HH Lamb–“Climate: Present, Past & Future–Vol 2”–In Review–Part III

By Paul Homewood

In this final part of Hubert Lamb’s “Climate: Present, Past & Future”, we review what he had to say about the effects of humans on climate. Parts I and II are available here and here.

Again, I would remind readers that everything that follows is based on Lamb’s writings in this volume; any comments of mine will be within [ brackets ]. I would also point out that sections in italics are direct quotations from the book.

Lamb identifies three main factors.

CO2

Lamb was a climatologist, not a physicist, so it is unsurprising that he accepted other scientists’ findings about the warming potential of CO2 and other greenhouse gases. But he does say this

However, as noted in Vol 1, water vapour is an effective absorber of most of the same wave lengths which CO2 absorbs; and Budyko (1974) cites the work of Kondratiev & Niilisk (1963), which suggests from consideration of the effect of the atmospheric water vapour on the absorption of long wave radiation that the changes which have occurred in the amount of CO2 in the atmosphere may have had only a small effect on temperature. …..On balance, the effect of increased CO2 on climate is almost certainly in the direction of warming, but is probably much smaller than the estimates which have commonly been accepted.

Particulate Matter

Lamb has this to say.

Pending more adequate observational evidence, it seems safe to conclude that the effect of man-made dust in the lower atmosphere is mainly in the direction of cooling, and there is probably a tendency to moderate the diurnal and annual extremes of temperature.

Waste Heat (Thermal Pollution)

Rather surprisingly Lamb sees waste heat, (a sort of global urban heat island), as the threat.

Artificially generated heat is significant so far only on a local scale, in the urban heat islands where the surface air temperature in the city centre may average up to 2C higher than in the surrounding country.

An official UN report, (World Energy Supplies), estimated by carrying forward the present the present growth of demand in countries all over the world, that the total output of thermal pollution would rise from 5.5 x 106 megawatts in 1970 to 31.8 MW in 2000.

A further 12 to 15 fold increase is assumed by Budyko, Drozdov & Judin (1966) on the basis of continuity of development by 2050. By that time the output of man-made heat averaged over all land areas would be of the order of 10% of the present average absorption of incoming radiation at the surface (Haefele 1974). As the waste heat output is at present many hundred times larger than average in certain areas and city centres, these would presumably become uninhabitable..

Budyko has suggested many times that man’s output of heat is likely to become the most serious cause of change of climate within about 100 years.

Summary

Lamb sums up these and other man-made influences.

The various ways in which man has polluted the atmosphere and disturbed the environment so far have probably not individually affected the general level of prevailing world temperatures by more than 1 to 2 tenths of a degree.

Complementary to these conclusions, a theoretical modelling study by Schneider & Mass (1975) gives fresh ground for believing that the observed changes of global average surface air temperature from 1880-1970 could be rather well explained by the combined effects of volcanic activity and solar variations.

The projections of the various items due to human activity and their effects, both positive and negative on world temperature into the future, however, commonly tend to exponential increase. Forward estimates of their net effect are therefore unstable, but it appears likely that the increasing output of man-made heat will gain the upper hand in the next century, unless stronger controls are instituted than any that are believed to be yet contemplated.

[And now we are told the UHI effect is insignificant!]

The World Meteorological Organization and The Footnote

[I really cannot finish this review without commenting on what is, quite frankly, an extraordinary footnote added at the end of the final chapter. It is typed in small print, just as any other notes. It says this, no more, no less :-

Since this chapter, (Approaches to the problem of forecasting), was written, however, an official statement, issued by the WMO in June 1976, places most emphasis on the prospects of man’s impact on the global climate, through the increasing production of CO2 and waste heat, both producing a warming effect expected to become dominant over the natural climate fluctuations by about 2000 AD.

The statement warned of dire consequences to be expected within the next 50-100 years through the displacement of the natural vegetation and crop belts and melting of ice caps.

Remember that Lamb could only have written this chapter a few months previously as he refers to the 1975 Schneider paper. So, despite all of the work put in by Lamb, despite the 24 studies, many commissioned by the WMO themselves. which attempted to predict the future, and despite the experience of the recent climatic record, the WMO suddenly decide to make global warming the overriding issue.

I say “suddenly” quite deliberately. If the WMO statement had been based on long and comprehensive deliberation, there would have been a wealth of empirical studies to back it up, which Lamb in turn would have considered before coming to his own judgment. It would also have been the case that Lamb would have commented on the WMO’s evolving position on the issue, and not add a short footnote just before publication.

It is hard to avoid the conclusion that the WMO statement was very much a “political” decision, rather than one based on the scientific evidence available at the time.]