Reply on RC1

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Understanding the future evolution of permafrost requires a better understanding of its climatological past. This requires permafrost models to efficiently simulate the thermal dynamics of permafrost over the past centuries to millennia, taking into account highly uncertain soil and snow properties. In this study, we present a computationally efficient numerical permafrost model which satisfactorily reproduces the current thermal state of permafrost in the Arctic and its recent trend over the last decade. Also, the active layer dynamics and its trend is realistically captured. The performed simulations provide insights into the evolution of permafrost since the 18th century and show that permafrost on the North American continent is subject to early degradation, while permafrost on the Eurasian continent is relatively stable over the investigated 300-year period. Permafrost warming since industrialization has occurred primarily in three "hotspot" regions in northeastern Canada, northern Alaska, and, to a lesser extent, western Siberia. The extent of near-surface permafrost has changed substantially since the 18th century. In particular, loss of continuous permafrost has accelerated from low (&minus;0.10 &times; 10⁵ km² dec^&minus;1) to moderate (&minus;0.77 &times; 10⁵ km² dec^&minus;1) rates for the 18th and 19th centuries, respectively. In the 20th century, the loss rate nearly doubled (&minus;1.36 &times; 10⁵ km² dec^&minus;1), with the highest near-surface permafrost losses occurring in the last 50 years. Our simulations further indicate that climate disturbances due to large volcanic eruptions in the Northern Hemisphere, can only counteract near-surface permafrost loss for a relatively short period of a few decades. Despite some limitations, the presented model shows great potential for further investigation of the climatological past of permafrost, especially in conjunction with paleoclimate modeling.