evidence: In order to fully understand the implications of how climate is changing today, it is important to look at historical records to see how climate has changed in the past. Current climate data collection methods, including satellite observations, only cover a very small window of Earth's long history with respect to climate change time scales. Luckily, clues to past climatic conditions, dating hundreds of thousands of years back in time, are recorded in glacial ice all over the world. Paleoclimatologists (scientists who study past climate) make inferences based on indirect measures of proxy dataproxy data: data that paleoclimatologists gather from natural recorders of climate variability, e.g., tree rings, ice cores, fossil pollen, ocean sediments, coral and historical data, that can help extend our understanding of climate far beyond the 140 year instrumental record.biological, geological, or chemical indicators that reflect climate conditions. For example, glacial ice is made up of layer upon layer of compacted snowfall that contains dust, pollen, gas bubbles, and other materials that give us clues about what climate was like at different times in the past.