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Titel |
Threshold driven response of permafrost in Northern Eurasia to climate and environmental change: from conceptual model to quantitative assessment |
VerfasserIn |
Oleg Anisimov, Vasiliy Kokorev, Svetlana Reneva, Nikolai Shiklomanov |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250032990
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Zusammenfassung |
Numerous efforts have been made to access the environmental impacts of changing climate in
permafrost regions using mathematical models. Despite the significant improvements in
representation of individual sub-systems, such as permafrost, vegetation, snow and
hydrology, even the most comprehensive models do not replicate the coupled non-linear
interactions between them that lead to threshold-driven changes. Observations indicate
that ecosystems may change dramatically, rapidly, and often irreversibly, reaching
fundamentally different state once they pass a critical threshold. The key to understanding
permafrost threshold phenomena is interaction with other environmental factors that
are very likely to change in response to climate warming. One of such factors is
vegetation.
Vegetation control over the thermal state of underlying ground is two-fold. Firstly,
canopies have different albedo that affects the radiation balance at the soil surface. Secondly,
depending on biome composition vegetation canopy may have different thermal conductivity
that governs the heat fluxes between soil and atmosphere. There are clear indications based
on ground observations and remote sensing that vegetation has already been changed in
response to climatic warming, in consensus with the results of manipulations at
experimental plots that involve artificial warming and CO2 fertilization. Under
sustained warming lower vegetation (mosses, lichens) is gradually replaced by
shrubs. Mosses have high thermal insolating effect in summer, which is why their
retreat enhances permafrost warming. Taller shrubs accumulate snow that further
warms permafrost in winter. Permafrost remains unchanged as long as responding
vegetation intercepts and mitigates the climate change signal. Beyond certain threshold
enhanced abundance and growth of taller vegetation leads to abrupt permafrost
changes.
Changes in hydrology, i.e. soil wetting or drying, may have similar effect on permafrost.
Wetting increases soil thermal conductivity and leads to enhanced active-layer thickness, soil
depression, and ponding. Above certain threshold the process becomes self-sustained
ultimately leading to degradation of permafrost.
Threshold mechanisms are intrinsically probabilistic, and new type of permafrost
model has been developed to address them. Unlike conventional models, it takes
into account the small-scale spatial variability of soil, snow, and biophysiographic
parameters in the calculations of the statistical ensemble representing potential states of
permafrost under the prescribed conditions. Such model was used to assess changes in
permafrost in Northern Eurasia under current and projected for the future climatic
conditions.
Results indicate that 1–2Ë C warming will lead to large-scale degradation of the
frozen ground in the southernmost zone of sporadic permafrost. In continuous and
discontinuous zones patchy effects will be manifested in vegetation changes at individual
locations and subsequent local retreat of permafrost. Under sustained warming
such changes will affect larger areas ultimately changing the landscape while local
biophysiographic factors, i.e. soil, topography, slope, etc., will still play important role.
Warming by more than 2Ë C may lead to completely different vegetation patterns in the
entire Arctic, with new biomes and taller and more productive spices replacing
typical plant forms. Together with the direct warming effect it will make existence of
near-surface permafrost virtually impossible in the modern sporadic and large part of the
discontinuous zones, although at larger depths relict frozen ground will remain for
centuries.
Support for this research comes from the Russian foundation for basic research (project
09-05-13544), Otto-Schmidt polar research laboratory (project OSL-10-02), and NASA
(project NNX08AP30G). |
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