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

Regional principal components for temperature and precipitation PNAS

Geospatial-temporal analysis reveals two trends in global climate during the last deglaciation

The last deglaciation was characterized by increases in surface temperatures of 10-15 °C punctuated by millennial-scale warming/cooling periods, pulses of increasing atmospheric carbon dioxide and asynchronously increasing methane. A geospatial-temporal variance analysis reveals a global warming trend correlating with rising CO2 on which is superimposed second trend millennial-scale regional warming/cooling periods associated with variation in the strength of the Atlantic overturning current.

Global surface temperature reconstruction reveals cooling preceded shift to 100,000-year glacial/deglacial cycles 800,000 years ago

In this study the global average surface temperature over the past 2 million years has been derived from deep sea cores. The results reveal that global cooling occurred about 300,000 years before the rapid ice sheet growth and the development of the first 100,000-year glacial/deglacial cycle about 800,000 years ago.

Evidence of biological feedback driving warming at ice age terminations

It is known that orbital forcing is involved in glacial/deglacial cycles but is insufficient by itself to explain the glacial/deglacial cycles. This study argues that a biological feedback mechanism kicks in when a threshold is reached and together with orbital forcing results in the sustained and rapidly increasing CO2 and surface temperature of a deglaciation.

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.