Sunday, February 10, 2013

A climate of scepticism - Part II


The first part of this piece described the weakness of the hypothetical link between increasing carbon dioxide and increasing global temperatures.  In this part, I consider the question of whether there are models which can strengthen the hypothesis and whether those models can tell us anything about other aspects of climate such as rainfall.

The proponents of the anthropogenic warming thesis claim to have models that show how added carbon dioxide will lead to a warmer world[i].  There are major problems with these models, not least of which is the fact that the proponents claim that doubling the CO2 in the atmosphere will increase the temperature by over 3oC. This is well above any physical reason[ii]. It results from arguments about the effect of water vapour in the atmosphere, which is supposed to exacerbate the effect of increased CO2. 


The doubling effect is so far invisible.  Other estimates have suggested that doubling the CO2 may increase the global temperatures by less than 1oC[iii].  The evidence for this is building. For instance, there has been about a 40% increase in atmospheric CO2 since 1945, which would imply perhaps 1.2oC of warming if doubling the CO2 caused a 3oC rise.  Figure 1 in the previous posting showed that the actual warming over this period has only been about 0.4oC. Has the globe cooled by 0.8oC while the added CO2 has been warming us? It seems unlikely.


There are further reasons to doubt the models.  For instance, Figure 5 reproduces Figure 10.7 from the IPCC Fourth Assessment Report[iv]. The sections are from the South Pole on the left to the North Pole on the right.  In the atmosphere, altitude is expressed in terms of pressure, with sea level at 1000hPa and 11km being about 200hPa. Stippling on the figures shows regions where all the models agree within narrow limits.
Figure 5. Model predictions of global temperature changes: atmospheric upper, oceanic lower


The area of particular interest is the ‘blob’ in the atmosphere over the equator and centred at about 200hPa. In 2011-2030 it is just less than 1.5oC above today’s ground level temperatures. By 2046-2065 it is expected to be about 3oC warmer, and by 2080-2099 about 5oC warmer. Thus this region is expected to warm by about 0.6oC per decade, if the models are to be believed.


For about the last 60 years, balloons carrying instruments have been flown into this region to obtain data for weather forecasts.  Examination of the temperature records has failed to reveal any heating whatsoever[v].  Satellites have been flown since the late 1970’s, and some of their views through the atmosphere can be interpreted as average temperatures of particular regions[vi].  The satellites show very slight warming – but nothing like 0.6oC per decade.


In science, a single experiment can suffice to disprove a theory.  Any theory whose predictions fail experimental tests must be abandoned without further ado. In the present case, the anthropogenic warming hypothesis has led to theoretical models, but those models have failed experimental proof.  Such is the strength of belief in the anthropogenic thesis, however, that the modellers are most reluctant to abandon – or even revise – their models. This is one of the strongest reasons for scepticism.


The anthropogenic thesis has also led to many predictions of the possible conditions in a warmer world.  Some, such as the impact on the cryosphere, seem to be borne out. However, the models which, as noted earlier, are highly suspect, suggest such things as dramatic changes in precipitation.  The evidence is negligible.


For instance, there is a very long record of rainfall for England and Wales, shown in Figure 6[vii]. There is absolutely no sign of any change in the rainfall pattern over the last 60 years. Over the entire period, the annual average over 25 years is 913 ±42mm. The 42mm is the maximum deviation, not the standard deviation!

Figure 6. A 240-year rainfall record

Similarly, there are repeated suggestions that the sea level will increase rapidly due to the melting of ice and the warming of the oceans (warm water is less dense than cold, so it occupies a larger volume).  It is true that the sea level is rising, but you seek in vain for any evidence that it has risen significantly faster since 1945 than before.  Figure 7 illustrates this, using the tide gauge data from New York which extends back to 1858 with a gap from 1879 to 1892[viii]. The regression line for all the data from 1870 to 2011 has a slope of 2.947mm/a; that from 1945 to 2011 has a slope of 2.948mm/a.  There has been no significant increase in the rate of sea level rise at New York for the past 140 years.

Figure 7. A 150-year sea-level record.


Many of the fears about sea level rise are unfounded.  Yes, the sea is rising slowly.  Satellite measurements since the early 1990’s confirm a rate of rise of about 3mm/a[ix]. However, there are already defences against the sea. It is necessary to allow for tides, storm surges and even tsunamis.  The existing defences are measured in metres, not mm. An increase in the average level of 3mm/a can be offset by raising the defences by an additional brick every 30 years or so. The rising sea level is not a threat.


Of course, there are events where the defences prove inadequate.  This was the case when Hurricane Katrina struck New Orleans.  Several years previously, it had been reported that the levees were likely to fail[x]. They were old, and lacked modern design features. They failed, as anticipated, when the storm surge arrived. Their failure had nothing to do with ongoing rise in sea levels, and everything to do with weak defences. 

However, there are repeated references in the literature to the New Orleans levee failure being the result of “climate change.” This illustrates a feature of the debate that reinforces scepticism.  Disasters that have nothing to do with a changing climate are ascribed to “climate change” as a means of raising awareness about the supposed threats. Do we need to have our awareness raised? Or isn't it better just to be sceptical? 

[i] Randall, D.A., R.A. Wood, S. Bony, R. Colman, T. Fichefet, J. Fyfe, V. Kattsov, A. Pitman, J. Shukla, J. Srinivasan, R.J. Stouffer, A. Sumi and K.E. Taylor, 2007: Climate Models and Their Evaluation. In: Climate Change 2007: The Physical Science Basis. WG1, Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S. et al, (eds.)]. Cambridge University Press, Cambridge
[ii] See Randall, D.A. et al, op cit p. 640: “A number of diagnostic tests have been proposed…but few of them have been applied to a majority of the models currently in use. Moreover, it is not yet clear which tests are critical for constraining future projections (of warming). Consequently, a set of model metrics that might be used to narrow the range of plausible climate change feedbacks and climate sensitivity has yet to be developed.”
[iii] Spencer, R.W. and Braswell, W.D  Potential Biases in Feedback Diagnosis from Observational Data: A Simple Model Demonstration, J Climate 21 5624-5627, 2008 DOI: 10.1175/2008JCLI2253.1
[iv] Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper, I.G. Watterson, A.J. Weaver and Z.-C. Zhao, 2007: Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. WG1, Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., et al (eds.)]. Cambridge University Press, Cambridge
[v] Douglass, D. H., Christy, J. R., Pearson, B. D. and Singer, S. F. (2008), A comparison of tropical temperature trends with model predictions. Int. J. Climatol., 28: 1693–1701. doi: 10.1002/joc.1651
[vi] Spencer, R.W. and Christy, J.R. 1992: Precision and Radiosonde Validation of Satellite Gridpoint Temperature Anomalies. Part I: MSU Channel 2. J. Climate, 5, 847–857.
doi: http://dx.doi.org/10.1175/1520-0442(1992)005<0847:parvos>2.0.CO;2 Accessed January 2013
[ix] http://sealevel.colorado.edu/ Accessed January 2013
[x] Fischetti, M. Drowning New Orleans. Scientific American, October 2001, pp34-42
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Thursday, February 7, 2013

A Climate of Scepticism - Part 1



I recently had a piece in Anthony Watt's  Watts Up With That blog.  It attracted a few hundred comments, which was gratifying.  It was written in ordinary language, so used some inexactitudes because I felt that communication was more important, in this case, than precision. Some suggested it should be republished elsewhere - so this is the first part of a long story.

The world has been getting slightly warmer.  Of that there is little doubt.  The measurements by which we know that it is warming are poor.  The figures are not accessible, and keep on changing[i].  Many points at which temperature is measured are badly sited, and bound to give misleading results[ii].  Nevertheless, almost everyone agrees that the world is warmer today than it was 150 years ago.

There are some fairly clear signals of a warmer world.  The Arctic ice is less than it was[iii]. Many glaciers are retreating[iv].  Some glaciers – for instance, those on Kilimanjaro – are shrinking because the long-term precipitation is less than it was 150 years ago, not because it is warmer[v]. Others seem to be shrinking from a warmer climate. There are, however, little data on this[vi].

Where the sceptic differs from many other scientists is in ascribing the warming to human activities – specifically, the burning of fossil fuels and the concomitant rise in the carbon dioxide concentration in the atmosphere.  The hypothesis is that the carbon dioxide traps infra-red radiation that would otherwise escape to space.  This means that some of the energy received from the sun is not lost, and the trapped energy leads to a warming of the globe. 

The physics of how carbon dioxide traps infra-red radiation is well known[vii].  But there are other molecules in the atmosphere that also trap infra-red radiation.  Water vapour is the predominant “greenhouse gas”[viii]. What is not so clear is the extent to which the trapping of energy causes heating.  There are wonderful mathematical models that claim to show how heating occurs.  Unfortunately, all the models suffer from identifiable flaws, a point considered later.

A prime difficulty with the anthropogenic warming thesis is that it is not known how much of the warming is natural and how much might be caused by carbon dioxide.  It is simple to illustrate this. Figure 1 shows the global temperature record as kept by the Climate Research Unit at the University of East Anglia[ix].
Figure 1 Global temperatures, relative to 1950-1990 average

The global temperature dropped from 1850 to 1860; rose until 1880; dropped until 1910; rose until 1945; dropped until 1980; rose until 2000; and has dropped slightly since then.

Figure 2 shows the carbon dioxide record. Careful measurements have been made at Mauna Loa on Hawaii since 1958[x].  The pre-industrial level of CO2 in the atmosphere is generally accepted to have been about 280ppm[xi]. Figure 2 shows a reasonable extrapolation of the data back to about 280ppm in 1800.

Figure 2 Atmospheric CO2 concentrations, measured and estimated.

It is a reasonable assumption that the measured rise is the result of fossil fuel consumption.  Figure 3 shows annual CO2 emissions over time[xii].  It only exceeded 5 billion tons per annum in the later 1940’s.  Thereafter it grew rapidly, passing 10 billion tons in 1963, 15 billion in 1971, 20 billion in 1986 and 30 billion in 2006.
Figure 3 Annual CO2 emissions from fossil fuel consumption.
Comparison of Figures 2 and 3 makes it clear that the rise in atmospheric carbon dioxide is very likely directly related to the emissions from fossil fuels.  However, the low levels of emissions up until about 1945 make it clear that the impact of the fossil fuel combustion prior to 1945 must have been very small if not negligible.  Therefore the changes in global temperatures prior to 1945, shown in Figure 1, were largely natural. The additional carbon dioxide from human activities cannot have played a significant part in the changes prior to 1945.

If most of the temperature changes before 1945 were largely natural, then there is great difficulty in determining how much of the temperature change after 1945 is natural and how much might be driven by increasing carbon dioxide.  This raises the question of what the natural variation in temperature might be.

To answer this question, consider the Vostok ice core record over the past 9000 years[xiii].  The core was sampled every metre of depth, which represented ~20 years of accumulation in the upper layers and ~50 years in the lower levels.  The temperature was estimated from differences in the oxygen isotope ratios.  While a point measurement such as this cannot give a good measure of the average global temperature, it is a reasonable measure of changes in global temperature, and it is primarily temperature changes that are of interest.

The data are shown in Figure 4. There has been a slight cooling over the past 9 millennia, as shown by the least-squares line.  The data were therefore detrended before further analysis – the mean temperature at any one date was added to the reported relative temperature.  The detrended temperatures were what is known as “normally distributed”, i.e. there was nothing abnormal or skewed about them. Then the rate of change between each detrended temperature and the temperature approximately 100±20 years earlier was calculated and expressed as a rate per century.  The results were also normally distributed, with a standard deviation of 0.94oC per century.

Figure 4. Relative temperatures over the past 9000 years.

Thus there is about a 2:1 chance that the temperature may vary by up to 1oC per century from natural causes, but only about a 1 in 10 chance that it will vary by more than 1.9oC naturally. Between 1900 and 2000, it varied by about 0.9oC, which is therefore within the range of natural variation.

And that, in simple terms, is why there is scepticism about the thesis that carbon dioxide is causing global warming – there is no clear signal of any such warming effect.

[iv] Paul, F., Kääb, A. and Haeberli, W. Recent glacier changes in the Alps observed by satellite: Consequences for future monitoring strategies, Global and Planetary Change, Volume 56, Issues 1–2, March 2007, Pages 111-122, ISSN 0921-8181, 10.1016/j.gloplacha.2006.07.007.
(http://www.sciencedirect.com/science/article/pii/S0921818106001603) Accessed January 2013
[v] Mölg, T., and D. R. Hardy (2004), Ablation and associated energy balance of a horizontal glacier surface on Kilimanjaro, J. Geophys. Res., 109, D16104, doi:10.1029/2003JD004338.
[vi] UNEP Global glacier changes: facts and figures. World Glacier Monitoring Service, 2008
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