During the Pliocene epoch (5.3 to 2.6 million years ago) climate became cooler and drier, and seasonal, similar to modern climates. The global average temperature in the mid-Pliocene was 2–3 °C higher than today, global sea level 80 feet higher and the northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 million years ago. Scientists are looking at what climate conditions were like 3.3 to 3 million years ago, during a geologic period known as the Pliocene, and they are confident in the accuracy of their data. The Pliocene is the most recent period of sustained global warmth similar to what is projected for the 21st century. Climate during this time period offers one of the closest analogs to estimate future climate conditions.