scholarly journals Hypersensitivity of glacial temperatures in Siberia

2019 ◽  
Author(s):  
Pepijn Bakker ◽  
Irina Rogozhina ◽  
Ute Merkel ◽  
Matthias Prange
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Cold Climate ◽  
Ice Age ◽  
Geological Evidence ◽  
Model Experiments ◽  
Summer Temperatures ◽  
Glacial Periods

Abstract. Climate change in Siberia is currently receiving a lot of attention as large permafrost-covered areas could provide a strong positive feedback to global warming through the release of carbon that has been sequestered there on glacial-interglacial time scales. Geological evidence and climate model experiments show that the Siberian region also played an exceptional role during glacial periods. The region that is currently known for its harsh cold climate did not experience major glaciations during the last ice age, including its severest stages around the Last Glacial Maximum (LGM). On the contrary, it is thought that glacial summer temperatures were comparable to present-day. We combine LGM experiments from the second and third phases of the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) with sensitivity experiments with the Community Earth System Model (CESM). Together these climate model experiments reveal that the intermodel spread in LGM summer temperatures in Siberia is much larger than in any other region of the globe and suggest that temperatures in Siberia are highly susceptible to changes in the imposed glacial boundary conditions, the included feedbacks and processes, and to the model physics of the different components of the climate model. We find that changes in the large-scale atmospheric stationary wave pattern and associated northward heat transport drive strong local snow and vegetation feedbacks and that this combination explains the susceptibility of LGM summer temperatures in Siberia. This suggests that a small difference between two glacial periods in terms of climate, ice buildup or their respective evolution towards maximum glacial conditions, can lead to strongly divergent summer temperatures in Siberia, that are sufficiently strong to allow for the buildup of an ice sheet during some glacial periods, while during others, above-freezing summer temperatures will preclude a multi-year snow-pack from forming.

scholarly journals Hypersensitivity of glacial summer temperatures in Siberia

2020 ◽  
Vol 16 (1) ◽  
pp. 371-386
Author(s):  
Pepijn Bakker ◽  
Irina Rogozhina ◽  
Ute Merkel ◽  
Matthias Prange
Keyword(s):  
Climate Model ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Cold Climate ◽  
Ice Age ◽  
Geological Evidence ◽  
Model Experiments ◽  
Community Earth System Model ◽  
Summer Temperatures ◽  
Glacial Periods

Abstract. Climate change in Siberia is currently receiving a lot of attention because large permafrost-covered areas could provide a strong positive feedback to global warming through the release of carbon that has been sequestered there on glacial–interglacial timescales. Geological evidence and climate model experiments show that the Siberian region also played an exceptional role during glacial periods. The region that is currently known for its harsh cold climate did not experience major glaciations during the last ice age, including its severest stages around the Last Glacial Maximum (LGM). On the contrary, it is thought that glacial summer temperatures were comparable to the present day. However, evidence of glaciation has been found for several older glacial periods. We combine LGM experiments from the second and third phases of the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) with sensitivity experiments using the Community Earth System Model (CESM). Together, these climate model experiments reveal that the intermodel spread in LGM summer temperatures in Siberia is much larger than in any other region of the globe and suggest that temperatures in Siberia are highly susceptible to changes in the imposed glacial boundary conditions, the included feedbacks and processes, and to the model physics of the different components of the climate model. We find that changes in the circumpolar atmospheric stationary wave pattern and associated northward heat transport drive strong local snow and vegetation feedbacks and that this combination explains the susceptibility of LGM summer temperatures in Siberia. This suggests that a small difference between two glacial periods in terms of climate, ice buildup or their respective evolution towards maximum glacial conditions can lead to strongly divergent summer temperatures in Siberia, allowing for the buildup of an ice sheet during some glacial periods, while during others, above-freezing summer temperatures preclude a multi-year snowpack from forming.

scholarly journals A high-resolution model of the 100 ka ice-age cycle

1997 ◽  
Vol 25 ◽  
pp. 58-65 ◽  
Author(s):  
L. Tarasov ◽  
W. R. Peltier
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Relaxation Times ◽  
Ice Age ◽  
Adjustment Process ◽  
Glacial Cycle ◽  
Ice Dynamics ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial

Significant improvements to the representation of climate forcing and mass-balance response in a coupled two-dimensional global energy balance climate model (EBM) and vertically integrated ice-sheet model (ISM) have led to the prediction of an ice-volume chronology for the most recent ice-age cycle of the Northern Hemisphere that is close to that inferred from the geological record. Most significant is that full glacial termination is delivered by the model without the need for new physical ingredients. In addition, a relatively close match is achieved between the Last Glacial Maximum (LGM) model ice topography and that of the recently-described ICE-4G reconstruction. These results suggest that large-scale climate system reorganization is not required to explain the main variations of the North American (NA) ice sheets over the last glacial cycle. Lack of sea-ice and marine-ice dynamics in the model leaves the situation over the Eurasian (EA) sector much more uncertain.The incorporation of a gravitationally self-consistent description of the glacial isostatic adjustment process demonstrates that the NA and EA bedrock responses can be adequately represented by simpler damped-relaxation models with characteristic time-scales of 3–5ka and 5 ka, respectively. These relaxation times agree with those independently inferred on the basis of postglacial relative sea-level histories.

scholarly journals Simulated climate variability in the region of Rapa Nui during the last millennium

2011 ◽  
Vol 7 (1) ◽  
pp. 381-395 ◽  
Author(s):  
C. Junk ◽  
M. Claussen
Keyword(s):  
Large Scale ◽  
Vegetation Change ◽  
Climate Model ◽  
Volcanic Eruptions ◽  
Easter Island ◽  
Ice Age ◽  
Vegetation Changes ◽  
Last Millennium ◽  
Climate Data ◽  
Climatic Fluctuations

Abstract. Easter Island, an isolated island in the Southeast Pacific, was settled by the Polynesians probably between 600 and 1200 AD and discovered by the Europeans in 1722 AD. While the Polynesians presumably found a profuse palm woodland on Easter Island, the Europeans faced a landscape dominated by grassland. Scientists have examined potential anthropogenic, biological and climatic induced vegetation changes on Easter Island. Here, we analyze observational climate data for the last decades and climate model results for the period 800–1750 AD to explore potential causes for a climatic-induced vegetation change. A direct influence of the ENSO phenomenon on the climatic parameters of Easter Island could not be found in the model simulations. Furthermore, strong climatic trends from a warm Medieval Period to a Little Ice Age or rapid climatic fluctuations due to large volcanic eruptions were not verifiable for the Easter Island region, although they are detectable in the simulations for many regions world wide. Hence we tentatively conclude that large-scale climate changes in the oceanic region around Easter Island might be too small to explain strong vegetation changes on the island over the last millennium.

scholarly journals A high-resolution model of the 100 ka ice-age cycle

1997 ◽  
Vol 25 ◽  
pp. 58-65 ◽  
Author(s):  
L. Tarasov ◽  
W. R. Peltier
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Relaxation Times ◽  
Ice Age ◽  
Adjustment Process ◽  
Glacial Cycle ◽  
Ice Dynamics ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial

Significant improvements to the representation of climate forcing and mass-balance response in a coupled two-dimensional global energy balance climate model (EBM) and vertically integrated ice-sheet model (ISM) have led to the prediction of an ice-volume chronology for the most recent ice-age cycle of the Northern Hemisphere that is close to that inferred from the geological record. Most significant is that full glacial termination is delivered by the model without the need for new physical ingredients. In addition, a relatively close match is achieved between the Last Glacial Maximum (LGM) model ice topography and that of the recently-described ICE-4G reconstruction. These results suggest that large-scale climate system reorganization is not required to explain the main variations of the North American (NA) ice sheets over the last glacial cycle. Lack of sea-ice and marine-ice dynamics in the model leaves the situation over the Eurasian (EA) sector much more uncertain.The incorporation of a gravitationally self-consistent description of the glacial isostatic adjustment process demonstrates that the NA and EA bedrock responses can be adequately represented by simpler damped-relaxation models with characteristic time-scales of 3–5ka and 5 ka, respectively. These relaxation times agree with those independently inferred on the basis of postglacial relative sea-level histories.

scholarly journals High-resolution leaf wax carbon and hydrogen isotopic record of the late Holocene paleoclimate in arid Central Asia

2015 ◽  
Vol 11 (4) ◽  
pp. 619-633 ◽  
Author(s):  
B. Aichner ◽  
S. J. Feakins ◽  
J. E. Lee ◽  
U. Herzschuh ◽  
X. Liu
Keyword(s):  
Central Asia ◽  
Late Holocene ◽  
Large Scale ◽  
Climate Model ◽  
Precipitation Amount ◽  
Ice Age ◽  
Late Winter ◽  
Arid Central Asia ◽  
Leaf Wax ◽  
D Values

Abstract. Central Asia is located at the confluence of large-scale atmospheric circulation systems. It is thus likely to be highly susceptible to changes in the dynamics of those systems; however, little is still known about the regional paleoclimate history. Here we present carbon and hydrogen isotopic compositions of n-alkanoic acids from a late Holocene sediment core from Lake Karakuli (eastern Pamir, Xinjiang Province, China). Instrumental evidence and isotope-enabled climate model experiments with the Laboratoire de Météorologie Dynamique Zoom model version 4 (LMDZ4) demonstrate that δ D values of precipitation in the region are influenced by both temperature and precipitation amount. We find that these parameters are inversely correlated on an annual scale, i.e., the climate has varied between relatively cool and wet and more warm and dry over the last 50 years. Since the isotopic signals of these changes are in the same direction and therefore additive, isotopes in precipitation are sensitive recorders of climatic changes in the region. Additionally, we infer that plants use year-round precipitation (including snowmelt), and thus leaf wax δ D values must also respond to shifts in the proportion of moisture derived from westerly storms during late winter and early spring. Downcore results give evidence for a gradual shift to cooler and wetter climates between 3.5 and 2.5 cal kyr BP, interrupted by a warm and dry episode between 3.0 and 2.7 kyr BP. Further cool and wet episodes occur between 1.9 and 1.5 and between 0.6 and 0.1 kyr BP, the latter coeval with the Little Ice Age. Warm and dry episodes from 2.5 to 1.9 and 1.5 to 0.6 kyr BP coincide with the Roman Warm Period and Medieval Climate Anomaly, respectively. Finally, we find a drying tend in recent decades. Regional comparisons lead us to infer that the strength and position of the westerlies, and wider northern hemispheric climate dynamics, control climatic shifts in arid Central Asia, leading to complex local responses. Our new archive from Lake Karakuli provides a detailed record of the local signatures of these climate transitions in the eastern Pamir.

Evidence from the Scandinavian Tree Line Since the Last Ice Age

1996 ◽  
Vol 7 (4) ◽  
pp. 357-364 ◽  
Author(s):  
Wibjörn Karlén ◽  
Johan Kuylenstierna
Keyword(s):  
Solar Activity ◽  
Volcanic Eruptions ◽  
Cold Climate ◽  
Ice Age ◽  
Alpine Glacier ◽  
Glacial Sediments ◽  
Carbon 14 ◽  
Pine Tree ◽  
Summer Temperatures ◽  
Last Ice Age

The focus of this paper is to investigate the possible correlation between changes in the Scandinavian climate and solar activity. Information about climatic changes in Sweden and Norway has been obtained from three sources: the carbon-14 dating of pine wood retrieved from above the present pine tree limit, studies of glacial sediments and the carbon dating of alpine glacier moraines. Alpine tree limits reveal that summer temperatures in general were warmer during the millennia following the last ice age. Superimposed on this general trend are fluctuations of a few hundred years duration. A period probably as cold as the last several hundred years occurred around 8200 years ago. Other severe cooling took place around 4500,2200 and 1200 years ago. The timing of major climatic events has been compared with solar activity as measured by carbn-14 changes and shows a good correlation with cold periods in Scandinavia for most of the last 8000 years. Deviations between carbn-14 anomalies and the climatic record may be due to volcanic eruptions increasing the concentration of sulfate aerosols in the atmosphere. A similarity between the periods of cold climate and carbon-14 levels indicates that solar variability may be an important factor for climate change.

scholarly journals Simulated climate variability in the region of Rapa Nui during the last millennium

2011 ◽  
Vol 7 (2) ◽  
pp. 579-586 ◽  
Author(s):  
C. Junk ◽  
M. Claussen
Keyword(s):  
Large Scale ◽  
Vegetation Change ◽  
Climate Model ◽  
Volcanic Eruptions ◽  
Ice Age ◽  
Vegetation Changes ◽  
Last Millennium ◽  
Climate Data ◽  
Rapa Nui ◽  
Climatic Fluctuations

Abstract. Rapa Nui, an isolated island in the Southeast Pacific, was settled by the Polynesians most likely around 1200 AD and was discovered by the Europeans in 1722 AD. While the Polynesians presumably found a profuse palm woodland on Rapa Nui, the Europeans faced a landscape dominated by grassland. Scientists have examined potential anthropogenic, biological and climatic induced vegetation changes on Rapa Nui. Here, we analyse observational climate data for the last decades and climate model results for the period 800–1750 AD to explore the potential for a climatic-induced vegetation change. A direct influence of the ENSO phenomenon on the climatic parameters of Rapa Nui could not be found in the model simulations. Furthermore, strong climatic trends from a warm Medieval Period to a Little Ice Age or rapid climatic fluctuations due to large volcanic eruptions were not verifiable for the Rapa Nui region, although they are detectable in the simulations for many regions world wide. Hence, we tentatively conclude that large-scale climate changes in the oceanic region around Rapa Nui might be too small to explain strong vegetation changes on the island over the last millennium.

Evolution of a quasi-steady breaking wave

1995 ◽  
Vol 302 ◽  
pp. 29-44 ◽  
Author(s):  
J. C. Lin ◽  
D. Rockwell
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Large Scale ◽  
Mixing Layer ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Small Scale ◽  
Radius Of Curvature ◽  
Breaking Wave ◽  
Large Radius

The stages of evolution of a quast-steady breaker from the onest of a capillary pattern to a fully evolved breaking wave are cgaracterized using high-image-density particle image velocimetry, which provides instrantaneous representations of the free surface and the patterns of vorticity beneath it. The initial stage, which sets in at a low value of Froude number, involves a capillary pattern along each trough-crest surface of a quasi-stationary wave. The successive crests of the capillary pattern exhihit increasing scale and culminate in a single largest-scale crest of the free surface. Immediately upstream of the large-scale crest, the capillary pattern shows counterclockwise concentrations of vorticity at its troughs and regions of clockwise vorticity beneath its crests. The onset of the final, largest-scale crest exhihits two forms: one involving no flow sparation; and the other exhibiting a small-scale separaed mixing layer. At an intermediate value of Froude number, a breaker occurs and the acpillary pattern is replaced by large-scale distortions of the free surface. The onset of separation, which involves flow deceleration along a region of the free surface having a large radius of curvature, leads to formation of a long mixing layeer, which has substantial levels of vorticity. Downstream of this breaker, the long-wavelength wave pattern is suppressed. At the largest value of Froude number, the onset of flow sparation rapidly occurs in conjunction with an abrupt change in slope of the surface, giving rise to vorticity concentrationa in the mixing layer.

scholarly journals Historical and idealized climate model experiments: an EMIC intercomparison

2012 ◽  
Vol 8 (4) ◽  
pp. 4121-4181 ◽  
Author(s):  
M. Eby ◽  
A. J. Weaver ◽  
K. Alexander ◽  
K. Zickfeld ◽  
A. Abe-Ouchi ◽  
...  
Keyword(s):  
Land Use ◽  
Carbon Cycle ◽  
Air Temperature ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Carbon Fluxes ◽  
Ice Age ◽  
Carbon Uptake ◽  
Model Experiments ◽  
Paleoclimate Reconstructions

Abstract. Both historical and idealized climate model experiments are performed with a variety of Earth System Models of Intermediate Complexity (EMICs) as part of a community contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO2, additional greenhouse gases, land-use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes seem to be underestimated. It is possible that recent modelled climate trends or climate-carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2x and 4x CO2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate-carbon feedbacks. The values from EMICs generally fall within the range given by General Circulation Models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows considerable synergy between land-use change and CO2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO2 between the Medieval Climate Anomaly and the Little Ice Age estimated from paleoclimate reconstructions. This in turn could be a result of errors in the reconstructions of volcanic and/or solar radiative forcing used to drive the models or the incomplete representation of certain processes or variability within the models. Given the datasets used in this study, the models calculate significant land-use emissions over the pre-industrial. This implies that land-use emissions might need to be taken into account, when making estimates of climate-carbon feedbacks from paleoclimate reconstructions.

scholarly journals Northern Hemisphere Stationary Waves in Future Climate Projections

2008 ◽  
Vol 21 (23) ◽  
pp. 6341-6353 ◽  
Author(s):  
Jenny Brandefelt ◽  
Heiner Körnich
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Stationary Wave ◽  
Climate Projections ◽  
Stationary Waves ◽  
Mean Flow ◽  
Wave Response

Abstract The response of the atmospheric large-scale circulation to an enhanced greenhouse gas (GHG) forcing varies among coupled global climate model (CGCM) simulations. In this study, 16 CGCM simulations of the response of the climate system to a 1% yr−1 increase in the atmospheric CO2 concentration to quadrupling are analyzed with focus on Northern Hemisphere winter. A common signal in 14 out of the 16 simulations is an increased or unchanged stationary wave amplitude. A majority of the simulations may be categorized into one of three groups based on the GHG-induced changes in the atmospheric stationary waves. The response of the zonal mean barotropic wind is similar within each group. Fifty percent of the simulations belong to the first group, which is categorized by a stationary wave with five waves encompassing the entire NH and a strengthening of the zonal mean barotropic wind. The second and third groups, respectively consisting of three and two simulations, are characterized by a broadening and a northward shift of the zonal mean barotropic wind, respectively. A linear model of barotropic vorticity is employed to study the importance of these mean flow changes to the stationary wave response. The linear calculations indicate that the GHG-induced mean wind changes explain 50%, 4%, and 37% of the stationary wave changes in each group, respectively. Thus, for the majority of simulations the zonal mean wind changes do significantly explain the stationary wave response.

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