well the answer is through ice cores and pollen grains
Scientists can drill deep into the ice to collect ice cores. Pollen grains on ice help make inferences about the climatic area. Scientists can study tree rings on ice to learn more about past climates.
The oxygen in the water particles also endures a code to the former environment. Investigators can apply the oxygen particles in the polar glacier as a substitute for air temperature beyond the iceberg.
Ice layers on the landmasses have developed and then withdrawn repeatedly four times in the preceding half million years.
