A recent international collaboration led by Dr. GUO Donglin, a researcher at the Institute of Atmospheric Physics, Chinese Academy of Sciences, sheds light on the extent of near-surface (about 3–4 m depth) permafrost during the mid-Pliocene warm period (about 3.264–3.025 million years ago). This joint endeavor offers crucial historical references for understanding future permafrost change.
Permafrost, covering about a quarter of the Northern Hemisphere's land area, stores a large pool of ground ice and organic carbon. Permafrost is highly sensitive to climate change. Its degradation leads to melting of ground ice and release of organic carbon, triggering irreversible impacts on terrestrial ecosystems, surface hydrology, and engineering infrastructure.
Permafrost is thawing in the lower part of the Kolyma River in East Siberia (Image courtesy of Vladimir E. Romanovsky).
However, assessment of permafrost degradation effect remains challenging due to limited observations and large uncertainties in permafrost change projections. Some past warm periods have proxy data, which can be used to validate models and reduce simulation uncertainty. Consequently, these warm periods form a useful laboratory for studying potential future permafrost behavior and evaluating uncertainty of the projections.
By examining the mid-Pliocene warm period, the research reveals that near-surface permafrost was 93 ± 3% smaller than the preindustrial extent. Near-surface permafrost was present only in the eastern Siberian uplands, Canadian high Arctic Archipelago and northernmost Greenland. The simulations are similar to near-surface permafrost changes projected for the end of this century under the SSP5-8.5 scenario.
"This study provides a geological basis for understanding the future changes in near-surface permafrost. It indicates that during the mid-Pliocene warm period, which shares characteristics of the projected future climate, near-surface permafrost extent was highly constrained. This will come with critical implications for understanding permafrost change and associated climate, ecological, and societal impacts in our warming world", stated by Dr. GUO.
The study is published in the journal
Proceedings of the National Academy of Sciences (PNAS) under the title "Highly restricted near-surface permafrost extent during the mid-Pliocene warm period". Dr. Donglin Guo serves as both the first author and corresponding author of the paper.
