The Holocene Thermal Maximum, an Ancestor of Modern Climate Change

Meltwater runoff from the Greenland icesheet is a foreboding sight

Records from Greenland lakes show rapid deglaciation during a Holocene warm period, highly reflective of minimum future projections.

The Holocene Thermal Maximum (HTM) was a recent warm period that occurred 9-5 kya Before Present (BP), as a result of orbital forcing. During the HTM, it is suggested that temperatures in the arctic rose 2-4 °C in response, causing minimal local sea level rise of 0.16 m. The Intergovernmental Panel on Climate Change (IPCC) predict that the global mean temperature will rise 2-7 °C by 2100 CE if pCO2 emissions continue at their current rate, suggesting that these results are only showing the lowest end of the climate change spectrum.

Researchers from Universities in Denmark, Canada, and Belgium, took cores of threshold lake sediments in southern Greenland. When the icesheet was close to the lakes, sediments were dominant in meltwater clays, however a change to black peats – reminiscent of organic material – was suggestive of deglaciation. When fed into a model, the results showed a whopping 20-60 km retreat of the ice margins behind their present positions.

Ancient warming events are our best insight into climate change, but the circumstances, however similar, are also not completely interchangeable considering that CO2 has never been unleashed in such a quantity (increases of 2.66ppm/yr) on the timescales we are seeing presently.

A close contender was the mid-Pliocene Thermal Maximum (mPTM) 3.264-3.025 Ma, in which pCO2 concentrations were 350-400 ppm  – a 30% higher value than pre-industrial Holocene, and a value we are rapidly approaching. The interval was marked with minimal ice cover, resulting in biblically high seas 5-40 m higher than today; an utterly terrifying prospect in this day and age.

Eventhough Man is changing the planet in ways never changed before, ancient analogues can at least give us a reliable glimpse into what’s to come. It would seem that at present, even if the deepest contents of Pandora’s box are still a mystery, at least now we may have an idea what could emerge from it first.


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Martine Coates

Marketing Executive at Scarab4
Geologist hailing from the University of Southampton with a specialism in marine volcanic sedimentology and the subaqueous emplacement of subaerial volcanic mass flows. Now working for the LLW Repository Ltd in Cumbria, UK as part of the Environmental Monitoring and Site Characterisation team.

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