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Estimating Contributions of Sea Ice and Land Snow to Climate Feedback

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In this study, we use the National Center for Atmospheric Research Community Earth System Model to investigate the contribution of sea ice and land snow to the climate sensitivity in response to increased atmospheric carbon dioxide content. We focus on the overall effect arising from the presence or absence of sea ice and/or land snow. We analyze our results in terms of the radiative forcing and climate feedback parameter. We find that the presence of sea ice and land snow decreases the climate feedback parameter (and thus increases climate sensitivity). Adjusted radiative forcing from added carbon dioxide is comparatively less sensitive to the presence of sea ice or land snow. The effect of sea ice on the climate feedback parameter decreases as sea ice cover diminishes at higher CO2 concentration. However, the influence of both sea ice and land snow on the climate feedback parameter remains substantial under the CO2 concentration range considered here (to eight times preindustrial CO2 content). Approximately, one quarter of the effect of sea ice and land snow on the climate feedback parameter is a consequence of the effect of these components on longwave feedback that is mainly associated with cloud change. Polar warming in response to added CO2 is approximately doubled by the presence of sea ice and land snow. Relative to the case in which sea ice and land snow are absent in the model, in response to increased CO2 concentrations, the presence of sea ice and land snow results in an increase in global mean warming by over 40%.
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Estimating Contributions of Sea Ice and Land Snow
to Climate Feedback
Lei Duan
1
, Long Cao
1
, and Ken Caldeira
2
1
Department of Atmospheric Sciences, School of Earth Sciences, Zhejiang University, Hangzhou, China,
2
Department of
Global Ecology, Carnegie Institution, Stanford, CA, USA
Abstract In this study, we use the National Center for Atmospheric Research Community Earth System
Model to investigate the contribution of sea ice and land snow to the climate sensitivity in response to
increased atmospheric carbon dioxide content. We focus on the overall effect arising from the presence or
absence of sea ice and/or land snow. We analyze our results in terms of the radiative forcing and climate
feedback parameter. We nd that the presence of sea ice and land snow decreases the climate feedback
parameter (and thus increases climate sensitivity). Adjusted radiative forcing from added carbon dioxide is
comparatively less sensitive to the presence of sea ice or land snow. The effect of sea ice on the climate
feedback parameter decreases as sea ice cover diminishes at higher CO
2
concentration. However, the
inuence of both sea ice and land snow on the climate feedback parameter remains substantial under the
CO
2
concentration range considered here (to eight times preindustrial CO
2
content). Approximately, one
quarter of the effect of sea ice and land snow on the climate feedback parameter is a consequence of the effect
of these components on longwave feedback that is mainly associated with cloud change. Polar warming
in response to added CO
2
is approximately doubled by the presence of sea ice and land snow. Relative to the
case in which sea ice and land snow are absent in the model, in response to increased CO
2
concentrations,
the presence of sea ice and land snow results in an increase in global mean warming by over 40%.
Plain Language Summary Sea ice and land snow are two crucial components that affect the
climate response to external forcings. Feedbacks between ice/snow and climate change cause amplied
surface warming in high latitudes. In this study, we use a climate model to estimate the contribution of sea
ice and land snow to climate change in response to increased CO
2
concentrations. We compare the climate
response to increased CO
2
between the simulations with sea ice and/or land snow and the simulations
without them. We show that the existence of sea ice and land snow substantially amplies the global
temperature response to increased CO
2
with sea ice having a stronger effect than land snow. Under higher
CO
2
levels, the effect of sea ice diminishes more rapidly than does the effect of land snow. About one
quarter of the total climate feedback from sea ice and land snow is associated with the change in longwave
radiation. Also we show that the effect of sea ice and land snow on the sensitivity of topofatmosphere
net energy ux to the global mean temperature change is approximately additive.
1. Introduction
Observations and modeling studies have recognized that the global warming from increased atmospheric
CO
2
concentrations is amplied in polar regions (e.g., Bekryaev et al., 2010; Bromwich et al., 2013;
Chapman & Walsh, 2007; Manabe et al., 1991; Manabe & Stouffer, 1980; Meehl et al., 2007; Pithan &
Mauritsen, 2014; Serreze & Francis, 2006; Solomon, 2006). Sea ice and land snow are two important
components contributing to substantial warming in middle and high latitudes, primarily from their surface
albedo feedback and the insulation feedback (Caldeira & Cvijanovic, 2014; Cess et al., 1991; Hall, 2004;
Holland et al., 2001; Holland & Bitz, 2003; Screen & Simmonds, 2010; Serreze et al., 2009; Stroeve et al.,
2012; Vavrus, 2007; Winton, 2006; Zhang, 2005). For example, sea ice and land snow retreats expose less
reective land and ocean surface, increasing the absorption of solar insolation. The presence of sea ice
and land snow inhibits the energy exchange between atmosphere and surface. Other factors also contribute
to highlatitude amplication of the temperature change, including the Planck feedback, changes in water
vapor content, atmospheric and oceanic heat transport, and cloud fraction in response to the imposed
forcing and the seaice and land snow decline (e.g., Kay et al., 2012; Mahlstein & Knutti, 2011; Overland
& Wang, 2010; Södergren et al., 2018; Solomon, 2006; Taylor et al., 2013).
DUAN ET AL. 199
RESEARCH ARTICLE
10.1029/2018JD029093
Key Points:
We use NCAR CESM to investigate
the overall contribution of sea ice
and land snow to climate feedback
to increased carbon dioxide content
Sea ice and land snow lead to
substantial increases in polar
warming to increased CO
2
content
with sea ice playing a more
important role
The presence of sea ice and land
snow decreases the climate feedback
parameter with about one quarter of
the effect from longwave feedback
Supporting Information:
Supporting Information S1
Correspondence to:
L. Cao,
longcao@zju.edu.cn
Citation:
Duan, L., Cao, L., & Caldeira, K. (2019).
Estimating contributions of sea ice and
land snow to climate feedback. Journal
of Geophysical Research: Atmospheres,
124, 199208. https://doi.org/10.1029/
2018JD029093
Received 31 MAY 2018
Accepted 14 DEC 2018
Accepted article online 7 JAN 2019
Published online 15 JAN 2019
©2019. American Geophysical Union.
All Rights Reserved.
... The issue of CO2 effects on global warming of 371 the land and ocean is established. This situation is contrasted with the studies by Duan et al. (2019), which allows validating the vulnerability of sea ice and land snow when exposed to the effects of increased atmospheric CO2. ...
... Reducing surface albedo causes greater absorption of solar radiation that warms the surface and drives additional sea ice and snow melt. Studies estimate that the sea ice-snow albedo feedback is responsible for 30-60% of the total CO 2 -induced Arctic warming (Dickinson et al., 1987;Hall 2004;Taylor et al., 2013;Boeke and Taylor 2018;Duan et al., 2019) and is the largest local Arctic feedback (Taylor et al., 2013;Yoshimori et al., 2014;Goosse et al., 2018). Multi-centennial climate simulations show that Arctic warming slows after most of the sea ice melts, further highlighting the importance of sea ice (Bintanja and van der Linden 2013;Dai et al., 2019). ...
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