Proxy data refers to measurements or indicators that provide indirect evidence of past conditions, such as climate or atmospheric conditions. Since direct measurements of past atmospheric conditions are often unavailable, scientists rely on proxy data to reconstruct historical climates. Examples of proxy data include tree rings, which can indicate growth conditions over time; ice cores, which trap air bubbles from different time periods; and sediment layers, which can provide information about past environmental conditions. Understanding proxy data is crucial for studying climate change and its impacts over long periods.