certain_people t1_ja5zi0n wrote

The dating doesn't give you the gas levels or temperatures.

Instead separate samples are taken through an ice core, or a sediment core, or a rock sequence. Separate analyses are done on the samples to measure the greenhouse gas levels, temperatures, and ages.

Sediment samples might have carbon isotopes measured as a proxy for CO2, ice cores might have gas bubbles analysed, there's a whole suite of different measurements possible. The dating is totally separate and just puts some age pins on those measurements.


certain_people t1_j53855q wrote

Global average was that much cooler. Not everywhere cools by the same amount. The further away from the equator, approximately, the more intense the cooling.

Same thing in reverse now. Global average up 1°C since 1880, but parts of the Arctic are over 4°C warmer.