How do scientists use ice to study ancient climates

Counting the yearly layers can date them. The oxygen in the water molecules also holds a key to past climate. Scientists are able to use the oxygen atoms in the glacial ice as a proxy for air temperature above the glacier.

Answer: Ice is very important for studying ancient climates. Ice can preserve the remains of organisms such as a Wholly Mammoth, possibly for hundreds of thousands of years. The details and phenotype of the mammoth such as its fur, can provide evidence of Earth's ancient climate, and where it occurred (which is somewhere that contains ice).