WHEN IS A TREND NOT A TREND?

There has recently been discussion on the blogosphere as to whether or not global temperatures are continuing to rise, have levelled off, or are falling. For example the ‘Met Office in the Media’ site had a rebuttal of an article in the (United Kingdom) Daily Mail which, inter alia, claimed there had been no warming for 15 years. (http://metofficenews.wordpress.com/2012/01/29/met-office-in-the-media-29-january-2012/) In their rebuttal the Met Office pointed out that most of the highest temperatures on record have occurred in the last 15 years. They also present a chart of temperature in 10 years blocks which showed that the first decade of the 21stcentury was the warmest on record.

In the IPCC Technical Assessment Report of 2007 many of the temperature graphs are smoothed using 13 point binomial moving average (for example figure 3.8). Elsewhere they talk of decadal smoothing. One of the contributors to the blog in support of the Met Office’s position refers to the ‘Skeptical Science’ web site (http://www.skepticalscience.com/global-warming-stopped-in-1998-intermediate.htm). Here they show temperature using an unweighted 11-year moving average but do not include data after 2007. The data they do show has a positive trend. (This is strange as that page of the web site has been updated to include a 2011 paper by Foster and Rahmstorf, which we have discussed elsewhere (http://www.climatedata.info/Discussions/Discussions/opinions.php?id=3871334005763196947), which purports to compensate for the effect of solar irradiance, volcanoes and El Nino.)

In the graph below we show the HADCRU3V data set (normalised to 1979 to 2008 for compatibility with satellite temperature data series). We have include three smoothed series: 13 point binomial using the weights in the IPCC report, and 11 point unweighted moving average and a 15 year unweighted moving average.



As can be seen, only the 15 year moving average suggests that temperatures are continuing to rise. At the time of the IPCC report in 2007, the authors were happy with a 13 point smoothing or decadal smoothing. Now that these statistics no longer show a rising trend they are finding new ways of presenting the data to claim that the trend continues. I genuinely believe that rather than moving the goal posts the Met Office would better maintain its credibility by admitting that, at the very least, the rate of temperature rise has slowed. The basic truth of course is that extrapolating from the past climate says little about the future (year on year temperatures are correlated so the temperature in one year does have a bearing on following years).

[The following material was added on 3 February 2012.]

This post was, in part, prompted by the exchange on the Met Office site mentioned above. As part of the moderator's reply he referenced a Met Office document of 2010:
http://www.metoffice.gov.uk/media/pdf/m/6/evidence.pdf

This did accept that the rate of temperature rise in the past decade was slower than in the immediately preceding decades and postulated some tentative ideas as to why this might have happened. However it also contained some other metrics which were presented in such a way as to minimise the impact of this fact. Some of them I have commented on in the blog itself. One of them was a plot of decadal temperatures which showed that, despite the slowdown in the rate of temperature increase, the decade from 2000 to 2009 was the warmest on record. Below we give a plot of the decadal rate of change of temperature in C per year both the for observed temperatures (HadCRU3V annual average values) and the average of 7 climate models combining the 203cm and a1b scenarios to cover the period 1870 to 2010.



This shows two things: that while the rate of rise in the 1990s was the highest on record there were other decades in the past with rises of the same order of magnitude, the models (which get the overall rise fairly accurately) do not represent the rate of rise at a decadal time scale at all well. My purpose in this posting is not to 'rubbish' the models; it is to suggest the selecting data to agree with the science is the wrong approach; it should rather be to admit shortcomings in the science and work on improving it.
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DISTORTION BY DELETION

Recently there has been a thread at Skeptical Science (www.skepticalscience.com) in which they claim that Pat Michaels has distorted the science of climate change by deleting parts of figures. I hold no brief for Michaels and am not intending to comment on the accuracy or otherwise of the claims. However, if the pot is calling the kettle black it had better make sure that it is burnished and spotlessly shining. 

A few months ago I watched Michael Mann’s presentation to TEDx in November 2011, uploaded on 5 December. In it he shows a plot of the predictions of Hansen in 1988. This is from the same source as the graph from which Michaels removed two of the lines. The following slide is from a screen dump of the presentation.



This shows Hansen’s 1988 prediction up to 2019 and observed temperatures up to 2005. Since the presentation was given in November 2011 it would have been possible to include 2010 and, to a high degree of accuracy, the likely value for 2011. In his 2006 paper Hansen also shows his projection with both “station data” and “land-ocean data”. The plot below shows observed data updated to 2011 for both observed records (the 2011 value is provisional) and Hansen's projection digitised from his 2006 paper.



When both data series are included and the data are not truncated to 2005 they tell a slightly different story.
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SHORT TERM VARIATIONS IN TEMPERATURE

In a recent paper Foster and Rahmstorf (F and R, Global temperature evolution 1979–2010) examine the influence of three factors which introduce variability to the temperature record: ElNino/Nina, Volcanoes and Total Solar Irradiance(TSI). They chose to represent the El Nino/Nina effect by the Multivariate El Nino Index (MEI), volcanoes by Aerosol Optical Thickness Data and TSI by sunspot number. They describe their regression as "the multiple regression includes a linear time trend, MEI, AOD, TSI and a second-order Fourier series with period 1 yr." Effectively they assumed the temperature perturbation as the difference from a linear trend plus and allowance for seasonal effects. They chose the period 1979 to 2010 as this included two satellite temperature records in addition to three records based on measurements. They concluded that adjusting the temperature records showed that the underlying temperature trend was upwards for the whole period.

However data for all three variables are available from 1950 and, for some variables, much earlier. We therefore examined the effect of the three factors on temperature from 1950 to 2011.

As we could not assume a linear temperature trend for the whole of the period 1950 to 2011 we calculated the adjustment (or perturbation) as the difference between the three month mean and the 60 month mean. The three month mean represented the short term effect and the 60 month mean the underlying temperature trend. We worked only with HadCRU3V global temperature series. The need to use the 60 month mean means that our series is truncated relative to the F and R series.

The first chart shows the adjustment calculated by this method.


As can be seen the adjustment clearly represents short term effects such as El Nino and volcanoes.

We then regressed the adjustment against the same three variables as F and R. This chart shows a line trend line between the adjustments and the values calculated from the regression equation.The r2 value was 0.3564, a bit lower than the best of the values found by F and R but covering a longer period.



The final plot shows the observed and adjusted temperature series.



For the common period between this plot and that of F and R the results are similar, in particular the effect of 1998 El Nino is reduced but on the other hand the trend is not as uniformly positive as theirs; this is probably due to the use of a different measure of temperature adjustment and the fact that there was no assumption of a linear trend. The plot also shows that in the period up to 1976 the temperature was much flatter than from that year on.

To understand better the differences between F and R and our approach we also tried using the difference from an assumed trend to represent the perturbation. For the period 1976 to 2011 we used a linear temperature increase. For the period 1950 to 1976 we assumed a constant temperature (i.e. completely flat trend).



For the period 1950 to 1976 the two results are virually identical. For the period 1976 to 2011 the results are similar with the use of a linear trend to define the perturbation giving slightly higher values from 2005 onward. The conclusion is that the results show some sensitivity to the method used to calculate the temperature perturbation. It could be argued that a method such as the one we used, which makes no assumptions relative to the underlying trend, has advantages relative to one which does make such an assumption.

(Note: This was first posted on 17 January and revised and extended on 18 January 2012)
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CENTRAL ENGLAND AND GLOBAL TEMPERATURES

On our web site we have a range of climate reconstructions (http://www.climatedata.info/temperature/effects/index.html). One which stands out from the others is the one which was included in the IPCC 1990 Technical Report as Figure 7.1c. This figure is included in Chapter 7.




In the report it is clearly stated that the figures are to be taken as representing global temperature variations. It appears however that the third figure is based on the temperature record for Central England as developed by Lamb (1965). Subsequently a temperature record based on instrumental readings was developed by Gordon Manley (no relation) and others.

The following chart compares that record (downloaded as the file 'cetml1659on.dat') with global and hemisphere temperature estimates produced by the CRU.



As can be seen there is good agreement betwen the Central England temperature record (represent as a 5-year centred moving average), the Northern Hemisphere estimate and, even, the Global one. All the temperature estimates have wide errors bands so perhaps the 1990 figure is not such an outlier as it might appear.
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KOREA - TEMPERATURE

A discussion at Watts up with That (WWUT) (http://wattsupwiththat.com/2011/12/29/uhi-in-south-korea-responsible-for-over-half-of-the-warming/#more-53862)
... reports on a paper which shows the due to its high energy use the effect of the Urban Heat Island in South Korea accounts for much of its apparent rise in temperatures. (Quantitative estimates of warming by urbanization in South Korea over the past 55 years (1954―2008) KIM Maeng-Ki and KIM Seonae )

This posting examines that claim.

The two Koreas have similar land areas, 100,000 km2 for the South and 120,000 km2 for the North. The population of the South, 49 million, is twice the of the North, 24 million. Where they differ most markedly is in their CO2 emissions. From 1990 to 2008 (the last year with data available) South Korea's CO2 emission have increased from 260 million metric tons to 509 million while those of North Korea have fallen from 240 million to 8 million. At WWUT someone has commented it would be nice to compare North and South Korea - and this is what I am about to do.

In the current NCDC average temperature data set there are data for 28 stations in North Korea and 60 in South Korea. From these I extracted 9 stations with long-term data from the North and 11 from the South. Two of the stations in the North went back to 1906 and four stations in the South went back to that year or earlier. In the North the remaining stations were mainly for the period 1961 to present, the critical period for temperature change. Periods of missing data were infilled using data from other stations. In the case of North Korea many stations had gaps for the period 1944 to 1960 (the Korean War) and some years were infilled by reference to stations from South Korea.

The first analysis I carried out was to do a double-mass plot of average cumulative monthly temperature from South Korea against similar values for North Korea.




The plot is an almost perfect straight line. Had temperature for South Korea risen more rapidly than that of the North, due to the urban heat island effect, then the line would have curved upwards from the point when the effect cut in.

I also looked at the tempeature anomaly, with respect to 1906 to 1950, for the two countries.



This shows that temperature in both countries rose at a similar rate. If one assumes that in North Korea, with its minimal energy use (its per capita CO2 emissions at 3.3 t/p/a are 1/3 those of the South at 10.6 t/p/a) there is no heat island effect then it is questionable whther the effect can be as large as the authors of the paper mentioned have concluded.

As a caveat I should mention that my sole criteria for choosing stations was length of record and I only used data from the NCDC data base. It may be that the authors had access to larger data base of South Korean data.
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SITE COMMENTS

This is where you can comment on our site. Is there other data you would like to see? Do you have comments on the data we have presented or the way we have described it? Have you found and errors in the data, And, of course, words of thanks or encouragement would also be appreciated.

At the RealClimate blog blog there have been comments on this site. Whilst I have addressed many of them as comments in that blog, to deal with them fully needs more space than the moderators are likely to allow. So I am addressing them here. The thread was essentially about the analogy between convincing people about the reality of a heliocentric universe and that of convincing people about the reality of climate change. I commented that it could be instructive to study why once widely accepted scientific views fell into disregard. Another commentator followed the link to this site and a discussion about this site then ensued.

Two of the commentators felt that the aim of this site was to promote a 'sceptical' agenda. I disagreed. The site has no 'agenda' but is rather an examination of data surrounding climate.

Comment#67 said:

";[the site is ] not about ‘climate change’ and promoting a particular perception of it
It seems to be about obscuring a particular perception, rather.
I’m just poking at one of the blatant issues, not reviewing the whole site, which as others noted has pages and loads of subtle spin and distortion.
You claim that if you knew the Milankovich contribution it might change how you think — but you know the Milankovich forcing is trivial compared to CO2 and you omit that.
How do you justify not informing people about the rate of change?
Would you provide the relevant information if that were professional work? Surely how fast a change happens and how large it is relative to other changes would be important information to provide."

It is widely accepted the earth moves out of an ice age when the coincidence of cycles gives a maximum of solar radiation at 65 degees north in July. There is however no generally accepted theory of why this should be so. It is of course true that the changes in radiation linked to the Milankovitch effect, over millennia, are in no way linked with current climate change, over decades. However the increase in temperatures observed by thermometers over the last century and a half does not follow a smooth trend. Sixty five degrees north is a band of latitude where a higher proportion of the earth’s circumference is covered by land than elsewhere. It is also covered by boreal pine forests which have a high difference between summer and winter albedo and is a band where melting permafrost releases methane. Understanding these issues in relation to Milankovitch cycles could clearly lead to a better understanding of climate change.

We do of course provide information on the rate of change of temperature (and snow cover, sea level, cyclones etc.)

Comment#68 said:
"You say these days everyone is either sceptic or warmist and go on to say that you are no sceptic (because you do not falsifying data, although you do come to some contrarian conclusions).
Your website however is strongly sceptical. Whether its ‘climate data’ or ‘climate change,’ its still sceptical. If the views expressed there reflect your own, then you are indeed a sceptic. Giving primacy to WUWT in your climate blog search function, using PIPS to underplay the loss of Arctic sea ice, presenting graphs & text on snow cover that a sceptical propagandist would be proud if. Those were the three pages I visited earlier that rang alarm bells. Elsewhere I note that your only concern with burning fossil fuel is in not running out of the stuff. In my book, that’s a bit of a clincher.
You may deny being a sceptic but I see scepticism as being in denial about a whole lot of stuff, so denying being a sceptic would not come as that much of a surprise."

WUWT is at the top of our list as it happens to be currently the most popular.

In the description of ice thickness using PIPS I comment on the fact whilst the ice area rebounded after 2007 the thickness and volume did not and this gave credence to those who pointed out that whilst the ice area may have recovered it was 'rotten'.

I preset a graph of long term Arctic ice estimates from 1870 which shows a steady decline since the 1960s. I also make it clear that whilst Antarctic sea ice is increasing the decrease in Arctic sea ice is larger. The graph on global snow cover, which you specifically object to is, as far as I can tell, an accurate reflection of the global picture. That snow cover is reducing at a steady rate.
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PRECIPITATION AND EL NINO

Recently there has been a number of blog postings linking temperature and El Nino. Tamino (http://tamino.wordpress.com/2011/12/06/the-real-global-warming-signal/) based on a paper by Foster and Rahmstorf used the link to show that global warming had not levelled off. Meanwhile Frank Lansner at WUWT did a similar analysis to show that there had been a levelling off.

One thing which always surprises me is the importance given to temperature by comparison with that given to precipitation. This is very much the case with the previous IPCC report and I am posting it here in the hope that this will change. Within certain wide limits what matters to people is not temperature, and by inference evaporation, but the balance between evaporation and temperature.

The following graph shows a regression plot of precipitation and an El Nino index. The precipitation is based on the NCDC global precipitation anomaly with a 5-month centred moving average. The El Nino index is the NOAA's Oceanic El Nino Index (ONI).



This shows that global precipitation and El Nino are correlated.

The next plots shows the variation in precipiation and the ONI. The precipitation is as above and the ONI is inverted (i.e. the original value multipied by -1).



As can be the two are closely related in both magnitude and timing. The fact that the two are synchronous suggests that neither is forcing the other but that both are a result of a common factor.

In TAR4 very little information was given on the simulation of precipitation by climate models. One of the reasons might have been the fact that the models did not represent the sort of variations shown above.

This should be addressed in TAR5.
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IPCC TECHNICAL ASSESSMENT REPORT 5 – THESIS 3

Thesis: The presentation of sea ice in TAR4 used only a sub-set of the data. It should use a wider range of data with reference both to data which were available at the time of TAR4, and data which have become available since.

The technical summary presents the following set of graphs:



The way the graphs are presented is reminiscent of graphs of return on investment of rivals presented by some of the less honest financial intermediaries. Those for the Arctic are presented as anomalies with a scale set so that the full range fits in the rectangle and it seems as if ice extent has fallen close to zero. For the Antarctic, where the area of ice has been tending to increase, they have used the same scale which conveniently minimises the increasing tendency of Antarctic ice.

The following graph presents the same data, updated to May 2010, but as extent not anomalies.




This very clearly shows that on average there are similar areas of sea ice in the Arctic and Antarctic, that the variation is much larger in the Antarctic than the Arctic and the loss of sea ice in the Arctic is only partially balanced by the gain in the Antarctic. A linear regression through the average values suggests that the Arctic has lost 50,000 km2 per year whereas the Antarctic has gained 14,000 km2 per year. The average total area of sea ice 23.9 million km2 so this loss represents a rate of 0.15% a year.

The Synthesis Report also mentions the break-up of the Larsen B ice shelf. This was an area of ice partly floating and partly resting on land and joined to the main Antarctic ice shelf. It was located on the most northerly (i.e. warmest) point of the Antarctic. The area of the ice shelf was 3250 km2 and its weight was 72 billion tons. The loss of the ice shelf has become iconic and it has been compared to the area of Rhode Island or to the trillions of 20 lb bags which could be filled (though not in the IPCC report). In relation to the area of the Antarctic ice sheet it represents only 0.02% of the area or 0.003% of the volume.

We do recognise that the minimum area of sea ice is a useful metric. The albedo (reflectivity) of ice is high and that of sea water is low. In summer, when ice is at a minimum and sunlight at a maximum, the albedo effect is important and the fears that the low Arctic minimum of 2007 could lead to a progressive reduction in sea ice area were valid.

At the time of the TAR4 there was little information available on ice depth and volume. From October 1998 daily values of ice thickness are available from the US Navy polar ice prediction system(PIPS). The forecast values of ice thickness use weather forecasts, and buoys and ice concentration data from the Special Sensor Microwave Image (SSM/I) are used to initialize the system's forecast. The results are available as GIF images. A typical one is given below.





To derive areas and volumes the graphic images were downloaded analysed. The projection used is not an equal area project so the areas derived were approximate. They were based pro-rata on a scanned image of Greenland. During the analysis it was found that the colours representing thickness range 0.5 to 0.75 were never present. It should also be noted that occasionally there were anomalous values, for example for a few days the Caspian and Aral seas were included.

The following graph shows the area and volume of sea ice from October 1998 to May 2010. These figures only apply for ice greater than 0.75 m thick and consequently the areas are less than those of ice extent in the above graph.





In general the volume and area show similar variation but after the low summer minimum of 2007 the ice area recovered well in 2008 but the volume. This is reflected in the chart on ice thickness.





This shows that minimum ice thickness was less in 2008 than in 2007, giving some support to those who said the ice that year was “rotten”. It is interesting to note that the ice thickness is bi-modal; one maximum occurs in May when the ice area has just passed its maximum and the second in September near to the point when it is at its minimum. This can be seen more clearly in the following graph where compare average thickness with current ice thickness.

The shape of the graph suggests that ice thickness is belatedly reaching its spring maximum. How it will develop in the coming months is something we will follow with interest. What these graphs do show is that Arctic sea ice is recovering in terms of volume, are and thickness.



In these “theses” we generally do not concern ourselves with short term effects so to counter that remember that during the last inter-glacial sea levels were 6 m higher than at present. Although melting sea ice does not affect sea levels we can none-the-less expect more melt independent of any anthropogenic effect.

IPCC TAR5: The presentation of graphs data in TAR5 was biased to give an exaggerated impression of ice loss. In TAR5 the presentation should be more balanced. It should use a wider range of metrics to assess changes in sea ice.
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IPCC TECHNICAL ASSESSMENT REPORT 5 – THESIS 2

Thesis: That the discussion of sea level rise in IPCC TAR4 has much to recommend as a model for other topics.

Those of you who have already seen our first thesis, on global temperatures, may have got the impression that we were out to ‘get’ the IPCC. This is not the case. We are self-financed and have no agenda. As we say on our Home Page: “We are trying to prove only one thing: rational debate is possible when participants have access to the facts.”

In TAR4 the increase in sea level is presented in the following graph.





This graph appears as Figure 3 in the Summary for Policy Makers and elsewhere (We have extracted the sea levels from a compound graph which also showed Global Average Temperatures and Northern Hemisphere snow cover). It combines levels from tide gauges (circular dots) and satellite measurements (the red line).

In the summary the accompanying text says: “Global average sea level rose at an average rate of 1.8 [1.3 to 2.3] mm per year over 1961 to 2003. The rate was faster over 1993 to 2003: about 3.1 [2.4 to 3.8] mm per year. Whether the faster rate for 1993 to 2003 reflects decadal variability or an increase in the longer term trend is unclear.” Similar words appear in the Technical Summary and the Synthesis report. What is commendable in this case is that even in the condensed Summary for Policy Makers there is no attempt to attach a high level of significance to the higher rate of sea level rise for the ten years preceding the preparation of the report.

The Technical Summary also states (Paragraph 3.3.3): “The tide gauge record indicates that faster rates similar to that observed in 1993 to 2003 have occurred in other decades since 1950.” This is supported by the following figure in Chapter 5 of the main report.





This contrasts markedly to the global temperature graph we discussed in the previous ‘thesis’. (http://www.climatedata.info/Discussions/Discussions/opinions.php?id=5404421343497121129 ).

There are two areas where the increase could be presented in a wider context in TAR5.

Firstly since TAR4 was written there is more evidence of sea level changes in the last couple of thousand years.





The blue crosses represent relative sea level rise for Vidarholmi in Iceland as calculated by Gehrels et al. No adjustment has been made for post glacial rebound but this is unlikely to have varied substantially over the period of the estimates. The figure before 100 AD may have been modified by compression in the salt marsh sampling area but even so the levels after that date suggest that recent rates of rise are by no means extraordinary.

The green circles show estimates of sea level on the coast of Israel calculated by Sivan and Toker. They are based on archaeological evidence from different broadly defined time periods (e.g. Hellenic or Crusader). The dating and levels are not given to a high degree of accuracy but also suggest that rapid sea level changes might have occurred in the past.

The red line, provided for comparison, is the increase since 1702 based on tide gauges by Jevrejeva et al. This confirms that the rate of sea level increase accelerated around 200 years ago and is not a recent phenomenon.

The second point is that in the previous interglacial sea levels were about 6 m higher than they are today and in other interglacial periods levels were from 3 m to 20 m higher. It is therefore possible than in coming centuries many coastal locations on earth might experience sea level rises of the same order of magnitude as those estimated by Sivan and Toker. That said there are many coastal cities in the world, such as Marseilles, Akko (Acre) and Naples, which existed well before the start of the present era and which have adapted to sea level changes.

IPCC TAR5: The TAR4 dealt with sea level changes accurately and in a responsible way. However the IPCC TAR5 could be improved by expanding information on the context of the projected level changes.

References:
Gehrels et al., Rapid sea-level rise in the North Atlantic Ocean since the first half of the nineteenth century. The Holocene 2006; 16; 949

Shivan and Toker, The Sea’s ups and downs. http://newmedia-eng.haifa.ac.il/?p=2330

Jevrejeva, S., J.C. Moore, A. Grinsted and P.L. Woodworth. 2008. Recent global sea level acceleration started over 200 years ago?, Geophysical Research Letters, 35