Mid-Holocene Warmth and Temperature Trends: Reconstructing Holocene Climate using a Global Proxy Database and Five Statistical Methods

Abstract:

The Holocene represents an important period for quantifying long-term temperature variability and trends in a climate similar to the modern day. Here we explore a newly compiled database of temperature-sensitive proxy records from 679 sites around the globe, consisting primarily of lake sediments, marine sediments, peat, and ice. This proxy record database, called Temperature 12k, is the basis for a multi-method temperature reconstruction of global to sub-hemispheric temperatures over the past 12,000 years. Different methods—such as composite-plus-scale and pairwise comparison—utilize different approaches to age and calibration uncertainties, and are used to reconstruct and quantify Holocene temperature variability on multi-century and millennial timescales. Results show a period of mid-Holocene warmth centered around 6,500 years ago with temperatures approximately 0.7°C higher than the 19th Century, followed by a gradual cooling to the Little Ice Age. Temperature trends in different latitude bands suggest larger temperature anomalies in the Northern Hemisphere than the Southern Hemisphere. The five reconstruction methods show some uncertainty in the magnitude of changes but are generally similar in many aspects of Holocene climate variability.

Seasonal biases, calibration uncertainties, and spatial distribution of proxy records remain areas for potential improvement, and future reconstruction efforts must explore these topics in more depth. However, the assembled proxy database represents an important resource for Holocene exploration, and these initial temperature reconstructions allow us to better quantify peak Holocene warmth, latitudinal changes, and multi-centennial to millennial-scale climate variability during this important period of Earth’s past.