scholarly journals The initiation of modern soft and hard Snowball Earth climates in CCSM4

2012 ◽  
Vol 8 (3) ◽  
pp. 907-918 ◽  
Author(s):  
J. Yang ◽  
W. R. Peltier ◽  
Y. Hu
Keyword(s):  
Solar Radiation ◽  
Sea Ice ◽  
Atmospheric Carbon Dioxide ◽  
Carbon Dioxide Concentration ◽  
Global Scale ◽  
Snowball Earth ◽  
Climate System Model ◽  
Geological Evidence ◽  
Radiative Forcings ◽  
The Impact

Abstract. Geochemical and geological evidence has suggested that several global-scale glaciation events occurred during the Neoproterozoic Era in the interval from 750–580 million years ago. The initiation of these glaciations is thought to have been a consequence of the combined influence of a low level of atmospheric carbon dioxide concentration and an approximately 6% weakening of solar luminosity. The latest version of the Community Climate System Model (CCSM4) is employed herein to explore the detailed combination of forcings required to trigger such extreme glaciation conditions under present-day circumstances of geography and topography. It is found that runaway glaciation occurs in the model under the following conditions: (1) an 8–9% reduction in solar radiation with 286 ppmv CO2 or (2) a 6% reduction in solar radiation with 70–100 ppmv CO2. These thresholds are moderately different from those found to be characteristic of the previously employd CCSM3 model reported recently in Yang et al. (2012a,b), for which the respective critical points corresponded to a 10–10.5% reduction in solar radiation with 286 ppmv CO2 or a 6% reduction in solar radiation with 17.5–20 ppmv CO2. The most important reason for these differences is that the sea ice/snow albedo parameterization employed in CCSM4 is believed to be more realistic than that in CCSM3. Differences in cloud radiative forcings and ocean and atmosphere heat transports also influence the bifurcation points. These results are potentially very important, as they are to serve as control on further calculations which will be devoted to an investigation of the impact of continental configuration. We demonstrate that there exist ''soft Snowball'' Earth states, in which the fractional sea ice coverage reaches approximately 60–65%, land masses in low latitudes are covered by perennial snow, and runaway glaciation does not develop. This is consistent with our previous results based upon CCSM3. Although our results cannot exclude the possibility of a ''hard Snowball'' solution, it is suggested that a ''soft Snowball'' solution for the Neoproterozoic remains entirely plausible.

scholarly journals The initiation of modern soft and hard Snowball Earth climates in CCSM4

2012 ◽  
Vol 8 (1) ◽  
pp. 1-29 ◽  
Author(s):  
J. Yang ◽  
W. R. Peltier
Keyword(s):  
Solar Radiation ◽  
Sea Ice ◽  
Global Scale ◽  
Snowball Earth ◽  
Climate System Model ◽  
Geological Evidence ◽  
Radiative Forcings ◽  
Ice Coverage ◽  
Low Latitudes ◽  
Atmospheric Heat

Abstract. Geochemical and geological evidence suggested that several global-scale glaciation events occurred during the Neoproterozoic era at 750–580 million years ago. The initiation of these glaciations is thought to have been a consequence of the combined influence of a result of low-level carbon dioxide and an approximately 6% weakening of solar luminosity. The latest version of the Community Climate System Model (CCSM4) is employed herein to explore the detailed combination of forcings required to trigger such extreme glaciation under present-day geography and topography conditions. It is found that runaway glaciation occurs in the model under the following conditions: (1) a 8–9% reduction in solar radiation with 286 ppmv CO2 or (2) a 6% reduction in solar radiation with 70–100 ppmv CO2. These thresholds are only moderately different from those found to be characteristic of the previous CCSM3 model reported recently in Yang et al. (2011a,b) for which the respective critical points corresponded to a 10–10.5% reduction in solar radiation with 286 ppmv CO2 or a 6% reduction in solar radiation with 17.5–20 ppmv CO2. The most important reason for these differences is that the sea-ice/snow albedo in CCSM4 is somewhat higher than in CCSM3. Differences in cloud radiative forcings and oceanic and atmospheric heat transports between CCSM3 and CCSM4 also influence the bifurcation points. The forcings required to trigger a "hard Snowball" Earth in either CCSM3 or CCSM4 may be not met by the conditions expected to be characteristic of the Neoproterozoic. Furthermore, there exist "soft Snowball" Earth states, in which the sea-ice coverage reaches approximately 60–65%, land masses in low latitudes are covered by perennial snow, and runaway glaciation does not develop. This is also qualitatively consistent with our previous results of the CCSM3 model. These results suggest that a "soft Snowball" solution for the Neoproterozoic is entirely plausible and may in fact be preferred.

Subtropical clouds stabilize near-Snowball Earth states

2020 ◽  
Author(s):  
Christoph Braun ◽  
Aiko Voigt ◽  
Johannes Hörner ◽  
Joaquim G. Pinto
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
General Circulation Models ◽  
Snowball Earth ◽  
Radiative Effects ◽  
Albedo Feedback ◽  
The Earth ◽  
Cloud Radiative Effects ◽  
Planetary Albedo ◽  
The Impact

<p>Atmospheric general circulation models developed for the Earth system include comprehensive parameterizations of clouds. Applying them to exoplanet atmospheres provides an opportunity to advance understanding of clouds, atmosphere dynamics, and their coupling in the context of planetary climate dynamics and habitability.</p><p>Here, we study a deep-time extreme climate of Earth as an example of the cold limit of the habitable zone. Geological evidence indicates near-global ice cover during the Neoproterozoic (1000 – 541 Million years ago) associated with considerable hysteresis of atmospheric CO<sub>2</sub>. The Snowball Earth hypothesis provides a straightforward interpretation of Neoproterozoic proxies based on a runaway of the sea-ice albedo feedback. However, the Snowball Earth hypothesis relies on the existence of local habitats to explain the survival of photosynthetic marine species on an entirely ice-covered planet. The Jormungand hypothesis may resolve this issue by considering a weakening of the sea-ice albedo feedback by exposure of dark bare sea ice when sea ice enters the subtropics. This potentially allows the Earth system to stabilize in a climate state - the Jormungand state - with near-global ice cover. Around the equator, a narrow strip of ocean remains ice-free, where life would have easily survived during the pan-glaciations.</p><p>The weakening of the sea-ice albedo feedback is based on the change of the meridional structure of planetary albedo with a moving sea-ice edge. While previous work focused on the contribution of surface albedo to planetary albedo, we here focus on the impact of subtropical and tropical cloudiness on planetary albedo. Enhanced cloudiness generally weakens the sea-ice albedo feedback and thus decreases the climate sensitivity of the Jormungand state, i.e. it stabilizes the Jormungand state. We analyze the impact of cloudiness on the stability of the Jormungand state in the general circulation models CAM3 and ICON-AES with idealized aquaplanet setups. While CAM3 shows significant CO<sub>2</sub>-hysteresis of the Jormungand state, ICON-AES exhibits no stable Jormungand state. Consistently, CAM3 exhibits stronger cloudiness than ICON-AES, especially in the subtropics. An analysis with a one-dimensional energy balance model shows that the Jormungand hysteresis strongly depends on the sensitivity of the planetary albedo to an advance of sea ice into the subtropics. Accordingly, we demonstrate that the absence of cloud-radiative effects within vertical columns in the subtropics drastically decreases the Jormungand hysteresis in CAM3.</p><p>Overall, the magnitude of the Jormungand hysteresis is tightly linked to the representation of cloud-radiative effects in general circulation models. Our results highlight the important role of uncertainties associated with cloud-radiative effects for climate feedbacks on planet Earth in the context of extreme climates, such as they have occurred in Earth’s deep past or might be found on Earth-like planets. In consequence, this also stresses the need and challenges of accounting for adequate cloud modeling for planetary climates.</p>

The Initiation of Modern “Soft Snowball” and “Hard Snowball” Climates in CCSM3. Part I: The Influences of Solar Luminosity, CO2 Concentration, and the Sea Ice/Snow Albedo Parameterization

2012 ◽  
Vol 25 (8) ◽  
pp. 2711-2736 ◽  
Author(s):  
Jun Yang ◽  
W. Richard Peltier ◽  
Yongyun Hu
Keyword(s):  
Solar Radiation ◽  
Sea Ice ◽  
Open Water ◽  
Co2 Concentration ◽  
Critical Conditions ◽  
Climate System Model ◽  
Snow Albedo ◽  
Solar Luminosity ◽  
The Earth ◽  
Continental Ice Sheets

Abstract The “Snowball Earth” hypothesis, proposed to explain the Neoproterozoic glacial episodes in the period 750–580 million years ago, suggested that the earth was globally covered by ice/snow during these events. This study addresses the problem of the forcings required for the earth to enter such a state of complete glaciation using the Community Climate System Model, version 3 (CCSM3). All of the simulations performed to address this issue employ the geography and topography of the present-day earth and are employed to explore the combination of factors consisting of total solar luminosity, CO2 concentration, and sea ice/snow albedo parameterization that would be required for such an event to occur. The analyses demonstrate that the critical conditions beyond which runaway ice–albedo feedback will lead to global freezing include 1) a 10%–10.5% reduction in solar radiation with preindustrial greenhouse gas concentrations; 2) a 6% reduction in solar radiation with 17.5 ppmv CO2; or 3) 6% less solar radiation and 286 ppmv CO2 if sea ice albedo is equal to or greater than 0.60 with a snow albedo of 0.78, or if sea ice albedo is 0.58 with a snow albedo equal to or greater than 0.80. These bifurcation points are very sensitive to the sea ice and snow albedo parameterizations. Moreover, “soft Snowball” solutions are found in which tropical open water oceans stably coexist with year-round snow-covered low-latitude continents, implying that tropical continental ice sheets would actually be present. The authors conclude that a “soft Snowball” is entirely plausible, in which the global sea ice fraction may reach as high as 76% and sea ice margins may extend to 10°S(N) latitudes.

Rising CO2 and pollen production of common ragweed (Ambrosia artemisiifolia L.), a known allergy-inducing species: implications for public health.

2000 ◽  
Vol 27 (10) ◽  
pp. 893 ◽  
Author(s):  
Lewis H. Ziska ◽  
Frances A. Caulfield
Keyword(s):  
Public Health ◽  
Atmospheric Carbon Dioxide ◽  
Carbon Dioxide Concentration ◽  
Ambrosia Artemisiifolia ◽  
Pollen Production ◽  
Potential Growth ◽  
Plant Weight ◽  
Common Ragweed ◽  
Total Plant ◽  
The Impact

Although environmental factors such as precipitation and temperature are recognized as influencing pollen production, the impact of rising atmospheric carbon dioxide concentration ([CO2]) on the potential growth and pollen production of hay-fever-inducing plants is unknown. Here we present measurements of growth and pollen production of common ragweed (Ambrosia artemisiifolia L.) from pre-industrial [CO2] (280 mol mol–1) to current concentrations (370 mol mol–1) to a projected 21st century concentration (600 mol mol–1). We found that exposure to current and elevated [CO2] increased ragweed pollen production by 131 and 320%, respectively, compared to plants grown at pre-industrial [CO2]. The observed stimulations of pollen production from the pre-industrial [CO2] were due to an increase in the number (at 370 mol mol–1) and number and size (at 600 mol mol–1) of floral spikes. Overall, floral weight as a percentage of total plant weight decreased (from 21% to 13%), while investment in pollen increased (from 3.6 to 6%) between 280 and 600 mol mol–1 CO2. Our results suggest that the continuing increase in atmospheric [CO2] could directly influence public health by stimulating the growth and pollen production of allergy-inducing species such as ragweed.

scholarly journals <sup>10</sup>Be in last deglacial climate simulated by ECHAM5-HAM – Part 1: Climatological influences on <sup>10</sup>Be deposition

2013 ◽  
Vol 9 (4) ◽  
pp. 3681-3709 ◽  
Author(s):  
U. Heikkilä ◽  
S. J. Phipps ◽  
A. M. Smith
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Mass Conservation ◽  
High Latitudes ◽  
Last Deglaciation ◽  
Surface Cooling ◽  
Climate System Model ◽  
The Last Deglaciation ◽  
The Impact ◽  
Atmospheric Concentrations

Abstract. Reconstruction of solar irradiance has only been possible for the Holocene so far. During the last deglaciation two solar proxies (10Be and 14C) deviate strongly, both of them being influenced by climatic changes in a different way. This work addresses the climate influence on 10Be deposition by means of ECHAM5-HAM atmospheric aerosol-climate model simulations, forced by sea surface temperatures and sea ice extent created by the coupled climate system model CSIRO Mk3L. Three time slice simulations were performed during the last deglaciation: 10 000 BP ("10k"), 11 000 BP ("11k") and 12 000 BP ("12k"), each 30 yr long. The same 10Be production rate was used in each simulation to isolate the impact of climate on 10Be deposition. The changes are found to follow roughly the reduction in the greenhouse gas concentrations within the simulations. The 10k and 11k simulations produce a surface cooling which is symmetrically amplified in the 12k simulation. The precipitation rate is only slightly reduced at high latitudes, but there is a northward shift in the polar jet in the Northern Hemisphere and the stratospheric westerly winds are significantly weakened. These changes occur where the sea ice change is largest in the deglaciation simulations. This leads to a longer residence time of 10Be in the stratosphere by 30 (10k and 11k) to 80 (12k) days, heavily increasing the atmospheric concentrations. Furthermore the shift of westerlies in the troposphere leads to an increase of tropospheric 10Be concentrations, especially at high latitudes. The contribution of dry deposition generally increases, but decreases where sea ice changes are largest. In total, the 10Be deposition rate changes by no more than 20% at mid- to high latitudes, but by up to 50% in the tropics. We conclude that on "long" time scales (a year to a few years), climatic influences on 10Be deposition remain small even though atmospheric concentrations can vary significantly. Averaged over a longer period all 10Be produced has to be deposited by mass conservation. This dominates over any climatic influences on 10Be deposition. Snow concentrations, however, do not follow mass conservation and can potentially be impacted more by climate due to precipitation changes. Quantifying the impact of deglacial climate modulation on 10Be in terms of preserving the solar signal locally is analysed in an accompanying paper (Heikkilä et al., 2013).

scholarly journals A biologically driven directional change in susceptibility to global-scale glaciation during the Precambrian-Cambrian transition

2018 ◽  
Author(s):  
Richard A. Boyle ◽  
Carolin R. Löscher
Keyword(s):  
Land Surface ◽  
Climate Models ◽  
Abiotic Factors ◽  
Global Scale ◽  
Snowball Earth ◽  
Critical Aspect ◽  
Geological Evidence ◽  
Directional Change ◽  
Temperature Window ◽  
Tectonic Boundary

Integrated geological evidence suggests that grounded ice sheets occurred at sea level across all latitudes during two intervals within the Neoproterozoic era; the “snowball Earth” (SBE) events. Glacial events at ~730 and ~650 million years ago (Ma) were probably followed by a less severe but nonetheless global-scale glaciation at ~580Ma, immediately preceding the proliferation of the first fossils exhibiting unambiguous animal-like form. Existing modelling identifies weathering-induced CO2 draw-down as a critical aspect of glacial inception, but ultimately attributes the SBE phenomenon to unusual tectonic boundary conditions. Here we suggest that the evident directional decrease in Earth’s susceptibility to a SBE suggests that such a-directional abiotic factors are an insufficient explanation for the lack of SBE events since ~580 Ma. Instead we hypothesize that the terrestrial biosphere’s capacity to sustain a given level of biotic weathering-enhancement under suboptimal/declining temperatures, itself decreased over time: because lichens (with a relatively robust tolerance of sub-optimal temperatures) were gradually displaced on the land surface by more complex photosynthetic life (with a narrower temperature window for growth). We use a simple modelling exercise to highlight the critical (but neglected) importance of the temperature sensitivity of the biotic weathering enhancement factor and discuss the likely values of key parameters in relation to both experiments and the results of complex climate models. We show how the terrestrial biosphere’s capacity to sustain a given level of silicate-weathering-induced CO2 draw-down is critical to the temperature/greenhouse forcing at which SBE initiation is conceivable. We do not dispute the importance of low degassing rate and other tectonic factors, but propose that the unique feature of the Neoproterozoic was biology’s capacity to tip the system over the edge into a runaway ice-albedo feedback; compensating for the self-limiting decline in weathering rate during the temperature decrease on the approach to glaciation. Such compensation was more significant in the Neoproterozoic than the Phanerozoic due, ultimately, to changes in the species composition of the weathering interface over the course of evolutionary time.

scholarly journals The Impact of Milankovitch Solar Radiation Variations on Sea-Ice and Air Temperature in a Coupled Energy-Balance Climate-Sea-Ice Model

1990 ◽  
Vol 14 ◽  
pp. 144-147 ◽  
Author(s):  
Tamara Shapiro Ledley
Keyword(s):  
Solar Radiation ◽  
Sea Ice ◽  
Air Temperature ◽  
Energy Transport ◽  
Model Simulation ◽  
Surface Air Temperature ◽  
Ice Thickness ◽  
Sea Ice Thickness ◽  
The Mean ◽  
The Impact

The sensitivity of thermodynamically-varying sea-ice and surface air temperature to variations in solar radiation on the 104 to 105 time scales is examined in this study. Model simulation results show the mean annual sea-ice thickness is very sensitive to the magnitude of midsummer solar radiation. During periods of high midsummer solar radiation between 115 ka B.P. and the present the sea ice is thinner, producing larger summer time leads and longer periods of open ocean. This has an effect on the mean annual sea-ice thickness, but not on the mean annual air temperature. However, the changes in sea ice are accompanied by similar variations in the summer surface air temperature, which are the result of the variations in the solar radiation and meridional energy transport.

scholarly journals The Impact of Milankovitch Solar Radiation Variations on Sea-Ice and Air Temperature in a Coupled Energy-Balance Climate-Sea-Ice Model

1990 ◽  
Vol 14 ◽  
pp. 144-147 ◽  
Author(s):  
Tamara Shapiro Ledley
Keyword(s):  
Solar Radiation ◽  
Sea Ice ◽  
Air Temperature ◽  
Energy Transport ◽  
Model Simulation ◽  
Surface Air Temperature ◽  
Ice Thickness ◽  
Sea Ice Thickness ◽  
The Mean ◽  
The Impact

The sensitivity of thermodynamically-varying sea-ice and surface air temperature to variations in solar radiation on the 104 to 105 time scales is examined in this study. Model simulation results show the mean annual sea-ice thickness is very sensitive to the magnitude of midsummer solar radiation. During periods of high midsummer solar radiation between 115 ka B.P. and the present the sea ice is thinner, producing larger summer time leads and longer periods of open ocean. This has an effect on the mean annual sea-ice thickness, but not on the mean annual air temperature. However, the changes in sea ice are accompanied by similar variations in the summer surface air temperature, which are the result of the variations in the solar radiation and meridional energy transport.

scholarly journals The Transient and Equilibrium Climate Response to Rapid Summertime Sea Ice Loss in CCSM4

2016 ◽  
Vol 29 (2) ◽  
pp. 401-417 ◽  
Author(s):  
Russell Blackport ◽  
Paul J. Kushner
Keyword(s):  
Standard Deviation ◽  
Sea Ice ◽  
Transient Response ◽  
Geopotential Height ◽  
General Circulation ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Climate System Model ◽  
Study Results ◽  
The Impact

Abstract The impact that disappearing Arctic sea ice will have on the atmospheric circulation and weather variability remains uncertain. In this study, results are presented from a sea ice perturbation experiment using the coupled Community Climate System Model, version 4 (CCSM4). By decreasing the albedo of the sea ice, the impact of an ice-free summertime Arctic on the coupled ocean–atmosphere system is isolated in an idealized but energetically self-consistent way. The multicentury equilibrium response is examined, as well as the transient response in an initial condition ensemble. The perturbation drives pronounced year-round sea ice thinning, Arctic warming, Arctic amplification, and moderate global warming. Even in the almost complete absence of summertime sea ice, the atmospheric general circulation response is very weak and the transient response is small compared to the internal variability. Surface temperature variability is reduced on all time scales over most of the middle and high latitudes with a 50% reduction in the standard deviation of temperature over the Arctic Ocean. The reduction is attributed to decreased temperature gradients and increased maritime influence once the sea ice melts. This reduced variability extends weakly into the variability of the midlatitude and free tropospheric geopotential height (less than 10% reduction in the standard deviation). Consistently, eddy geopotential height variability is found to decrease while geopotential isopleth meandering, which reflects Arctic amplified warming, increases moderately. The sign of these changes is consistent with recent observations, but the size of these changes is relatively small.

scholarly journals Arctic Ocean sea ice snow depth evaluation and bias sensitivity in CCSM

2013 ◽  
Vol 7 (6) ◽  
pp. 1887-1900 ◽  
Author(s):  
B. A. Blazey ◽  
M. M. Holland ◽  
E. C. Hunke
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Snow Depth ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Blowing Snow ◽  
Climate System Model ◽  
The Arctic Ocean ◽  
Future Work ◽  
The Impact

Abstract. Sea ice cover in the Arctic Ocean is a continued focus of attention. This study investigates the impact of the snow overlying the sea ice in the Arctic Ocean. The impact of snow depth biases in the Community Climate System Model (CCSM) is shown to impact not only the sea ice, but also the overall Arctic climate. Following the identification of seasonal biases produced in CCSM simulations, the thermodynamic transfer through the snow–ice column is perturbed to determine model sensitivity to these biases. This study concludes that perturbations on the order of the observed biases result in modification of the annual mean conductive flux through the snow–ice column of 0.5 W m2 relative to an unmodified simulation. The results suggest that the ice has a complex response to snow characteristics, with ice of different thicknesses producing distinct reactions. Our results indicate the importance of an accurate simulation of snow on the Arctic sea ice. Consequently, future work investigating the impact of current precipitation biases and missing snow processes, such as blowing snow, densification, and seasonal changes, is warranted.

Sign in / Sign up

Export Citation Format

Share Document