Radiative effects of ozone on the climate of a Snowball Earth

Abstract

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.

Strong modification of stratospheric ozone forcing by cloud and sea-ice adjustments

“…The reduction of high clouds can be attributed to ozoneinduced radiative warming and consequent relative humidity reduction in upper troposphere and lower stratosphere, in accordance with the findings of (Jenkins, 1999;Yang et al, 2012). The sea-ice changes in the Arctic and around the Antarctic are influenced by ozone-induced indirect radiative effects, which are associated with the reduction of downward infrared radiation over the sea-ice edge caused by the insitu decreases of clouds and water vapor, and also the atmospheric cooling .…”

“…There is general reduction in cloud fraction, especially for those high clouds near the tropopause. The decrease in high clouds is associated with a decrease in relative humidity caused by the SOR warming of the upper troposphere and lower stratosphere (Jenkins, 1999;Yang et al, 2012), which is consistent with the significant increase in UTLS cirrus clouds which resulted from in situ ozone depletion found in Nowack et al (2015). This then accounts for the aforementioned negative TOA long-wave cloud radiative effect (Table 1; Fig.…”

Stratospheric Ozone-induced Cloud Radiative Effects on Antarctic Sea Ice

“…This is consistent with the less significant temperature changes in JJA and SON. It has been suggested that the lower-stratospheric warming, due to ozone recovery, enhances static stability and reduces relative humidity in the upper troposphere and near the tropopause, and both contribute to cloud decreases (Jenkins, 1999;Yang et al, 2012;Xia et al, 2016Xia et al, , 2018. From Fig.…”

The Snowball Stratosphere

“…For example, previous work has shown that (1) the tropopause in a snowball is lower (Abbot, ; Pierrehumbert, , ); (2) the Hadley circulation is more intense (Abbot et al, ; Pierrehumbert, , ; Voigt et al, , ), thermally indirect in the annual mean (Abbot and Pierrehumbert, ; Pierrehumbert, , ), and strongly influenced by vertical diffusion of zonal momentum (Voigt et al, , ); and (3) baroclinic eddy dry static energy transport is proportionally more important than in its modern counterpart (Pierrehumbert, , ). The only investigation of the snowball's stratosphere that we have encountered is that of Yang et al (), which examined the radiative effect of ozone on the snowball atmosphere's temperatures and found that reduced ozone leads to a cooler surface. The stratospheric circulation during a snowball, however, has not been investigated in detail.…”