Page:On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground.pdf/30

By means of these values, I have calculated the mean alteration of temperature that would follow if the quantity of carbonic acid varied from its present mean value (${\text{K}}=1$) to another, viz. to ${\text{K}}=0.67$, $1.5$, $2$, $2.5$, and $3$ respectively. This calculation is made for every tenth parallel, and separately for the four seasons of the year. The variation is given in Table VII.

A glance at this Table shows that the influence is nearly the same over the whole earth. The influence has a minimum near the equator, and increases from this to a flat maximum that lies the further from the equator the higher the quantity of carbonic acid in the air. For ${\text{K}}=0.67$ the maximum effect lies about the 40th parallel, for ${\text{K}}=1.5$ on the 50th, for ${\text{K}}=2$ on the 60th, and for higher ${\text{K}}$-values above the 70th parallel. The influence is in general greater in the winter than in the summer, except in the ease of the parts that lie between the maximum and the pole. The influence will also be greater the higher the value of $\nu$, that is in general somewhat greater for land than for ocean. On account of the nebulosity of the Southern hemisphere, the effect will be less there than in the Northern hemisphere. An increase in the quantity of carbonic acid will of course diminish the difference in temperature between day and night. A very important secondary elevation of the effect will be produced in those places that alter their albedo by the extension or regression of the snow-covering (see p. 257), and this secondary effect will probably remove the maximum effect from lower parallels to the neighbourhood of the poles^[1].

It must be remembered that the above calculations are found by interpolation from Langley's numbers for the values ${\text{K}}=0.67$ and ${\text{K}}=1.5$, and that the other numbers must be regarded as extrapolated. The use of Pouillet's formula makes the values for ${\text{K}}=0.67$ probably a little too small, those for ${\text{K}}=1.5$ a little too great. This is also without doubt the case for the extrapolated values, which correspond to higher values of ${\text{K}}$.

We may now inquire how great must the variation of the carbonic acid in the atmosphere be to cause a given change of the temperature. The answer may be found by interpolation in Table VII. To facilitate such an inquiry, we may make a simple observation. If the quantity of carbonic acid decreases from $1$ to $0.67$, the fall of temperature is nearly the same as the increase of temperature if this quantity augments to $1.5$. And to get a new increase of this order of magnitude (3°.4), it will be necessary to alter the quantity of carbonic acid till it reaches a value nearly midway between $2$ and $2.5$.

1. See Addendum, p. 275.