Model-dependence of the CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; threshold for melting the hard Snowball Earth

Hu, Yongyun; Yang, Jianqiang; Ding, Feng; Peltier, W. R.

doi:10.5194/cp-7-17-2011

Cited by 29 publications

(43 citation statements)

References 28 publications

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“…Snow depth varies with time, depending on the hydrological cycle, and surface temperature is determined by the surface energy budget. The sea-ice/snow prescription employed herein is similar to that in Le Hir et al (2007) and Hu et al (2011a).…”

Section: Model Description and Experimental Designmentioning

confidence: 81%

“…Poulsen et al, 2001;Voigt and Marotzke, 2010;Pierrehumbert et al, 2011;Hu et al, 2011a;Yang et al, 2012a,b,c) and have furthermore neglected the fact that O 3 concentration for both the stratosphere and the troposphere in the Neoproterozoic era could have been significantly lower than the present-day level, which could significantly alter the CO 2 thresholds for both initiation and deglaciation of the Snowball Earth as we will show below.…”

Section: J Yang Et Al: Effects Of Ozone On the Climate Of A Snowbalmentioning

confidence: 99%

“…Methane concentration is 1.714 ppmv; nitrous oxide concentration is 0.311 ppmv; and the concentrations of both aerosols and CFCs are set to zero. Surface pressure is fixed at 1.0 bar; the influence of pressure broadening associated with a high level of CO 2 , as discussed in Hu et al (2011a), can be safely ignored in these simulations. Solar luminosity is fixed at 94 % of the present-day level, i.e.…”

Section: Model Description and Experimental Designmentioning

confidence: 99%

“…For deglaciation is assumed, simulations with different models have also suggested different thresholds (Hyde et al, 2000;Tajika, 2003;Pierrehumbert, 2004Pierrehumbert, , 2005Le Hir et al, 2007). The most recent study of Hu et al (2011a) showed that the CO 2 threshold is approximately 0.21 bars in a radiative-convective model and approximately 0.38 bars in a GCM when pressurebroadening and collision-induced absorption of CO 2 at high pressure and high levels of CO 2 are taken into account. With the assumption of a dust zone at the surface in the tropics, which would lower tropical surface albedo, the CO 2 threshold required to trigger the deglaciation would drop to approximately 0.1 bar (Abbot and Pierrehumbert, 2010;Le Hir et al, 2010;Li and Pierrehumbert, 2011).…”

Section: Introductionmentioning

confidence: 99%

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Radiative effects of ozone on the climate of a Snowball Earth

Yang

Peltier

2012

Clim. Past

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Abstract. Some geochemical and geological evidence has been interpreted to suggest that the concentration of atmospheric oxygen was only 1-10 % of the present level in the time interval from 750 to 580 million years ago when several nearly global glaciations or Snowball Earth events occurred. This low concentration of oxygen would have been accompanied by a lower ozone concentration than exists at present. Since ozone is a greenhouse gas, this change in ozone concentration would alter surface temperature, and thereby could have an important influence on the climate of the Snowball Earth. Previous works that have focused either on initiation or deglaciation of the proposed Snowball Earth has not taken the radiative effects of ozone changes into account. We address this issue herein by performing a series of simulations using an atmospheric general circulation model with various ozone concentrations.Our simulation results demonstrate that, as ozone concentration is uniformly reduced from 100 % to 50 %, surface temperature decreases by approximately 0.8 K at the Equator, with the largest decreases located in the middle latitudes reaching as high as 2.5 K. When ozone concentration is reduced and its vertical and horizontal distribution is simultaneously modulated, surface temperature decreases by 0.4-1.0 K at the Equator and by 4-7 K in polar regions. These results here have uncertainties, depending on model parameterizations of cloud, surface snow albedo, and relevant feedback processes, while they are qualitatively consistent with radiative-convective model results that do not involve such parameterizations and feedbacks. These results suggest that ozone variations could have had a moderate impact on the climate during the Neoproterozoic glaciations.

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Section: Model Description and Experimental Designmentioning

confidence: 81%

Section: J Yang Et Al: Effects Of Ozone On the Climate Of A Snowbalmentioning

confidence: 99%

Section: Model Description and Experimental Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Radiative effects of ozone on the climate of a Snowball Earth

Yang

Peltier

2012

Clim. Past

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“…The radiative transfer module of the model is approximately valid for atmospheres with CO 2 concentration lower than 200,000 ppmv and water-vapor column amount less than 1,200 kg m −2 , although the simulated climate is very slightly colder than it should be (20,21). For CO 2 levels above 200,000 ppmv, the effects of pressure broadening and collision-induced CO 2 absorption become significant (22,23). In addition, we also examine climate states for exoplanets closer to both inner and outer edges of the HZ by performing simulations with a sequence of stellar radiation fluxes of 700, 866, 1,200, and 1,400 W m −2 and with constant CO 2 concentration of 355 ppmv.…”

Section: Methodsmentioning

confidence: 99%

Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars

Yang

2013

Proc. Natl. Acad. Sci. U.S.A.

134

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The distinctive feature of tidally locked exoplanets is the very uneven heating by stellar radiation between the dayside and nightside. Previous work has focused on the role of atmospheric heat transport in preventing atmospheric collapse on the nightside for terrestrial exoplanets in the habitable zone around M dwarfs. In the present paper, we carry out simulations with a fully coupled atmosphere-ocean general circulation model to investigate the role of ocean heat transport in climate states of tidally locked habitable exoplanets around M dwarfs. Our simulation results demonstrate that ocean heat transport substantially extends the area of open water along the equator, showing a lobster-like spatial pattern of open water, instead of an "eyeball." For sufficiently high-level greenhouse gases or strong stellar radiation, ocean heat transport can even lead to complete deglaciation of the nightside. Our simulations also suggest that ocean heat transport likely narrows the width of M dwarfs' habitable zone. This study provides a demonstration of the importance of exooceanography in determining climate states and habitability of exoplanets.planetary climate | exoplanet habitability | superEarth M dwarf stars are the most common type of star in the Universe (1). The habitable zone (HZ) around M stars is close to such stars because of their weak luminosity (2). In consequence, habitable exoplanets orbiting M stars are likely to be tidally locked to their primary stars, so that one side of tidallocking exoplanets permanently faces stars, and the other side remains dark. Previous studies have demonstrated the role of atmospheric heat transport in preventing atmospheric collapse on the nightside of terrestrial exoplanets located in the HZ of M stars (3-10). For a planet with an extensive ocean, its climate and habitability also involves ocean heat transport, which is known to be important in Earth's climate (11). None of the existing studies has considered the role of ocean heat transport. Moreover, the climate also involves the spatial distribution of open water versus ice and the question of whether the planet becomes locked in a globally glaciated Snowball state. Simulation with a comprehensive Earth atmospheric general circulation model (AGCM) coupled to a slab ocean, without dynamic ocean heat transport, revealed an "eyeball" climate state, with a round area of open ocean centered at the substellar point and complete ice coverage on the nightside, even for very high CO 2 concentrations (4). In the presence of sea ice, ocean heat transport is likely to be especially important, because it is known from studies of the Snowball Earth phenomenon in Earth-like conditions that ocean heat transport is very effective in holding back the advance of the sea-ice margin (12-14). The distribution of sea ice on tidally locked exoplanets is only an issue for M stars, because planets with sufficiently dense atmospheres orbiting hotter stars in orbits close enough to yield tidal locking are likely to be too hot to permit ice and may ...

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Snowball Earth: Asynchronous coupling of sea‐glacier flow with a global climate model

2017

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During Snowball Earth episodes of the Neoproterozoic and Paleoproterozoic, limited amounts of tropical open ocean (Jormungand), or tropical ocean with thin ice cover, would help to explain (1) vigorous glacial activity in low latitudes, (2) survival of photosynthetic life, and (3) deglacial recovery without excessive buildup of atmospheric CO2. Some previous models have suggested that tropical open ocean or thin‐ice cover is possible; however, its viability in the presence of kilometer‐thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively. Here we describe a new method of asynchronously coupling a zonal sea‐glacier model with a 3‐D global climate model and apply it to Snowball Earth. Equilibrium curves of ice line versus CO2 are mapped out, as well as their dependence on ocean heat transport efficiency, sea‐glacier flow, and other model parameters. No climate states with limited tropical open ocean or thin ice are found in any of our model runs, including those with sea glaciers. If this result is correct, then other refugia such as cryoconite pans would have been required for life to survive. However, the reasons for the differences between our results and others should first be resolved. It is suggested that small‐scale convective dynamics, affecting fractional snow cover in low latitudes, may be a critical factor accounting for these differences.

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Model-dependence of the CO<sub>2</sub> threshold for melting the hard Snowball Earth

Cited by 29 publications

References 28 publications

Radiative effects of ozone on the climate of a Snowball Earth

Radiative effects of ozone on the climate of a Snowball Earth

Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars

Snowball Earth: Asynchronous coupling of sea‐glacier flow with a global climate model

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