evidence: Scientists often seek clues to past climates by drilling into glaciers and ice sheets. The extracted ice cylinders, sometimes taken from several kilometers below the surface, show evidence of atmospheric composition, volcanic eruptions, dust storms, even wind patterns. Combined with other paleoclimate records such as tree rings and fossils, ice cores enable scientists to reconstruct past worlds. [...] Paleoclimatology relies on ice cores but also tree rings, cores drilled from lake and ocean sediments, and fossils. Piecing together all the evidence produces a picture of a planet that was often much hotter than today, but was cooler than the present climate for most of the last 11,000 years. Ice cores also show that current carbon dioxide concentrations are now higher than they have been for hundreds of thousands of years, and the higher concentrations are driven by human burning of fossil fuels. Multiple paleoclimate records indicate cooler temperatures over the past 11,000 years, as shown in this cartoon. Credit: C. Iverson and E. Greenhalgh, NOAA Climate.gov, based on data from doi:10.1126/science.1228026