From the article: "Drawing on a huge database of climate-recording objects from all over the world—including tree rings, cave formations, and ancient pollen tr

From the article: "Drawing on a huge database of climate-recording objects from all over the world—including tree rings, cave formations, and ancient pollen trapped in lake mud—the study concludes that 98 percent of Earth’s surface experienced its hottest period of the past 2,000 years within living memory. That uniform heat spike “is unprecedented over the Common Era,” it says." In other words, we have used a variety of scientific techniques to fill in the global climate data record.