Papers on the deglaciation of snowball Earth

This is a list of papers on the deglaciation of snowball Earth, i.e. papers studying how Earth came back from the “snowball” state. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (August 8, 2011): Font et al. (2010) added. Thanks to Eric Font for pointing out (see the comment section below).
UPDATE (July 25, 2011): Hu et al. (2011) added. Thanks to Jun Yang for pointing it out (see the comment section below).

Model-dependence of the CO₂ threshold for melting the hard Snowball Earth – Hu et al. (2011) “One of the critical issues of the Snowball Earth hypothesis is the CO₂ threshold for triggering the deglaciation. Using Community Atmospheric Model version 3.0 (CAM3), we study the problem for the CO₂ threshold. Our simulations show large differences from previous results (e.g. Pierrehumbert, 2004, 2005; Le Hir et al., 2007). At 0.2 bars of CO₂, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO₂ in Le Hir et al. (2007). It is found that the difference of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO₂. At 0.2 bars of CO₂, CAM3 yields 117 Wm−2 of clear-sky greenhouse effect and 32 Wm−2 of longwave cloud forcing, versus only about 77 Wm−2 and 10.5 Wm−2 in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than that in Pierrehumbert (2005). Effects of pressure broadening and collision-induced absorption are also studied using a radiative-convective model and CAM3. Both effects substantially increase surface temperature and thus lower the CO₂ threshold. The radiative-convective model yields a CO₂ threshold of about 0.21 bars with surface albedo of 0.663. Without considering the effects of pressure broadening and collision-induced absorption, CAM3 yields an approximate CO₂ threshold of about 1.0 bar for surface albedo of about 0.6. However, the threshold is lowered to 0.38 bars as both effects are considered.” Hu, Y., Yang, J., Ding, F., and Peltier, W. R., Clim. Past, 7, 17-25, doi:10.5194/cp-7-17-2011, 2011. [Full text]

Fast or slow melting of the Marinoan snowball Earth? The cap dolostone record – Font et al. (2010) “The end of the Neoproterozoic era is punctuated by two global glacial events marked by the presence of glacial deposits overlaid by cap carbonates. Duration of glacial intervals is now consistently constrained to 3–12 million years but the duration of the post-glacial transition is more controversial due to the uncertainty in cap dolostone sedimentation rates. Indeed, the presence of several stratabound magnetic reversals in Brazilian cap dolostones recently questioned the short sedimentation duration (a few thousand years at most) that was initially suggested for these rocks. Here, we present new detailed magnetostratigraphic data of the Mirassol d’Oeste cap dolostones (Mato Grosso, Brazil) and “bomb-spike” calibrated AMS ¹⁴C data of microbial mats from the Lagoa Vermelha (Rio de Janeiro, Brazil). We also compile sedimentary, isotopic and microbiological data from post-Marinoan outcrops and/or recent depositional analogues in order to discuss the deposition rate of Marinoan cap dolostones and to infer an estimation of the deglaciation duration in the snowball Earth aftermath. Taken together, the various data point to a sedimentation duration in the range of a few 10⁵ years.” E. Font, A. Nédélec, R.I.F. Trindade and C. Moreau, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 295, Issues 1-2, 1 September 2010, Pages 215-225, doi:10.1016/j.palaeo.2010.05.039.

Mudball: Surface dust and Snowball Earth deglaciation – Abbot & Pierrehumbert (2010) “Here we argue that over the lifetime of a Snowball event, ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation. This idea leads to the prediction that clay drapes found on top of Neoproterozoic glaciations should be thicker in tropical than extratropical regions. We test this idea by running the FOAM general circulation model (GCM) with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes Snowball deglaciation at pCO₂ = 0.01–0.1 bar in a reasonable regime of these parameters.” [Full text]

Toward the snowball earth deglaciation… – Le Hir et al. (2010) “The current state of knowledge suggests that the Neoproterozoic snowball Earth is far from deglaciation even at 0.2 bars of CO₂. Since understanding the termination of the fully ice-covered state is essential to sustain, or not, the snowball Earth theory, we used an Atmospheric General Climate Model (AGCM) to explore some key factors which could induce deglaciation. After testing the models’ sensitivity to their parameterizations of clouds, CO₂ and snow, we investigated the warming effect caused by a dusty surface, associated with ash release during a mega-volcanic eruption. We found that the snow aging process, its dirtiness and the ash deposition on the snow-free ice are key factors for deglaciation. Our modelling study suggests that, under a CO₂ enriched atmosphere, a dusty snowball Earth could reach the deglaciation threshold.” [Full text]

Scenario for the evolution of atmospheric pCO₂ during a snowball Earth – Le Hir et al. (2008) “In this contribution, we question this assumed linear accumulation of CO₂ into the atmosphere. Using a numerical model of the carbon-alkalinity cycles, we suggest that during global glaciations, even a limited area of open waters (103 km2) allows an efficient atmospheric CO₂ diffusion into the ocean. This exchange implies that the CO₂ consumption through the low-temperature alteration of the oceanic crust persists throughout the glaciation. Furthermore, our model shows that rising CO₂ during the glaciation increases the efficiency of this sink through the seawater acidification. As a result, the atmospheric CO₂ evolution is asymptotic, limiting the growth rate of the atmospheric carbon reservoir. Even after the maximum estimated duration of the glaciation (30 m.y.), the atmospheric CO₂ is far from reaching the minimum deglaciation threshold (0.29 bar).”

Sedimentary challenge to Snowball Earth – Allen & Etienne (2008) “However, sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans throughout the glacial cycle. The sedimentary evidence therefore indicates that despite the severity of glaciation, some oceans must have remained ice-free. Significant areas of open ocean have important implications for the survival and diversification of life and for the workings of the global carbon cycle.”

Investigating plausible mechanisms to trigger a deglaciation from a hard snowball Earth – Le Hir et al. (2007) “Those results show that the cause of deglaciation is unresolved and the discussion about a plausible escape scenario remains open. For this reason, to test and to determine the sensitivity and efficiency of the greenhouse effect during a ‘hard’ snowball–Earth, we compare the FOAM results with those of LMDz (AGCM of the ‘Laboratoire de météorologie dynamique’). The preliminary results show that LMDz is much more sensitive to a CO₂ increase than FOAM. This article shows that among processes that could explain this difference, the key factor is the cloud parameterization and its interaction with the convective scheme. These simulations suggest that the CO₂ threshold is dependent on the GCM parameterization used, and could be lower than the one suggested by FOAM. Moreover, to investigate other plausible mechanisms able to melt the equatorial ice, we have tested the CH₄ impact with a simple 0D model, INCA-ZD. Results show that the balance between the residence times of CH₄ in a ‘hard’ snowball–Earth scenario is largely overcome by the extinction of the organic source, which means that CO₂ remains the only greenhouse gas warming the snowball Earth.” [Full text]

Deglaciating the snowball Earth: Sensitivity to surface albedo – Lewis et al. (2006) “Here we attempt to quantify the relative sensitivity of different surface albedos, using the University of Victoria’s Earth System Climate Model, to deglaciating the snowball Earth. We investigate the sensitivity of ice, snow, and land albedo on the minimum CO₂ greenhouse forcing required for deglaciating the Neoproterozoic snowball Earth. We find that the amount of CO₂ forcing required for deglaciation can vary by nearly an order of magnitude within accepted albedo ranges.” [Full text]

Climate dynamics of a hard snowball Earth – Pierrehumbert (2005) “The problem of deglaciating a globally ice-covered (“hard snowball”) Earth is examined using a series of general circulation model simulations. The aim is to determine the amount of CO₂ that must be accumulated in the atmosphere in order to trigger deglaciation. … In contrast to prevailing expectations, the hard snowball Earth is found to be nearly 30 K short of deglaciation, even at .2 bars. The very cold climates arise from a combination of the extreme seasonal and diurnal cycle, lapse rate effects, snow cover, and weak cloud effects. Several aspects of the atmospheric dynamics are examined in detail. The simulations indicate that the standard scenario, wherein snowball termination occurs after a few tenths of a bar of CO 2 has built up following cessation of weathering, is problematic. However, the climate was found to be sensitive to details of a number of parameterized physical processes, notably clouds and heat transfer through the stable boundary layer. It is not out of the question that other parameterization suites might permit deglaciation. The results should not be construed as meaning that the hard snowball state could not have occurred, but only that deglaciation requires the operation of as-yet undiscovered processes that would enhance the climate sensitivity.” [Full text]

High levels of atmospheric carbon dioxide necessary for the termination of global glaciation – Pierrehumbert (2004) “Termination of such ‘hard snowball Earth’ climate states has been proposed to proceed from accumulation of carbon dioxide in the atmosphere4. Many salient aspects of the snowball scenario depend critically on the threshold of atmospheric carbon dioxide concentrations needed to trigger deglaciation2, 5. Here I present simulations with a general circulation model, using elevated carbon dioxide levels to estimate this deglaciation threshold. The model simulates several phenomena that are expected to be significant in a ‘snowball Earth’ scenario, but which have not been considered in previous studies with less sophisticated models, such as a reduction of vertical temperature gradients in winter, a reduction in summer tropopause height, the effect of snow cover and a reduction in cloud greenhouse effects. In my simulations, the system remains far short of deglaciation even at atmospheric carbon dioxide concentrations of 550 times the present levels (0.2 bar of CO₂). I find that at much higher carbon dioxide levels, deglaciation is unlikely unless unknown feedback cycles that are not captured in the model come into effect.”

CO₂ levels required for deglaciation of a “near‐snowball” Earth – Crowley et al. (2001) “Although 0.1 to 0.3 of an atmosphere of CO₂ (∼300 to 1000 X) is required for deglaciation of a “Snowball Earth,” the “exit” CO₂ levels for an open water solution could be significantly less. In this paper we utilize a coupled climate/ice sheet model to demonstrate four points: (1) the open water solution can be simulated in the coupled model if the sea ice parameter is adjusted slightly; (2) a major reduction in ice volume from the open water/equatorial ice solution occurs at a CO₂ level of about 4X present values—about two orders of magnitude less than required for exit from the “hard” snowball initial state; (3) additional CO₂ increases are required to get fuller meltback of the ice; and (4) the open water solution exhibits hysteresis properties, such that climates with the same level of CO₂ may evolve into either the snowball, open water, or a warmer world solution, with the trajectory depending on initial conditions.” [Full text]

Susceptibility of the early Earth to irreversible glaciation caused by carbon dioxide clouds – Caldeira & Kasting (1992) “Had such a transient global glaciation occurred in the distant past when solar luminosity was low, it might have been irreversible because of the formation of highly reflective CO₂ clouds, similar to those encountered in climate simulations of early Mars. … In the ice-covered state little or no silicate rock would be exposed to weathering, so CO₂ from metamorphic and mantle sources could accumulate in the atmosphere at a rate of ~8 x 10¹² mol yr^-1 (ref. 16). In less than 30 Myr, atmospheric pCO₂ would build up to nearly 0.12 bar, and equatorial ice would become unstable (Fig. 2).” [Full text]