UNDERGROUND RECORDS OF CHANGING CLIMATE

Scientists believe that past climate can be inferred from borehole temperatures. The theory is that temperature at the surface is conducted down to depth, albeit with a certain lag time. As surface temperature oscillations propagate downwards they become smaller and die out. Diurnal temperature variations only penetrate to about a metre, while century long signals can reach a depth of 150m, and millennia scale signals to 500m. To read the signal, the effect of outward going heat from the earth's core must be isolated. -R.Gower