Fig. 3: The permafrost area and its boundaries modelled for 18.9 °C of warming relative to present day, representative of the middle-late Tortonian (8.7 ± 0.4 Ma B.P.).
From: Arctic speleothems reveal nearly permafrost-free Northern Hemisphere in the late Miocene
A Areas sustaining discontinuous permafrost are marked by light purple (northern Greenland and Ellesmere Island). This is compared to present day permafrost extent (area marked by red, with darker reds representing higher amounts of soil organic carbon contained in the top 3 meters31). In the case of 23.4 °C warming (not mapped) these small areas of remaining discontinuous permafrost would disappear too, leaving the entire Northern Hemisphere permafrost-free. The caves with speleothem-based paleoclimate studies cited in the current research are shown by the blue rectangles. B The graph depicts soil organic carbon (SOC) vulnerable to thaw at a given mean annual air temperature (MAAT) increase (dark blue line) and the likely proportion33,34 of SOC released as carbon to the atmosphere within decades to centuries (light blue line), highlighting the Tortonian MAAT warming range (red dashed lines).
