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Let me make it clear what an ice sample is. The samples researches collect by drilling deep inside the polar ice sheets in Greenland,Antarctica as well as some high mountain ice caps and glaciers are known as ice cores. There are two parts to the question let me handle them one at a time.
1. What can the ice tell us about past climates?
Ice sheets and glaciers near Earth's North and South poles form from years of accumulating snowfall. The weight from each years snowfall compresses down the previous layers of snow creating massive snow fields. As snow deposits onto a growing glacier, the temperature of the aiir imprints onto the water molecules. They also hold tiny particles of aerosols as dust, ash pollen, trace elements and sea salts that were present in the atmosphere at that time. These are preserved so in the ice for thousands of years later, providing physical evidence of past global events, such as major volcanic eruptions.
Similarly the gases in the atmosphere including green house gases like carbon-dioxide and methane are packed in the snow as tiny bubbles. These 'fossil' air bubbles provide evidence of what the atmosphere was like when that layer of ice formed, and about the paleoclimate.
2. How do ice cores help make predictions about future climate change?
Ice core temperature data are used to validate climate models that predict Earth's future climate. Scientists build all the existing knowledge about how the atmosphere, ocean, land and ice work. They also have to add in any variables that may alter the climate system at different points in time-such as earth's location in its orbit and how far it will be from the sun.
Carbon and dust content are the most important indicators that directly indicate the climate in any given time period. Through the analysis of carbon isotopes in particular and the rest of the radioisotopes of certain chemical elements, the corresponding climatic characteristics can be estimated for a specific period of time. The presence of certain elements and minerals is a direct indicator of a climatic state Specific.
By studying the geochemistry of ancient glaciers and their geochemical content, general climatic characteristics can be identified in that era. By determining the climate in successive periods, the general cycle of climate is determined and thus models can be developed that simulate future climate and predict future climate scenarios
