The table below lists prominent volcanic eruptions since 1815. They were compiled from Robock [1] and Zielinski et al. [2].  Besides the date and the name of the volcano is given the Volcanic Explosibility.Index (VEI) and the Dust Veil Index (DVI) which are measures of the possible climatic disturbance of the eruption. Also is given the sulphate measurement from the ice core studied by Zielinski et al. which is a measure of the sulphur contribution to the atmosphere.

It will be seen that there were far more large volcanic eruptions towards the end of the nineteenth century, and at the beginning of the twentieth century than at any time since.  It appears, from the study of early temperature records [3] that this period was unusually cool; and it seems probable that the high level of volcanic activity contributed to. this coolness. It would seem inappropriate to select this exceptionally cool period as a datum line by which to evaluate the possible existence of global warming by the greenhouse effect. Recently the behaviour of the atmosphere following the eruption of Mount Pinatubo in 1991 has been adduced as evidence for the lack of global warming, but it seems to have been forgotten that the beginning region of the global temperature records used to evaluate supposed global warming included eruptions such as those of Krakatoa (1883) and several others.

It should be pointed out that the Volcanic Explosibility Index (VEI) and the Dust Veil Index (DVI) are rather crude measures of volcanic activity. It would seem, from the ice-core measurements, that several recent, but apparently less violent eruptions, may have provided large amounts of sulphur gases.

Although there has always been a belief that volcanic eruptions lead to reduction in global temperature, there has been until recently  surprisingly slim evidence for this belief. For example, the eruption of the volcano Tambora on the Indonesian island of Sumba in April 1815, which has been called “the largest and deadliest volcanic eruption in recorded history” has been held responsible for the “Year without a Summer. of 1816, when temperatures were unusually low all over the globe. Yet, as has been shown by Angell and Korsover [4], the eruption came at the end of several years of falling temperatures, as measured at several places, and it was followed by immediate temperature rises for all of them, except for the measurements at Yale University where the rise was delayed by only a year.

A more recent example was the eruption of El Chichon in April 1982 which was followed by the record breaking hot year of 1983, 0.21ºC above 1982.  Although there are also examples of temperature falls following major volcanic eruptions, they are only slightly in excess of the rises [5].

The possible effects of volcanic eruptions on climate were almost totally ignored by the IPCC in their Report “Climate Change.6″ in 1990. The only mention of them was as a possible contribution to “natural variability”. Angell [7] has presented evidence that global cooling from volcanic eruptions can usually be demonstrated if the temperature data are corrected for the influence of the El Niño Southern Oscillation which has a comparable effect on climate to volcanic eruption, and thus may cancel it or enhance it.

The attitude of the IPCC to the influence of volcanic eruptions underwent a change before the publication of the “Climate Change 1992. supplementary Report, as the result of the eruption of Mount Pinatubo in the Philippines in June 1991. This eruption could be studied in much greater detail than any previous one, by satellite and other instruments. It was calculated that the negative radiative forcing associated with the  eruption of Mount Pinatubo exceeded the magnitude of the positive forcing associated with greenhouse gases during the second half of 1991, and remained significant through 1991 and much of 1992 [9.10,11].

The effects seem, however, to have dispersed by the beginning of 1994. The temperature effects are evident in the record of the NASA Satellite Global Monthly Temperature Anomalies from January 1979 to December 1994.

It will be seen, to begin with, that there has been no distinguishable overall change in global temperature over this whole period. It is also apparent that immediately after the eruption of Mount Pinatubo in June 1991 there was a rise in temperature of 0.2.ºC. Then, from August 1991, there was a fall of 0.7ºC until August 1992, when there was a rise of 0.3ºC by January 1993, followed by another fall of 0.3C by January 1993, a further drop of 0.3ºC by May 1993, and then a rise of 0.55ºC by January 1994.

This complex behaviour has been oversimplified by McCormick et al [9].  If the 12 month running means are taken, there was a drop of 0.45ºC between October 1991 and June 1993, followed by a rise of 0.25ºC by December 1994. But were all of these changes due to Mount Pinatubo? It should be noted that the fall in temperature between December 1988 and January 1989 of 0.7ºC is not attributable to volcanic action; and we still have the temperature rise after El Chichon in 1982 as a contrary example.

The apparently large temperature drop after the eruption.of Mount Pinatubois less evident in annual or monthly figures. The annual global temperature anomalies from Jones et al.12 are 1990, 0.39ºC, 1991, 0.35ºC, 1992, 0.17ºC, 1993, 0.21ºC and 1994, 0.31ºC. Since Pinatubo erupted halfway through 1991 it can hardly be held entirely responsible for the 0.18ºC drop from 1991-1992, and subsequent to that the temperature has crept up slightly. It is considered that the 1994 figure is no longer influenced by Pinatubo. Mount Pinatubo has therefore not had the profound effect on the climate that was predicted, and it seems that any measured effects have now dispersed.

REFERENCES

1. Robock, A., “The Volcanic Contribution to Climate Change of the Past 100 Years”, in ” Greenhouse Gas-Induced Climate Change “(Ed M.E. Schlesinger) 1991, Elsevier, pages 429-443

2. Zielinski, G.A., et al. 1994, “Records of Volcanism Since 7000 BC from the Greenland Ice Core.” Science, 264, 948-951.

3. Weber, G-R., 1994, “Long-Term European Temperature Variation Between 1525 and the Present”, “Proceedings of the Air and Waste Management Association Conference on Global Climate Change.” (C.V. Matthai and G. Stensland, Eds.), Phoenix Arizona
5-8 April pages 120-157.

4. Angell, J.K., and Korshover, J., 1985, ”J. Climate  and Applied Meteorology” .24,937-951.

5. Stommel, H and E., 1979 “The Year without a Summer”, “Scientific American”,  240, 134-141

6. Houghton, J.T., Jenkins,G.J., & Ephraums, J.J. (Eds.) 1990, “Climate Change: The IPCC Scientific Assessment”. The Intergovernmental.Panel.on Climate Change. Cambridge University Press .

7. Angell, J.K., 1988. “Impact of El Ni<\q>o on the Delineation of Tropospheric  Cooling Due to Volcanic Eruptions”. “J. Geophysical Research”, 93, 3697-3704.

8. Houghton, J.T., B.A. Callander, and S.K. Varney. 1992. “CLIMATE CHANGE 1992: The Supplementary Report to the IPCC Scientific Assessment. “Cambridge University Press

9. McCormick, M.P., Thomason, L.W., & Trepte, C.R., “Atmospheric Effects
of the Mt Pinatubo eruption”, 1995, “Nature,” .373, 399-404.

10. Minnis, P.,  et al., 1993, “Radiative Climate Forcing by the Mount Pinatubo Eruption”. “Science” 259, 1411-1415.

 11. Dutton, E.G., and Christy, J.R., 1992. “Geophys. Res. Letters” 19, 2313-2316.

12. Jones, P.D., Wigley, T.M.L., and K.R. Briffa, 1994, pp 603-608 in T.A. Boden, D.P. Kaiser, R.J. Sepanski and F.W. Stoss (Eds) “Trends ’93″  Carbon Dioxide Information Analysis Center, Oakridge, Tennessee

This article was written by Vincent Gray of Wellington, New Zealand, in March 1995 and is republished here with his permission.

Dr Vincent Gray explains why, and begins at the very beginning with an explanation of “temperature” and how it is measured:

TEMPERATURE is one of the six basic units of the SI (Metric) system, but is the least understood  and most mysterious of all of them.

It originally arose as a method of assessing heat level, which could be measured by the change in length of a liquid inside a glass capillary. The scale was divided into a number of equal units between “fixed” points.

In 1724, Daniel Gabriel Fahrenheit chose three fixed points. Zero was the temperature of a mixture of ice, water and ammonium chloride, which he considered to represent the lowest possible temperature on the earth’s surface (he was wrong). Then he chose the melting point of ice as 32 degrees, which meant the boiling point of water was 212 degrees. It is amazing that this cumbersome and inconvenient system survived for so long, and is still used in the USA.

In 1742, the Swedish astronomer Anders Celsius devised a temperature scale based only on the melting and boiling point of water, with the movement of a liquid in a glass capillary divided into 100 degrees. He took boiling point as zero and the melting point as 100.  Celsius originally called his scale centigrade derived from the Latin for “hundred steps”. For years it was simply referred to as “the Swedish thermometer”. 

The scale was later reversed by Carolus Linnaeus in 1745, a year after Celsius’s death, to how it is today. I was personally rather surprised when the name “Centigrade’ was changed to “Celsius” as it seemed to involve a reversal of the scale, but fortunately, did not.

A better understanding of temperature was a result of the development of the science of thermodynamics in the middle of the 19th century. It was realised that different forms of energy were equivalent, and were interconvertable, at least in their ultimate conversion to heat energy.  Heat energy, such as that produced chemically could only be partially converted to mechanical energy because of the necessary operational requirements of engines.

It became evident that mechanical and vibrational energy of atoms and molecules in all substances is the source of heat energy, so that temperature can be related to the average of this energy. Since this energy disappears altogether at the absolute zero the SI temperature scale sets its origin at the absolute zero and calls the scale degrees Kelvin.  On the Celsius scale the absolute zero is -273.15 degrees. This is zero degrees on the Kelvin scale.

According to thermodynamic theory, the temperature of any body can only be defined if that body is in equilibrium, that is to say it is neither receiving energy or losing it. Any body that is not in equilibrium does not have a definable temperature. It is somewhat paradoxical that the rigid definition applies as a result of averaging the many different amounts of mechanical energy within the body but cannot be applied rigorously if there is a variability.

There is nowhere on the earth, or in its atmosphere, where the energy content can be considered to be in equilibrium. In daytime there is usually a rise in energy, at night time, a fall. There are no circumstances where a definite temperature of any part can be defined thermodynamically.

You can, of course, put a measurement instrument close to one part and record the apparent transient temperature. If the measurement is continuous you might even derive some sort of average temperature at that point. But there is no way that one could carry out sufficient measurements, distributed in a representative way, so that any sort of global average temperature could be derived.

The climate scientists connected with the IPCC do, however, claim not only that they have measured average global temperature, but that this has been carried out with such accuracy that an increase of less than one degree Celsius over 100 years could be confidently related to increased emissions of greenhouse gases over the period, rather than to the errors of the measurement.

James Hansen, the pioneer scientist who is credited with having launched this belief in the influence of increasing greenhouse gases and continues to promote it, has admitted publicly, on his website that the measurements are completely unreliable:

When asked what is meant by Surface Air Temperature (SAT) Dr Hansen explains: 

“I doubt that there is a general agreement how to answer this question. Even at the same location, the temperature near the ground may be very different from the temperature 5 ft above the ground and different again from 10ft or 50ft above the ground. Particularly in the presence of vegetation (say in a rain forest) the temperature above the vegetation may be very different from the temperature below the top of the vegetation. A reasonable suggestion might be to use the average temperature of the first 50ft of air either above ground or on top of the vegetation. To measure SAT we have to agree on what it is and, as far as I know, no such standard has been adopted. I cannot imagine that a weather station would build a 50ft stack of thermometers to be able to find the true SAT at its location.”

When asked what is meant by daily surface air temperature, Dr Hansen explains:

“Again, there is no universally accepted correct answer. Should we note the temperature every 6 hours and report the mean, should we do it every two hours, hourly, have a machine record it every second, or simply take the average of the highest and lowest temperature of the day? On some days the various methods may lead to drastically different results.”

When asked what the media report when they refer to surface air temperature, Dr Hansen explains:

“The media report the reading of one particular thermometer of a nearby weather station. This temperature may be very different from the true SAT even at that location and has certainly nothing to do with the true regional SAT. To measure the true regional SAT we would have to use many 50ft stacks of thermometers distributed evenly over the whole region, an obvious practical impossibility.”

This rather devastating confession is not even all that can be said. In daytime the surface is warmer than at night time, so that temperatures that are experienced oscillate between two extremes and are hardly ever “average”. Any average is the least probable temperature. This is why meteorologists usually give the daily maximum and minimum rather than the average, since these are the temperatures commonly experienced.

The “temperature anomalies” which form the basis of the “mean annual global temperature anomaly record” are obtained from weather station measurements, only once a day, of the maximum and minimum temperatures of the previous 24 hours.  The number of stations changes over time, the time at which this measurement is taken varies and the actual day is different in different time zones. So-called “corrections” dependent on comparing many neighbouring stations are impossible for most areas. Then the location and influence of surrounding buildings alters over time and is the main reason for a long term upwards bias.

The absence of any scientific justification for the existence of a reliable average global surface temperature is just one of the many absurdities of the assumptions which are made by the basic theory of computer models which assumes that the energy of the earth can be regarded as in equilibrium, with a constant temperature, and sunshine (day and night), and “balanced” with energy coming in equalling that going out. 

Since there is no part of the earth where this “balance” exists, it could not possibly exist on average.

Dr Vincent Gray has been an Expert Reviewer for the Intergovernmental Panel on Climate Change for eighteen years, that is to say, from the very beginning.  He lives in Wellington, New Zealand.

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Hansen, J., 2008a, GISS Surface Temperature Analysis, The Elusive Absolute Surface Air Temperature (SAT) http://data.giss.nasa.gov/gistemp/abs_temp.html