16 research outputs found
Pathways of ice-wedge degradation in polygonal tundra under different hydrological conditions
Ice-wedge polygons are common features of lowland tundra in the continuous
permafrost zone and prone to rapid degradation through melting of ground ice.
There are many interrelated processes involved in ice-wedge thermokarst and
it is a major challenge to quantify their influence on the stability of the
permafrost underlying the landscape. In this study we used a numerical
modelling approach to investigate the degradation of ice wedges with a focus
on the influence of hydrological conditions. Our study area was Samoylov
Island in the Lena River delta of northern Siberia, for which we had in situ
measurements to evaluate the model. The tailored version of the CryoGrid 3
land surface model was capable of simulating the changing microtopography of
polygonal tundra and also regarded lateral fluxes of heat, water, and snow.
We demonstrated that the approach is capable of simulating ice-wedge
degradation and the associated transition from a low-centred to a
high-centred polygonal microtopography. The model simulations showed
ice-wedge degradation under recent climatic conditions of the study area,
irrespective of hydrological conditions. However, we found that wetter
conditions lead to an earlier onset of degradation and cause more rapid
ground subsidence. We set our findings in correspondence to observed types of
ice-wedge polygons in the study area and hypothesized on remaining
discrepancies between modelled and observed ice-wedge thermokarst activity.
Our quantitative approach provides a valuable complement to previous, more
qualitative and conceptual, descriptions of the possible pathways of
ice-wedge polygon evolution. We concluded that our study is a blueprint for
investigating thermokarst landforms and marks a step forward in understanding
the complex interrelationships between various processes shaping ice-rich
permafrost landscapes.</p
Deciphering the imprint of topology on nonlinear dynamical network stability
Acknowledgments The authors gratefully acknowledge the support of BMBF, CoNDyNet, FK. 03SF0472A. The authors gratefully acknowledge the European Regional Development Fund (ERDF), the German Federal Ministry of Education and Research and the Land Brandenburg for supporting this project by providing resources on the high performance computer system at the Potsdam Institute for Climate Impact Research. The publication of this article was funded by the Open Access Fund of the Leibniz Association. We further thank Peng Ji for helpful discussions regarding the interpretation of the results.Peer reviewedPublisher PD
Thaw processes in ice-rich permafrost landscapes represented with laterally coupled tiles in a land surface model
Earth
system models (ESMs) are our primary tool for projecting future climate
change, but their ability to represent small-scale land surface processes is
currently limited. This is especially true for permafrost landscapes in which
melting of excess ground ice and subsequent subsidence affect lateral
processes which can substantially alter soil conditions and fluxes of heat,
water, and carbon to the atmosphere. Here we demonstrate that dynamically
changing microtopography and related lateral fluxes of snow, water, and heat
can be represented through a tiling approach suitable for implementation in
large-scale models, and we investigate which of these lateral processes are
important to reproduce observed landscape evolution. Combining existing
methods for representing excess ground ice, snow redistribution, and lateral
water and energy fluxes in two coupled tiles, we show that the model approach
can simulate observed degradation processes in two very different permafrost
landscapes. We are able to simulate the transition from low-centered to
high-centered polygons, when applied to polygonal tundra in the cold,
continuous permafrost zone, which results in (i) a more realistic
representation of soil conditions through drying of elevated features and
wetting of lowered features with related changes in energy fluxes, (ii)Â up to
2 ∘C reduced average permafrost temperatures in the current
(2000–2009) climate, (iii) delayed permafrost degradation in the future
RCP4.5 scenario by several decades, and (iv)Â more rapid degradation through
snow and soil water feedback mechanisms once subsidence starts. Applied to
peat plateaus in the sporadic permafrost zone, the same two-tile system can
represent an elevated peat plateau underlain by permafrost in a surrounding
permafrost-free fen and its degradation in the future following a moderate
warming scenario. These results demonstrate the importance of representing
lateral fluxes to realistically simulate both the current permafrost state
and its degradation trajectories as the climate continues to warm.
Implementing laterally coupled tiles in ESMs could improve the representation
of a range of permafrost processes, which is likely to impact the simulated
magnitude and timing of the permafrost–carbon feedback.</p
A 16-year record (2002–2017) of permafrost, active-layer, and meteorological conditions at the Samoylov Island Arctic permafrost research site, Lena River delta, northern Siberia: an opportunity to validate remote-sensing data and land surface, snow, and permafrost models
Most of the world's permafrost is located in the
Arctic, where its frozen organic carbon content makes it a potentially
important influence on the global climate system. The Arctic climate appears
to be changing more rapidly than the lower latitudes, but observational data
density in the region is low. Permafrost thaw and carbon release into the
atmosphere, as well as snow cover changes, are positive feedback mechanisms
that have the potential for climate warming. It is therefore particularly
important to understand the links between the energy balance, which can vary
rapidly over hourly to annual timescales, and permafrost conditions, which
changes slowly on decadal to centennial timescales. This requires long-term
observational data such as that available from the Samoylov research site in
northern Siberia, where meteorological parameters, energy balance, and
subsurface observations have been recorded since 1998. This paper presents
the temporal data set produced between 2002 and 2017, explaining the
instrumentation, calibration, processing, and data quality control.
Furthermore, we present a merged data set of the parameters, which were
measured from 1998 onwards. Additional data include a high-resolution digital
terrain model (DTM) obtained from terrestrial lidar laser scanning. Since the
data provide observations of temporally variable parameters that influence
energy fluxes between permafrost, active-layer soils, and the atmosphere
(such as snow depth and soil moisture content), they are suitable for
calibrating and quantifying the dynamics of permafrost as a component in
earth system models. The data also include soil properties beneath different
microtopographic features (a polygon centre, a rim, a slope, and a trough),
yielding much-needed information on landscape heterogeneity for use in land
surface modelling.
For the record from 1998 to 2017, the average mean annual air temperature
was −12.3 ∘C, with mean monthly temperature of the warmest month
(July) recorded as 9.5 ∘C and for the coldest month (February)
−32.7 ∘C. The average annual rainfall was 169 mm. The depth of
zero annual amplitude is at 20.75 m. At this depth, the temperature has
increased from −9.1 ∘C in 2006 to −7.7 ∘C in 2017.
The presented data are freely available through the PANGAEA
(https://doi.org/10.1594/PANGAEA.891142) and Zenodo
(https://zenodo.org/record/2223709, last access: 6 February 2019) websites.</p
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Chapter 1.2: Tipping points in the cryosphere
Drastic changes in our planet’s frozen landscapes have occurred over recent decades, from Arctic sea ice decline and thawing of permafrost soils to polar amplification, the retreat of glaciers and ice loss from the ice sheets. In this chapter, we assess multiple lines of evidence for tipping points in the cryosphere – encompassing the ice sheets on Greenland and Antarctica, sea ice, mountain glaciers and permafrost – based on recent observations, palaeorecords, numerical modelling and theoretical understanding.
With about 1.2°C of global warming compared to pre-industrial levels, we are getting dangerously close to the temperature thresholds of some major tipping points for the ice sheets of Greenland and West Antarctica. Crossing these would lock in unavoidable long-term global sea level rise of up to 10 metres. There is evidence for localised and regional tipping points for glaciers and permafrost and, while evidence for global-scale tipping dynamics in sea ice, glaciers and permafrost is limited, their decline will continue with unabated global warming.
Because of the long response times of these systems, some impacts of crossing potential tipping points will unfold over centuries to millennia. However, with the current trajectory of greenhouse gas (GHG) emissions and subsequent anthropogenic climate change, such largely irreversible changes might already have been triggered. These will cause far-reaching impacts for ecosystems and humans alike, threatening the livelihoods of millions of people, and will become more severe the further global warming progresses.
The scientific content of this chapter is based on the following manuscript in preparation: Winkelmann et al., (in prep
Global Tipping Points Report 2023: Ch1.2: Cryosphere tipping points.
Drastic changes in our planet’s frozen landscapes have occurred over recent decades, from Arctic sea ice decline and thawing of permafrost soils to polar amplification, the retreat of glaciers and ice loss from the ice sheets. In this chapter, we assess multiple lines of evidence for tipping points in the cryosphere – encompassing the ice sheets on Greenland and Antarctica, sea ice, mountain glaciers and permafrost – based on recent observations, palaeorecords, numerical modelling and theoretical understanding.
With about 1.2°C of global warming compared to pre-industrial levels, we are getting dangerously close to the temperature thresholds of some major tipping points for the ice sheets of Greenland and West Antarctica. Crossing these would lock in unavoidable long-term global sea level rise of up to 10 metres. There is evidence for localised and regional tipping points for glaciers and permafrost and, while evidence for global-scale tipping dynamics in sea ice, glaciers and permafrost is limited, their decline will continue with unabated global warming.
Because of the long response times of these systems, some impacts of crossing potential tipping points will unfold over centuries to millennia. However, with the current trajectory of greenhouse gas (GHG) emissions and subsequent anthropogenic climate change, such largely irreversible changes might already have been triggered. These will cause far-reaching impacts for ecosystems and humans alike, threatening the livelihoods of millions of people, and will become more severe the further global warming progresses
Heat stored in the Earth system 1960–2020: where does the energy go?
The Earth climate system is out of energy balance, and heat has
accumulated continuously over the past decades, warming the ocean, the land,
the cryosphere, and the atmosphere. According to the Sixth Assessment Report
by Working Group I of the Intergovernmental Panel on Climate Change,
this planetary warming over multiple decades is human-driven and results in
unprecedented and committed changes to the Earth system, with adverse
impacts for ecosystems and human systems. The Earth heat inventory provides
a measure of the Earth energy imbalance (EEI) and allows for quantifying
how much heat has accumulated in the Earth system, as well as where the heat is
stored. Here we show that the Earth system has continued to accumulate
heat, with 381±61 ZJ accumulated from 1971 to 2020. This is equivalent to a
heating rate (i.e., the EEI) of 0.48±0.1 W m−2. The majority,
about 89 %, of this heat is stored in the ocean, followed by about 6 %
on land, 1 % in the atmosphere, and about 4 % available for melting
the cryosphere. Over the most recent period (2006–2020), the EEI amounts to
0.76±0.2 W m−2. The Earth energy imbalance is the most
fundamental global climate indicator that the scientific community and the
public can use as the measure of how well the world is doing in the task of
bringing anthropogenic climate change under control. Moreover, this
indicator is highly complementary to other established ones like global mean
surface temperature as it represents a robust measure of the rate of climate
change and its future commitment. We call for an implementation of the
Earth energy imbalance into the Paris Agreement's Global Stocktake based on
best available science. The Earth heat inventory in this study, updated from
von Schuckmann et al. (2020), is underpinned by worldwide multidisciplinary
collaboration and demonstrates the critical importance of concerted
international efforts for climate change monitoring and community-based
recommendations and we also call for urgently needed actions for enabling
continuity, archiving, rescuing, and calibrating efforts to assure improved
and long-term monitoring capacity of the global climate observing system. The data for the Earth heat inventory are publicly available, and more details are provided in Table 4.</p
Sustainability, collapse and oscillations in a simple World-Earth model
The Anthropocene is characterized by close interdependencies between the natural Earth system and the global human society, posing novel challenges to model development. Here we present a conceptual model describing the long-term co-evolution of natural and socio-economic subsystems of Earth. While the climate is represented via a global carbon cycle, we use economic concepts to model socio-metabolic flows of biomass and fossil fuels between nature and society. A well-being-dependent parametrization of fertility and mortality governs human population dynamics. Our analysis focuses on assessing possible asymptotic states of the Earth system for a qualitative understanding of its complex dynamics rather than quantitative predictions. Low dimension and simple equations enable a parameter-space analysis allowing us to identify preconditions of several asymptotic states and hence fates of humanity and planet. These include a sustainable co-evolution of nature and society, a global collapse and everlasting oscillations. We consider different scenarios corresponding to different socio-cultural stages of human history. The necessity of accounting for the ‘human factor’ in Earth system models is highlighted by the finding that carbon stocks during the past centuries evolved opposing to what would ‘naturally’ be expected on a planet without humans. The intensity of biomass use and the contribution of ecosystem services to human well-being are found to be crucial determinants of the asymptotic state in a (pre-industrial) biomass-only scenario without capital accumulation. The capitalistic, fossil-based scenario reveals that trajectories with fundamentally different asymptotic states might still be almost indistinguishable during even a centuries-long transient phase. Given current human population levels, our study also supports the claim that besides reducing the global demand for energy, only the extensive use of renewable energies may pave the way into a sustainable future