Climates of the Earth and Cryosphere Evolution

Abstract

The interrelationship between the cryosphere and the climate is not always operating on Earth over a scale of billions or millions of years. Indeed, most of the time, the Earth is regulated at temperatures such that no ice sheet exists. Nevertheless, it is very fruitful to understand the conditions where and when ice sheets were triggered during the Earth's history. This paper deals with the paleoclimate and the cryosphere in the last 4.6 Ga and explains the different processes that make the climate of the first 4 billion years warm despite the weaker solar luminosity. We also describe the more recent evolution in the last 65 million years when a global decrease in atmospheric CO 2 from around 4 PAL to 1 PAL was associated with a global cooling (1 PAL present atmospheric level = 280 ppm). It is in this context that the Quaternary occurred characterized by low atmospheric CO 2 and the presence of two perennial ice sheets in Greenland and Antarctica. The last million years are certainly the most documented since direct and reliable CO 2 measurements are available. They are characterized by a complex climate/cryosphere dynamics leading to oscillations between long glacial periods with four ice sheets and shorter ones with only two ice sheets (interglacial). We are currently living in one of those interglacials, generally associated with a CO 2 level of 280 ppm. Presently, anthropogenic activities are seriously perturbing the carbon cycle and the atmospheric CO 2 content and therefore the climate. The last but not least question raised in this paper is to investigate whether the anthropogenic perturbation may lead to a melting of the ice sheets.

The Climates of Earth’s Next Supercontinent: Effects of Tectonics, Rotation Rate, and Insolation

“…No aerosols or Ozone () are included. For the minor species ( and ) this is perhaps the simplest choice given the variability in the past (e.g., Ramstein, 2011), and long‐term uncertainties associated with human generated climate change and the subsequent uncertainties associated with the long‐term evolution of the carbon cycle (e.g., Franck et al., 1999). For the second most abundant species in Earth's atmosphere () the choice is consistent with recent estimates by Ozaki and Reinhard (2021) who set a 1 limit of the longevity of Earth's 21% oxygenated atmosphere of ≈ years.…”

Geological Society of London Scientific Statement: what the geological record tells us about our present and future climate

“…However, even with less solar irradiance 4 billion years ago during the 'Faint Young Sun', liquid (not frozen) water was still present on Earth and climate has generally been warmer than at present (Section 1) (Sagan and Mullen 1972). On the early Earth, an enhanced greenhouse effect is proposed to have compensated for this reduced solar forcing, driven by higher CO 2 and/or methane before 2.5 billion years ago (Ramstein 2011). Since then, increasing solar irradiance has been accompanied by an overall long-term decrease in CO 2 and methane, with variability on shorter timescales.…”

“…the growth of plant biomass on Earth has removed carbon dioxide from the atmosphere and increased atmospheric oxygen concentrations (e.g. Berner and Kothavala 2001;Kasting 2004;Ramstein 2011;Foster et al 2017).…”

Co-evolution of oceans, climate, and the biosphere during the ‘Ordovician Revolution’: A review

“…proposed to account for this supposed anomaly, including a weak early Sun (Ramstein, 2011), 480 high cloud albedo caused by cosmic ray flux (Shaviv and Veizer, 2003), and diminished silicate 481 weathering owing to extensive ice cover invigorating global-ocean circulation and thus leading to improved oxygenation of the deep 508 ocean. It seems possible that a positive feedback between enhanced thermohaline circulation, 509 marine productivity, drawdown of atmospheric pCO 2 , and global cooling may have contributed 510…”