ENVIRONMENT

The Eemian, the Last Interglacial

~130,000 to 115,000 years ago

Palaeolithic · Middle Stone Age · Eemian

The Eemian is the warm interval that separated the two most recent glaciations, known in marine records as isotope stage 5e and placed by convention between about 130,000 and 116,000 years ago. Across the globe the warmth was modest: a network of sea-surface temperature records puts the peak annual mean about 0.5 degrees C above the 1870 to 1889 average, a value indistinguishable from the 1995 to 2014 one. High latitudes were another matter, running some 3 to 5 degrees C warmer than today, and that is where the difference told. Raised coral shorelines dated by uranium and thorium put global sea level 5.5 to 9 metres above the present one, which requires ice sheets smaller than today's in both Greenland and Antarctica. On land, mixed forests took hold across Europe from about 127,000 years ago, and open vegetation replaced them in the northwest after about 115,000.

Why it matters

The interval offers the most recent natural analogue for a world slightly warmer than the pre-industrial one, and its lesson lies in the gap between a small temperature signal and a large marine response. Half a degree of global warmth, concentrated at high latitudes, went with shorelines several metres above the present ones. The authors of the sea-level reconstructions draw the same conclusion from it: ice sheets answer to small changes in radiative forcing, and stay vulnerable over the long term to warming that is moderate but sustained.

Dating & uncertainty

Both ends are conventions as much as measurements. Marine isotope stage 5e is dated by correlation with uranium and thorium ages on raised coral reefs, and set by convention between about 130,000 and 116,000 years, whereas European pollen sequences place the Eemian forests later, from about 127,000 to 115,000. The sea-level figure has its own spread: 5.5 to 9 metres above present from coral shorelines, or at least 6.6 metres with 95 per cent probability from a statistical model. What the spread moves is the share credited to each ice sheet, not the finding that both were smaller than today.

Sources

1. Dutton & Lambeck (2012), Science · Ice Volume and Sea Level During the Last Interglacialdoi:10.1126/science.1205749
2. Kopp et al. (2009), Nature · Probabilistic assessment of sea level during the last interglacial stagedoi:10.1038/nature08686
3. Hoffman et al. (2017), Science · Regional and global sea-surface temperatures during the last interglaciationdoi:10.1126/science.aai8464
4. Kukla et al. (2002), Quaternary Research · Last Interglacial Climatesdoi:10.1006/qres.2001.2316

Our species’ history as one day

14:05:429 h 54 min before midnight

if the 315,000 years of Homo sapiens were compressed into a single day