The title above is one that Joe Jennings used in 1981 for a paper at the Eighth International Congress of Speleology. What is surprising is that it got past an American editor! However, the Shakespeare part probably helped.

Dean Smart, who is an ACKMA member and a Cave Management Consultant with the Royal Forest Department in Thailand, recently sent me an email in which he suggested some ANDYSEZ topics - such suggestions are few and far between - thanks Dean. The first matter he raised is as follows:

How significant is temperature for formation of caves and karst? Bearing in mind that temperature inversely affects CaC03 saturation point, temperature also decreases the Reynolds Number limit of Darcy's Law and therefore laminar flow becomes turbulent flow earlier. Higher tropical temperatures may allow more rapid speleogenesis and explain the abundance of caves found here (do you think?). Is temperature alone this significant? Obviously many other factors are involved. Higher rainfall and lack of glaciation may explain although soil CO2 measurements are similar to temperate zones.

Wow! Lots of chemistry, physics and geomorphology in that lot - and has been one of the enduring debates in geomorphology - especially karst geomorphology - for many decades. Does climate determine the ultimate landform or can we get similar landforms under different climatic regimes? Predictably the answer is probably yes - and no. To quote Joe:

The role of climate in karst style ...has been simplistically exaggerated by many, including the author. Nevertheless it is conceived as more than minor despite obscurity cast by complex interactions of structure, process and time, and by uncertainty whether time and process intensity compensate for one another.

So now we have a few more factors to consider. We assume that we have water available - can't do much without it and we need to simplify something. What does increasing temperature do?

• chemical reactions speed up
• water can hold less CO2 - so all other things being equal it will be less aggressive
• biological activity increases so more CO2 is available from respiration and decay to make water more aggressive
• the viscosity of water decreases so that it can become turbulent in smaller spaces
• and a lot of other factors.

Note that some of these work against one another. The results can be summed up in the following diagram:

Figure 1. Schematic diagram based on Jennings (1985) and Atkinson and Smith (1976) showing the relationship between increasing runoff and limestone solution as shown by the regression line. The ellipses show the results of observations in different broad climatic regimes. It is apparent that the influence of increased runoff exerts a stronger influence than "temperature" as expressed by broad climatic zones. See text for further discussion. Jane Gough prepared the figure.

The figure is schematic but based on the experiments and observations of a large number of studies with a wide variety of experimental and other errors. However, a regression (relationship) line can be drawn using all the results which shows that more runoff results in more limestone solution. Surprise! Surprise! I hear you cry - but wait a minute. Seems obvious.

By the way, we are using runoff rather than rainfall because runoff is a measure of effective rainfall. That is, rainfall that does work (dissolves things in this case) rather than just evaporates or sits around as ice and snow.

The straight line shows the form of the relationship. The ellipses enclose the results of the various studies - if they were just dots on a scatter diagram we would not be able to say very much. However, I know how the dots are distributed and they fall into three sort-of broad climatic groups that I have included in the ellipses. There are exceptions and departures but broadly the picture is as you see it. Lets have some explanations:

• Runoff and limestone removal in the arctic/alpine ranges from virtually nothing to more than anywhere else. This can be explained by the fact that at one end there is not much runoff because the water is locked up in ice and snow - at the other by mountains collecting lots of rainfall which runs off and dissolves the limestone.
• A trend line through the "tropics" ellipse is. steeper than the generalised trend and that for the arctic/alpine and the mid-latitude. More limestone is being removed for a given level of runoff and the answer probably lies in higher temperatures speeding up the kinetics of the reactions and more biological activity providing more carbon dioxide.
• The mid-latitudes are intermediate but have a larger data scatter perhaps reflecting the influence of other factors on the limestone solution conundrum - if I showed you the original data you would see that there is a preponderance of data points toward the left and down reinforcing the idea that these areas are less eroded than the arctic/alpine and tropical areas - and that is roughly what we see when we look globally at the degree of karstification.

In the words of the immortal Dr Julius Sumner-Miller (apologies to my younger readers - perhaps they will remember the glass and a half of milk?) "why is it so?".

Willy White (White 1984) has looked at the heavy theoretical chemistry side of the water - carbon dioxide - limestone system and has found (according to Jennings 1985, p 194) the kinetics agree with the "dominating linear relationship between denudation and runoff".

Temperature which affects reaction rates, viscosity and so on only increases solution rates by about 30% from 5°C to 25°C. Raising carbon dioxide levels only increase solution rates as a cube root of the level of carbon dioxide so enhanced solution rates from this source increase only slowly with the gains to be expected from this source. Ford and Williams (1989, p97) say:

For a given runoff, it appears to involve an increase not of ten times between the tropics and the cool temperate alpine zones, but only 36%. The greatest limestone solution in the world occurs where it is wettest. Hence precipitation rather than temperature is the principal control.

As a result temperature increases do not enhance limestone removal as much as increased water availability does. And there you have it!

But, don't go yet! There a heap of other factors involved in the degree of karstification. Let's identify some:

• time available for rain to work on the rock
• inherited landforms
• hydrological considerations (is there a high degree of runoff from non-limestone terrains?)
• the fabric, structure and chemical makeup of the rock mass
• and probably other things.

Ford and Williams (1989, p 466) say:

Most geomorphologists now agree that broad landscape differences exist in regions with contrasting climates, while admitting that subtler variations in style has often been claimed than objective scrutiny can justify. A more important criticism of climatic geomorphology is that it has been unable to explain why many of these contrasts occur. For example, it has not been revealed why karstic activity in the humid tropics sometimes results in the development of cockpit karst, whereas the temperate zone doline karst is apparently more typical - even though dolines are found in the tropics. It appears to us that climato-genetic geomorphology has reached about the limit of its contribution. We should now pass on, but avoid the mistake of failing to recognise the value of its major conclusions.

Or, as Joe put it in 1981, lets not "throw the baby out with the bathwater". Hope this helps, Dean.

REFERENCES

Atkinson TC and Smith DI 1976 The Erosion of Limestones, pp 151-177 in The Science of Speleology (ed. TD Ford and CHD Cullingford), Academic Press, London.

Ford DC and Williams PW 1989 Karst Geomorphology and Hydrology, Unwin Hyman, London.

Jennings JN 1981 Morphoclimatic control - a tale of piss and wind or the baby out with the bathwater?, Proceedings of the Eighth International Congress of Speleology, Volume 1, 367368.

Jennings JN 1985 Karst Geomorphology, Basil Blackwell, Oxford.

White WB 1984 Rate processes: Chemical kinetics and karst landform development, pp 227-248 in Groundwater as a Geomorphic Agent (ed. RG LaFleur), Allen and Unwin, London.