evidence: - It suggests a general warming trend over the last 10,000 years, settling a decade-long debate about whether this period trended warmer or cooler in the paleoclimatology community. [...] The researchers looked at the chemical signatures of marine sediments to get information about past temperatures. Because temperature changes over time can affect the chemistry of a long-dead animal's shell, paleoclimatologists can use those measurements to estimate temperature in an area. It's not a perfect thermometer, but it's a starting point.