Correlations and causal relationships between historical climatic indicators and price data

In order to generate coefficients by which air temperatures in the past may be estimated from price data, Libby ( 1977) relates changes ill the price of wheat, and in the wheat equivalents of wages, to instrumentally recorded air temperatures.   However, the crucial effects on prices of changes in the population (and of demand generally) are neglected; the allowance made for the changing value of money ill terms of wheat is inadequate; and the suggested relationship between air temperatures and grain prices is not evident in the long term.    Accordingly, the validity of temperature scales derived from correlations  Bengal be accepted.