Neither did we consider the thinning of ice layers as the tremendous weight above forces the ice at lower levels to squeeze out horizontally. In round figures say, to the nearest 10, yearshow far back can you use separate layers to date an ice core? I would say it's obvious that covering large areas of the Earth with concrete, asphalt, and metal and uncovering large areas and leaving them as wet dirt would cause a lower albedo quite a bit. The simplest reason that it works this way is that cold water does not evaporate very much. In addition, thermal drills are typically bulky and can be impractical to use in areas where there are logistical difficulties.
Check what others have done first if you think it can done with albedo in NH only.
How are ice cores dated?
Reconstructing Climates of the Quaternary. Johnsen, S. This Image produced by NOAA show the near orentiation of the earths axis about 3, years ago, when the earths axis was located at the 45 Degrees North mark. Since ice cores are a measure of the water in the ice, what the ice core is actually measuring are the conditions of the oceans that the water originally evaporated from. The New Yorker.