How does scientists use ice to study ancient climates

To look for clue about the Earth's environment, paleoclimatologists (scientists that study the acient climates), they usually study many natural environment like the bottom of the ocean, trees' rings or ice caps (and glaciers). Many of these have some types of bands, rings and layers that can vary from in thickness, colour, chemical composition, and many more, allowing scientists to know more about the climate at the time each layer form.