An anonymous reader quotes a report from Phys.Org: A University of Arizona-led effort to reconstruct Earth’s climate since the last ice age, about 24,000 years ago, highlights the main drivers of climate change and how far out of bounds human activity has pushed the climate system. The study, published this week in Nature, had three main findings:

1.) It verified that the main drivers of climate change since the last ice age are rising greenhouse gas concentrations and the retreat of the ice sheets.
2.) 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.
3.) The magnitude and rate warming over the last 150 years far surpasses the magnitude and rate of changes over the last 24,000 years.

There are different methods for reconstructing past temperatures. The team combined two independent datasets — temperature data from marine sediments and computer simulations of climate — to create a more complete picture of the past. 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. Computer-simulated climate models, on the other hand, provide temperature information based on scientists’ best understanding of the physics of the climate system, which also isn’t perfect. The team decided to combine the methods to harness the strengths of each. This is called data assimilation and is also commonly used in weather forecasting. […] Now, the team is working on using their method to investigate climate changes even farther in the past.