How do scientists find evidence of climate change in the past?

Then scientists focus on climate from before the past 100-150 years, they use records from physical, chemical and biological materials preserved within the geologic record. Organisms (such as diatoms, forams and coral) can serve as useful climate proxies. Other proxies include ice cores, tree rings, and sediment cores.

Explanation:

To get at the data contained in ice cores, they must be melted so that the water from the outside of the core does not touch water from the center of the core

Explanation:

Scientists can also use ice cores to learn about the temperatures for each year. As snow accumulates onto a growing glacier, the temperature of the air imprints onto the water molecules in the ice.