The <scp>L</scp>ast <scp>P</scp>ermafrost <scp>M</scp>aximum (<scp>LPM</scp>) map of the <scp>N</scp>orthern <scp>H</scp>emisphere: permafrost extent and mean annual air temperatures, 25–17 ka <scp>BP</scp>

Abstract

This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice‐wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo‐temperatures that are inferred on the basis of present‐day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately &lt;1000 m a.s.l.). Striking features that appear from the map are (i) the narrow permafrost zone in N orth A merica, which contrasts with the broader LPM permafrost zone in E urasia (that may be related to different snow thickness or vegetation cover), (ii) the zonal extent of former LPM permafrost (that may reflect sea‐ice distribution), which contrasts with the present‐day pattern of permafrost extent (especially in E urasia) and (iii) the relatively narrow zones of LPM discontinuous permafrost (that may indicate strong temperature gradients).