealing with historical temperature records. This is best answered by Carol Rasmussen's article on the NASA website from 20th July 2016, entitled "Historical records miss a fifth of global warming".

Rasmussen points to a NASA study from 2016 (not open access but there is a summary) which reports that almost a fifth of global warming over the past 150 tears has been missed by historical records due to quirks in how the temperatures were recorded. These quirks hide around 19 percent of global air warming since the 1860s. This means that calculations generated from historical records alone were cooler than about 90 percent of the results from the climate models that the IPCC uses for its assessment reports. So, in essence, yes there is a problem with the reliability of historical records, but it seems that the quirks actually underplay the amount of warming since 1860 rather than exaggerating it. So if the anonymous poster of this comment is expecting the unreliability of the historical records to show a cooler planet, rather than the warming planet, he/she is in for a disappointment...well, assuming he/she would take notice of it anyway, which is probably unlikely. 

Secondly, we come to the point about homogenisation adjustments, particularly GISS and the Urban Heat Island (UHI) effect. 

There is a useful Frequently Asked Questions (FAQ) about this on the NASA site.

What is GISTEMP?
The GISTEMP analysis recalculates consistent temperature anomaly series from 1880 to the present for a regularly spaced array of virtual stations covering the whole globe. Those data are used to investigate regional and global patterns and trends.  

Why use adjusted data rather than raw data?
GISS uses temperature data for long-term climate studies. For station data to be useful for such studies, it is essential that the time series of observations are consistent, and that any non-climatic temperature jumps, introduced by station moves or equipment updates, are corrected for. In adjusted data the effect of such non-climatic influences is eliminated whenever possible. Originally, only documented cases were adjusted, however the current procedure used by NOAA/NCEI applies an automated system that uses systematic comparisons with neighboring stations to deal with undocumented instances of artificial changes. The processes and evaluation of these procedures are described in numerous publications — for instance, Menne et al., 2010 and Venema et al., 2012 — and at the NOAA/NCEI website.

Does GISS do any data checking and alterations?
Yes. GISS applies semi-automatic quality control routines listing records that look unrealistic. After manual inspection, those data are either kept or rejected. GISS does make an adjustment to deal with potential artifacts associated with urban heat islands, whereby the long-term regional trend derived from rural stations is used instead of the trends from urban centers in the analysis. 

Does NASA/GISS skew the global temperature trends to better match climate models?
No.

How did the GISS analysis and their sources change over time, and how did this affect the results?
The procedure used in the mid 1980s has not been changed significantly, except for the addition of an urban adjustment scheme. However, more station data became available; also, ocean data became available whose anomalies were used to estimate surface air temperature anomalies over the oceans. More information is presented in the History Section and two of these changes are discussed in more detail in the next two questions. The changes in the results stayed within the margin of error indicated in a prior Q&A.   

Judith Curry has also written about adjustments to temperature data here.

"The large contribution of adjustments to century-scale U.S. temperature trends lends itself to an unfortunate narrative that 'government bureaucrats are cooking the books'", she says. "Having worked with many of the scientists in question, I can say with certainty that there is no grand conspiracy to artificially warm the earth; rather, scientists are doing their best to interpret large datasets with numerous biases such as station moves, instrument changes, time of observation changes, urban heat island biases, and other so-called inhomogenities that have occurred over the last 150 years. Their methods may not be perfect, and are certainly not immune from critical analysis, but that critical analysis should start out from a position of assuming good faith and with an understanding of what exactly has been done."

"The problem is that (with the exception of the newly created Climate Reference Network), there is really no such thing as a pure and unadulterated temperature record. Temperature stations in the U.S. are mainly operated by volunteer observers [called the Cooperative Observer Network]". 

"Many of these stations were set up in the late 1800s and early 1900s as part of a national network of weather stations, focused on measuring day-to-day changes in the weather rather than decadal-scale changes in the climate."


"Nearly every single station in the network in the network has been moved at least once over the last century, with many having 3 or more distinct moves. Most of the stations have changed from using liquid in glass thermometers (LiG) in Stevenson screens to electronic Minimum Maximum Temperature Systems (MMTS) or Automated Surface Observing Systems (ASOS). Observation times have shifted from afternoon to morning at most stations since 1960, as part of an effort by the National Weather Service to improve precipitation measurements.

All of these changes introduce (non-random) systemic biases into the network. For example, MMTS sensors tend to read maximum daily temperatures about 0.5 C colder than LiG thermometers at the same location. There is a very obvious cooling bias in the record associated with the conversion of most co-op stations from LiG to MMTS in the 1980s, and even folks deeply skeptical of the temperature network like Anthony Watts and his coauthors add an explicit correction for this in their paper.

Time of observation changes from afternoon to morning also can add a cooling bias of up to 0.5 C, affecting maximum and minimum temperatures similarly. 

Because the biases are large and systemic, ignoring them is not a viable option. If some corrections to the data are necessary, there is a need for systems to make these corrections in a way that does not introduce more bias than they remove."

Curry's piece then goes on to discuss the types of adjustments carried out and who/which institutes or organisations actually carry them out.

The result of all this is that the values resulting from the temperature adjustments change by only small amounts on a daily basis.

Finally, there is Skeptical Science (SkS). This website is routinely and regularly criticised by deniers on the basis of some aspects of the lifestyle and interests of its founder (completely irrelevant to the material it presents), and also, like me, it doesn't 'do science' itself, but accumulates information from a phenomenally wide amount of properly peer-reviewed scientific papers and studies. Is the material on Skeptical Science trustworthy and accurate? Yes it is. Who writes this stuff? Well you can see here.

In the SkS piece on Homogenisation of Temperature Data, Kevin C (Kevin Cowtan) makes the following points:

  • The adjustments have only a modest impact on global temperature estimates
  • The claim that the adjustments increase the warming trend in the data is strange because sea surface temperatures play a larger role in determining global temperature than the weather station records, and are subject to a larger adjustments in the opposite direction. 



Kevin tested the assumptions underlying temperature homogenisation from scratch and also released all the computer code for the adjustments, here. He also produced a video of his assessment:


Kevin said that the tests he carried out on the NOAA data and code showed no sign of bias. However his conclusions can be summarised thus:
  • Are there inhomogeneities in the data? Yes
  • Can they be explained by sporadic changes in the measurement apparatus or protocols? Yes
  • Can they be detected by records from neighbouring measurement stations? Yes
  • Can they be corrected? Yes
  • Does the Global Historical Climatology Network (GHCN) method produce reasonable estimates of the size of the adjustments? Yes
Kevin Cowtan's full paper on his assessment of the adjustments can be read and downloaded here.

Another paper covering this, by Williams et al (2012), is here.

 [Kevin is an interdisciplinary computational scientist of 20 years experience, based in the UK, although he has also spent two sabbaticals at San Diego Supercomputer Center. His first degree is in theoretical physics, his doctoral thesis was primarily computational, and he now teaches chemistry undergraduates and biology post-graduates. Most of his reasearch has been focussed on data processing and analysis. He is the author or co-author of a number of highly cited scientific software packages. His climate investigations are conducted in the limited spare time available to a parent, and are currently focussed in two areas; coverage bias in the instrumental temperature record, and simple response-function climate models. He is also interested in philosophy of science and science communication.]

So in other words, the accusation that temperature adjustments are part of some big scam is completely without any foundation or truth.














 

2 comments:

  1. Sir,
    Your reply is wholly unresponsive to the main original comment. Nobody in their right mind believes historic temperature records for much of the earth and oceans prior to the advent of satellite-based observation in 1979.

    ReplyDelete
  2. Er, no its not. The NASA study from 2016 referred to above answers the question. The quirks in the historical temperature record (including the one's you refer to) actually underplay the amount of warming. You should read the answer properly.

    ReplyDelete

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