What was the Mid-Holocene Climatic Optimum?

The Mid-Holocene Climatic Optimum refers to a period roughly 5,000 to 7,000 years ago when many parts of the globe experienced relatively warm conditions. Because of this warmth, the interval is sometimes called the Climatic Optimum or, in North America, the "Altithermal" or "Xerothermic Interval".12

It is important to note that this was not a uniform global event. While some regions and seasons were warmer than today, others experienced cooler conditions. Recent climate models suggest that global mean temperatures during this time were likely 0.2–0.3 °C (0.4–0.5 °F) colder than late 20th-century averages. The warmth was primarily driven by orbital variations that altered the seasonal and latitudinal distribution of solar radiation, favoring warmer summers at higher latitudes in the Northern Hemisphere.12

Regional records show significant heterogeneity in both temperature and moisture, as changing patterns of atmospheric circulation and ocean currents caused different areas to reach their thermal maximum at different times.2