Warm/cool epochs over past 2000 years were regional until 20th century warming

Percentages of earth’s surface experiencing abnormal warm (red shading) and cold (blue shading) temperatures. Shading intensity indicates the magnitude of warmth and cold. a, Annual data. b, 51-year averaged data.

Over the last 2000 years Europe has experienced centennial scale cool and warm epochs including the Little Ice Age (1300 and 1850 CE), the Mediaeval Warm Period (800–1200 CE), the Dark Ages Cold Period (400–800 CE) and the Roman Warm Period (250 BCE to 400 CE). A recent analysis has generated spatial temporal temperature reconstructions covering the entire globe for the past 2,000 years. The research found no evidence that preindustrial cold and warm periods recorded in Europe and elsewhere extended over the entire globe. By contrast, the warmest period of the past 2,000 years occurred during the twentieth century for more than 98 per cent of the globe.

No evidence for globally coherent warm and cold periods over the preindustrial Common Era, Raphael Neukom, Nathan Steiger, Juan José Gómez-Navarro, Jianghao Wang & Johannes P. Werner, Nature, volume 571, pages 550–554 (2019).

From Our Files

Greenland ice cores reveal warming of 10 °C in three years

High-resolution Greenland ice core records reveal two warming events at the end of the last ice age involved warming of more than 10 °C. Furthermore the warming transition beginning 14,700 years ago occurred within only three years.

Accelerating ocean warming revealed by extensive oceanic buoy network

Improved data coverage and analysis has made it possible to reconstruct temperature profiles across most ocean basins and at all depths to 6000 meters (m) from 1960 to 2015. The reconstructions reveal accelerating heating in the upper layers above 2000 m. Ocean warming is stronger since the late 1980s compared to the 1960s to the 1980s.

Location of core site on the Bermuda Rise

Changes in Atlantic current triggered abrupt Northern hemisphere warming events during last ice age

This study reports measurements from ocean floor sediments that provide the first direct evidence that not only do variations in the primary North/South Atlantic current correlate with periods of rapid warming and slower cooling in the Northern Hemisphere during the last ice age, but that the changes in the Atlantic overturning current occurred before and likely initiated these warming/cooling cycles.

Evidence of CO2 outgassing from the Southern Ocean early in the last deglaciation

During the last deglaciation atmosphere CO2 concentration rose by about 80 ppm amplifying climate warming. This study of radiocarbon in deep sea corals found that Southern ocean deep water was radiocarbon-depleted throughout the last ice age, but this depletion disappeared between 16,600 and 14,600 years ago consistent with Southern Ocean CO2 outgassing that corresponded to the first pulse of increased atmospheric CO2 early in the deglaciation.