ArticlePublisher preview available

Estimating Contributions of Sea Ice and Land Snow to Climate Feedback

DOI:10.1029/2018JD029093
Authors:
Duan Lei at Carnegie Institution for Science
Duan Lei
Long Cao at Zhejiang University
Long Cao
Ken Caldeira at Gates Ventures LLC
Ken Caldeira
  • Gates Ventures LLC
Read publisher preview
Download citation
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

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%.
Model‐simulated global mean surface temperature change for “None”, “Ice”, “Snow”, and “Both” simulations under various CO2 levels. All results are calculated using the last 60‐year results of 100‐year slab‐ocean simulations with uncertainty represented by one standard error.
Model‐simulated global mean surface temperature change for “None”, “Ice”, “Snow”, and “Both” simulations under various CO2 levels. All results are calculated using the last 60‐year results of 100‐year slab‐ocean simulations with uncertainty represented by one standard error.
… 
Model‐simulated changes in zonal distribution of surface air temperature for “None,” “Ice,” “Snow,” and “Both” simulations under 4 × CO2 relative to the corresponding 1 × CO2 case with the same sea ice and snow treatment. All results are calculated from the last 60‐year simulations of 100‐year slab‐ocean simulations. Ice and snow responses amplify the temperature response to increased atmospheric CO2, especially in polar regions.
Model‐simulated changes in zonal distribution of surface air temperature for “None,” “Ice,” “Snow,” and “Both” simulations under 4 × CO2 relative to the corresponding 1 × CO2 case with the same sea ice and snow treatment. All results are calculated from the last 60‐year simulations of 100‐year slab‐ocean simulations. Ice and snow responses amplify the temperature response to increased atmospheric CO2, especially in polar regions.
… 
Gregory regressions of top‐of‐atmosphere (TOA) (a) net radiative flux (positive downward), (b) net shortwave, and (c) net longwave radiation versus global mean surface temperature change for “None,” “Ice,” “Snow,” and “Both” simulations under 4 × CO2 simulations relative to the corresponding 1 × CO2 case with the same sea ice and snow treatment. The 100‐year slab‐ocean simulations with two additional 10‐year simulations with slightly altered initial condition are used for regression. Results for the slope (climate feedback parameter) and vertical axis intercepts (adjusted radiative forcing) of this regression are shown in Table 2. Panels for other CO2 levels are shown in supporting information Figure S4. The primary influence of ice and snow on the climate feedback parameter is through the shortwave component.
Gregory regressions of top‐of‐atmosphere (TOA) (a) net radiative flux (positive downward), (b) net shortwave, and (c) net longwave radiation versus global mean surface temperature change for “None,” “Ice,” “Snow,” and “Both” simulations under 4 × CO2 simulations relative to the corresponding 1 × CO2 case with the same sea ice and snow treatment. The 100‐year slab‐ocean simulations with two additional 10‐year simulations with slightly altered initial condition are used for regression. Results for the slope (climate feedback parameter) and vertical axis intercepts (adjusted radiative forcing) of this regression are shown in Table 2. Panels for other CO2 levels are shown in supporting information Figure S4. The primary influence of ice and snow on the climate feedback parameter is through the shortwave component.
… 
Contributions of the sea ice and/or land snow components to the climate feedback parameter for “Both,” “Ice,” and “Snow” simulations relative to the “None” simulations. The “Ice” + “Snow” bar represents the height of “Ice” bar stacked on top of the “Snow” bar. The comparison between “‘Both” and “Ice + Snow” shows that the effects of ice and snow on the climate feedback parameter are approximately additive.
Contributions of the sea ice and/or land snow components to the climate feedback parameter for “Both,” “Ice,” and “Snow” simulations relative to the “None” simulations. The “Ice” + “Snow” bar represents the height of “Ice” bar stacked on top of the “Snow” bar. The comparison between “‘Both” and “Ice + Snow” shows that the effects of ice and snow on the climate feedback parameter are approximately additive.
… 
Model‐simulated sea ice area and land snow area as a function of global mean surface temperature for “None,” “Ice,” “Snow,” and “Both” simulations at various CO2 levels. All results are calculated from the last 60‐year simulations of 100‐year slab‐ocean simulations. The sea‐ice and land‐snow areas are calculated by multiplying the sea‐ice and land‐snow fraction in each grid cell with areas of that grid and then integrating over the globe.
+1
Model‐simulated sea ice area and land snow area as a function of global mean surface temperature for “None,” “Ice,” “Snow,” and “Both” simulations at various CO2 levels. All results are calculated from the last 60‐year simulations of 100‐year slab‐ocean simulations. The sea‐ice and land‐snow areas are calculated by multiplying the sea‐ice and land‐snow fraction in each grid cell with areas of that grid and then integrating over the globe.
… 
Figures - available from: Journal of Geophysical Research Atmospheres
This content is subject to copyright. Terms and conditions apply.
  • A preview of this full-text is provided by Wiley.
  • Learn more
Preview content only
Content available from Journal of Geophysical Research Atmospheres
This content is subject to copyright. Terms and conditions apply.
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 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 CO
2
concentration. However, the
influence 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 amplified
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 amplifies 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 top‐of‐atmosphere
net energy flux 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 amplified 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
reflective 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 high‐latitude amplification 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 sea‐ice 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, 199–208. 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.
... 5) increases mean annual temperatures by up to 5 °C in North America and Eurasia (Varvus 2007) and 0.84-0.97 °C globally (Vavrus 2007;Duan et al. 2019). For our sample, removing the 1972-2008 mean value for snow cover for the 215 cells that have a mean greater than zero raises their average temperature by about 0.70 °C. ...
... Climate models generate keen insights into anthropogenic climate change by running carefully controlled experiments, which are not possible in the real world. For example, the effect of snow cover on temperature is quantified by experiments that convert all precipitation to a liquid form (Vavrus 2007;Duan et al. 2019). ...
An empirical estimate for the snow albedo feedback effect
Article
Full-text available
We estimate snow albedo feedback effects of anthropogenic increases in global radiative forcing, which includes carbon dioxide, methane, nitrous oxide, CFC11, CFC12, black carbon, anthropogenic sulfur emissions, total solar irradiance, and local sulfur emissions by compiling annual observations (1972–2008) for radiative forcing, temperature, snow cover, sulfur emissions, and various teleconnections for 255 \({5}^{^\circ }\times {5}^{^\circ }\) grid cells in the Northern Hemisphere. Panel DOLS estimates of the long-run relations indicate that the effect of radiative forcing on temperature increases with latitude (consistent with polar amplification), eliminating snow cover increases local temperature by about 2.8 °C, and a 1 °C temperature increase reduces snow cover by about 1%. These values create a snow albedo feedback (SAF) that amplifies the temperature increase of higher forcing by about 3.4% relative to its direct effect while an increase in sulfur emissions increases the temperature reduction by about 0.4% relative to its direct effect. The 3.4% SAF is smaller than values generated by process-based climate models and may be associated with the empirical estimates for snowmelt sensitivity \({\Delta S}_{c}/\Delta {T}_{s}\). To narrow estimates for the SAF from climate models, we conclude with suggestions for a new experimental design that controls for the simultaneous relation between temperature and snow cover.
View
... 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. ...
View
... 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). ...
Process Drivers, Inter-Model Spread, and the Path Forward: A Review of Amplified Arctic Warming
Article
Full-text available
  • Feb 2022
Arctic amplification (AA) is a coupled atmosphere-sea ice-ocean process. This understanding has evolved from the early concept of AA, as a consequence of snow-ice line progressions, through more than a century of research that has clarified the relevant processes and driving mechanisms of AA. The predictions made by early modeling studies, namely the fall/winter maximum, bottom-heavy structure, the prominence of surface albedo feedback, and the importance of stable stratification have withstood the scrutiny of multi-decadal observations and more complex models. Yet, the uncertainty in Arctic climate projections is larger than in any other region of the planet, making the assessment of high-impact, near-term regional changes difficult or impossible. Reducing this large spread in Arctic climate projections requires a quantitative process understanding. This manuscript aims to build such an understanding by synthesizing current knowledge of AA and to produce a set of recommendations to guide future research. It briefly reviews the history of AA science, summarizes observed Arctic changes, discusses modeling approaches and feedback diagnostics, and assesses the current understanding of the most relevant feedbacks to AA. These sections culminate in a conceptual model of the fundamental physical mechanisms causing AA and a collection of recommendations to accelerate progress towards reduced uncertainty in Arctic climate projections. Our conceptual model highlights the need to account for local feedback and remote process interactions within the context of the annual cycle to constrain projected AA. We recommend raising the priority of Arctic climate sensitivity research, improving the accuracy of Arctic surface energy budget observations, rethinking climate feedback definitions, coordinating new model experiments and intercomparisons, and further investigating the role of episodic variability in AA.
View
... The enhanced ocean-to-atmosphere energy exchange in fall and winter, which acts to warm the near-surface atmosphere, is now recognized to be of primary importance to AA (e.g., Screen To summarize, there is considerable evidence that surface albedo feedbacks -and other feedbacks associated with the loss of sea ice and snow cover in a warming climatemake significant contributions to AA. It is worth noting, however, that polar-amplified warming has still been simulated in climate models even when surface albedo feedbacks (Hall 2004, Graversen and Wang 2009, Lu and Cai 2010, Graversen et al 2014 and all sea ice-and/or snow cover-related feedbacks (Schneider et al 1997, Schneider et al 1999, Alexeev 2003, Alexeev et al 2005, Duan et al 2019 have been eliminated (e.g., by fixing the surface albedo). This suggests that other processes are capable of producing AA, even in the absence of any changes in surface albedo and/or sea ice/snow cover. ...
Arctic amplification of climate change: A review of underlying mechanisms
Article
Full-text available
Arctic amplification (AA) - referring to the enhancement of near-surface air temperature change over the Arctic relative to lower latitudes - is a prominent feature of climate change with important impacts on human and natural systems. In this review, we synthesize current understanding of the underlying physical mechanisms that can give rise to AA. These mechanisms include both local feedbacks and changes in poleward energy transport. Temperature and sea ice-related feedbacks are especially important for AA, since they are significantly more positive over the Arctic than at lower latitudes. Changes in energy transport by the atmosphere and ocean can also contribute to AA. These energy transport changes are tightly coupled with local feedbacks, and thus their respective contributions to AA should not be considered in isolation. It is here emphasized that the feedbacks and energy transport changes that give rise to AA are sensitively dependent on the state of the climate system itself. This implies that changes in the climate state will lead to changes in the strength of AA, with implications for past and future climate change.
View
Comment on “Climate consequences of hydrogen emissions” by Ocko and Hamburg (2022)
Article
Full-text available
In this commentary, we provide additional context for Ocko and Hamburg (2022) related to the climate consequences of replacing fossil fuels with clean hydrogen alternatives. We first provide a tutorial for the derivations of underlying differential equations that describe the radiative forcing of hydrogen emissions, which differ slightly from equations relied on by previous studies. Ocko and Hamburg (2022) defined a metric based on time-integrated radiative forcing from continuous emissions. To complement their analysis, we further present results for temperature and radiative forcing over the next centuries for unit pulse and continuous emissions scenarios. Our results are qualitatively consistent with previous studies, including Ocko and Hamburg (2022). Our results clearly show that for the same quantity of emissions, hydrogen shows a consistently smaller climate impact than methane. As with other short-lived species, the radiative forcing from a continuous emission of hydrogen is proportional to emission rates, whereas the radiative forcing from a continuous emission of carbon dioxide is closely related to cumulative emissions. After a cessation of hydrogen emissions, the Earth cools rapidly, whereas after a cessation of carbon dioxide emissions, the Earth continues to warm somewhat and remains warm for many centuries. Regardless, our results support the conclusion of Ocko and Hamburg (2022) that, if methane were a feedstock for hydrogen production, any possible near-term consequences will depend primarily on methane leakage and secondarily on hydrogen leakage.
View
Comment on “Climate consequences of hydrogen emissions” by Ocko and Hamburg (2022)
Preprint
Full-text available
  • Dec 2022
In this commentary, we provide additional context for Ocko and Hamburg (2022) related to the climate consequences of replacing fossil fuels with clean hydrogen alternatives. To develop a better understanding of the climate impact from atmospheric hydrogen additions, we first provide a step-by-step tutorial for the derivations of underlying differential equations that describe radiative forcing of hydrogen emissions, which differ slightly from equations relied on by previous studies. Ocko and Hamburg (2022) used a time-integrated metric on radiative forcing and considered a continuous emission scenario, while we present both the time-evolving radiative forcing and global mean temperature response results under a unit pulse and continuous emissions scenarios. Our analysis covers timescales of 500 years and results on short-term timescales (e.g., 20 years) are qualitatively consistent with previous studies. Some qualitative results are clear: radiative forcing from hydrogen emission is smaller compared to the same quantity of methane emission, both of which decay with time and show less long-term influence than carbon dioxide. On the time scale of a few decades, the radiative forcing from a continuous emission of hydrogen or methane is proportional to emission rates, whereas the radiative forcing from a continuous emission of carbon dioxide is closely related to cumulative emissions. After a cessation of clean hydrogen consumption, the earth cools rapidly, whereas after a cessation of carbon dioxide emissions, the earth continues to warm somewhat and remains warm for many centuries. These longer-term differences may be important to consider in a policy context. Hydrogen leakage has the potential to reduce near-term climate benefits of hydrogen use, but methane is likely to play a more substantial role. In our analysis, consideration of methane emission associated with fossil fuel combustion is a critical factor for determining the relative short-term climate benefits of clean hydrogen alternatives. In the main cases, consideration of methane leakage substantially increases the climate impacts of fossil fuels and could result in net climate benefits for blue hydrogen even in the near-term. Regardless, our results support the conclusion of Ocko and Hamburg (2022) that, if methane were a feedstock for hydrogen production, any possible near-term consequences will depend critically on the issue of methane leakage.
View
Current knowledge and uncertainties associated with the Arctic greenhouse gas budget
Chapter
  • Jan 2022
•The Arctic is continuing to warm faster than any other region on Earth, but key uncertainties remain in our knowledge of the Arctic carbon cycle. •We review the most current knowledge pertaining to estimates of arctic greenhouse gas components and discuss uncertainties associated with these measurements and models. •While the Arctic Ocean is consistently estimated as a carbon sink, we have yet to reach an agreement on either the magnitude or the sign of the arctic terrestrial carbon budget. •Much of the uncertainty in the arctic carbon budget is related to the extent of the amount of carbon released as permafrost thaws, the magnitude of shoulder season and winter ecosystem respiration, and the impact of rising temperature and atmospheric [CO2] on plant growth. •We cannot count on the Arctic to store as much carbon as it has in the past, and evidence indicates it will likely store much less.
View
View
Process drivers, inter-model spread, and the path forward: A review of amplified Arctic warming
Preprint
  • Sep 2021
Arctic amplification (AA) is a coupled atmosphere-sea ice-ocean process. This understanding has evolved from the early concept of AA, as a consequence of snow-ice line progressions, through more than a century of research that has clarified the relevant processes and driving mechanisms of AA. The predictions made by early modeling studies, namely the fall/winter maximum, bottom-heavy structure, the prominence of surface albedo feedback, and the importance of stable stratification have withstood the scrutiny of multi-decadal observations and more complex models. Yet, the uncertainty in Arctic climate projections is larger than in any other region of the planet, making assessment of high-impact, near-term regional changes difficult or impossible. Reducing this large spread in Arctic climate projections requires a quantitative process understanding. This manuscript aims to build such understanding by synthesizing current knowledge of AA and to produce a set of recommendations to guide future research. It briefly reviews the history of AA science, summarizes observed Arctic changes, discusses modeling approaches and feedback diagnostics, and assesses the current understanding of the most relevant feedbacks to AA. These sections culminate in a conceptual model of the fundamental physical mechanisms causing AA and a collection of recommendations to accelerate progress towards reduced uncertainty in Arctic climate projections. Our conceptual model highlights the need to account for local feedback and remote process interactions, specifically the water vapor triple effect, within the context of the annual cycle to constrain projected AA. We recommend raising the priority of Arctic climate sensitivity research, improving the accuracy of Arctic surface energy budget observations, rethinking climate feedback definitions, coordinating new model experiments and intercomparisons, and pursuing the role of episodic variability in AA as a research focus area.
View
CLIMATE-FRAGILITY RISK BRIEF: THE ARCTIC
Research
Full-text available
  • Jul 2021
Climate change is manifesting in the Arctic three times faster than the global rate of change. These changes present both risks and opportunities. Without proper risk mitigation and climate adaptation efforts, however, the opportunities will likely be undermined by the destabilizing, compounding effects of runaway climate change.
View
An energy balance model exploration of the impacts of interactions between surface albedo, cloud cover and water vapor on polar amplification
Article
Full-text available
We examine the effects of non-linear interactions between surface albedo, water vapor and cloud cover (referred to as climate variables) on amplified warming of the polar regions, using a new energy balance model. Our simulations show that the sum of the contributions to surface temperature changes due to any variable considered in isolation is smaller than the temperature changes from coupled feedback simulations. This non-linearity is strongest when all three climate variables are allowed to interact. Surface albedo appears to be the strongest driver of this non-linear behavior, followed by water vapor and clouds. This is because increases in longwave radiation absorbed by the surface, related to increases in water vapor and clouds, and increases in surface absorbed shortwave radiation caused by a decrease in surface albedo, amplify each other. Furthermore, our results corroborate previous findings that while increases in cloud cover and water vapor, along with the greenhouse effect itself, warm the polar regions, water vapor also significantly warms equatorial regions, which reduces polar amplification. Changes in surface albedo drive large changes in absorption of incoming shortwave radiation, thereby enhancing surface warming. Unlike high latitudes, surface albedo change at low latitudes are more constrained. Interactions between surface albedo, water vapor and clouds drive larger increases in temperatures in the polar regions compared to low latitudes. This is in spite of the fact that, due to a forcing, cloud cover increases at high latitudes and decreases in low latitudes, and that water vapor significantly enhances warming at low latitudes.
View
Estimating the contribution of sea ice response to climate sensitivity in a climate model
Article
Full-text available
  • Jan 2014
The response of sea ice to climate change affects Earth's radiative properties in ways that contribute to yet more climate change. Here, a configuration of the Community Earth System Model, version 1.0.4 (CESM1.0.4), with a slab ocean model and a thermodynamic-dynamic sea ice model is used to investigate the overall contribution to climate sensitivity of feedbacks associated with the sea ice loss. In simulations in which sea ice is not present and ocean temperatures are allowed to fall below freezing, the climate feedback parameter averages ~1.31Wm-2K-1; the value obtained for control simulations with active sea ice is ~1.05Wm-2K-1, indicating that, in this configuration of CESM1.0.4, sea ice response accounts for ~20% of climate sensitivity to an imposed change in radiative forcing. In this model, the effect of sea ice response on the longwave climate feedback parameter is nearly half as important as its effect on the shortwave climate feedback parameter. Further, it is shown that the strength of the overall sea ice feedback can be related to 1) the sensitivity of sea ice area to changes in temperature and 2) the sensitivity of sea ice radiative forcing to changes in sea ice area. An alternative method of disabling sea ice response leads to similar conclusions. It is estimated that the presence of sea ice in the preindustrial control simulation has a climate effect equivalent to ~3Wm-2 of radiative forcing.
View
Recent Arctic amplification and extreme mid-latitude weather
Article
Full-text available
  • Aug 2014
The Arctic region has warmed more than twice as fast as the global average - a phenomenon known as Arctic amplification. The rapid Arctic warming has contributed to dramatic melting of Arctic sea ice and spring snow cover, at a pace greater than that simulated by climate models. These profound changes to the Arctic system have coincided with a period of ostensibly more frequent extreme weather events across the Northern Hemisphere mid-latitudes, including severe winters. The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways linking Arctic amplification to mid-latitude weather: changes in storm tracks, the jet stream, and planetary waves and their associated energy propagation. Through changes in these key atmospheric features, it is possible, in principle, for sea ice and snow cover to jointly influence mid-latitude weather. However, because of incomplete knowledge of how high-latitude climate change influences these phenomena, combined with sparse and short data records, and imperfect models, large uncertainties regarding the magnitude of such an influence remain. We conclude that improved process understanding, sustained and additional Arctic observations, and better coordinated modelling studies will be needed to advance our understanding of the influences on mid-latitude weather and extreme events.
View
Atmospheric impacts of sea ice decline in CO2 induced global warming
Article
Full-text available
  • Mar 2015
Changes in sea ice cover have important consequences for both Earth’s energy budget and atmospheric dynamics. Sea ice acts as a positive feedback in the climate system, amplifying effects of radiative forcing while also affecting the meridional and interhemispheric temperature gradients that can impact mid- and low latitude atmospheric circulation. In this study, we partition and evaluate the effects of changing sea ice cover on global warming using a set of simulations with active and suppressed sea ice response. Two aspects of CO2-induced sea ice changes are investigated: (1) the effect of changing sea ice cover on global and local temperature changes; and (2) the impact of sea ice loss on atmospheric circulation and extreme weather events. We find that in the absence of sea ice decline, global temperature response decreases by 21-37 %, depending on the sea ice treatment and the CO2 forcing applied. Weakened global warming in the absence of changes in sea ice cover is not only due to a decreased high latitude warming but is also a consequence of a weaker tropical warming. In the northern midlatitudes, sea ice decline affects the magnitude and sign of zonal wind response to global warming in the winter and autumn seasons. Presence or absence of sea ice cover impacts the intensity and frequency of winter extreme precipitation and temperature events (temperature minima, number of heavy precipitation days and number of ice days). For some of the analyzed extreme weather indices, the difference between the responses with and without sea ice decline is eliminated when taking into account the amplifying effect of sea ice loss on hemispheric warming. However, in other cases, we find the influence of higher order factors, exerting weaker but opposing effects than those expected from the global temperature increase.
View
Supplementary Information for: Central West Antarctica among the most rapidly warming regions on Earth
Article
Full-text available
  • Feb 2013
This Supplementary Information contains: 1. Supplementary Discussion 1.1. Byrd 1980s warming and atmospheric circulation over the Ross-Amundsen Seas 2. Supplementary Methods 2.1. Background on the temperature observations from Byrd Station/AWS 2.1.1. Historical background 2.1.2. Corrections to Byrd AWS observations from 1989–01/2011 2.1.3. Potential sources of error in the AWS observations 2.2. Details on the infilling method 2.2.1. Infilling of the Byrd record: 1979–2011 period (alternative method) 2.2.2. ERA-Interim forecast versus analysis temperatures 2.3. Uncertainty calculation 2.3.1 Uncertainties of the reconstructed temperatures 2.3.2 Uncertainties of the temperature trends 3. Supplementary Material 3.1. Global reanalysis data 3.2. Global temperature data 4. References 5. Supplementary Figures 5.1. Figures related to the main text discussion 5.2. Figures related to the infilling method 6. Supplementary Tables
View
Comparison of surface albedo feedback in climate models and observations
Article
Full-text available
and ice albedo feedback plays an important role in the greater warming of the Arctic compared to the tropics. Previous work has estimated the observed Northern Hemisphere cryosphere feedback, but there have been no estimates of surface albedo feedback from observations globally. Here we compare the zonal mean surface albedo feedback from satellite data sets with that from eleven ocean-atmosphere coupled climate models for both climate change and the seasonal cycle. Differences between observed data sets make it difficult to constrain models. Nevertheless, we find that climate change Northern Hemisphere extratropical feedback is considerably higher for observations (potentially 3.1 ± 1.3 W m-2 K-1) than models (0.4-1.2 W m-2 K-1), whereas the seasonal cycle feedback is similar in observations and models, casting doubt on the ability of the seasonal cycle to accurately predict the climate change feedback. Observed Antarctic sea ice feedback is strongly positive in the seasonal cycle and similar to models.
View
The Dependence of Global Cloud and Lapse Rate Feedbacks on the Spatial Structure of Tropical Pacific Warming
Article
  • Oct 2017
An atmospheric general circulation model (AGCM) is forced with patterns of observed sea surface temperature (SST) change and those output from atmosphere-ocean GCM (AOGCM) climate change simulations to demonstrate a strong dependence of climate feedback on the spatial structure of surface temperature change. Cloud and lapse rate feedbacks are found to vary the most, depending strongly on the pattern of tropical Pacific SST change. When warming is focused in the southeast tropical Pacific-a region of climatological subsidence and extensive marine low cloud cover-warming reduces the lower-tropospheric stability (LTS) and low cloud cover but is largely trapped under an inversion and hence has little remote effect. The net result is a relatively weak negative lapse rate feedback and a large positive cloud feedback. In contrast, when warming is weak in the southeast tropical Pacific and enhanced in the west tropical Pacific-a strong convective region-warming is efficiently transported throughout the free troposphere. The increased atmospheric stability results in a strong negative lapse rate feedback and increases the LTS in low cloud regions, resulting in a low cloud feedback of weak magnitude. These mechanisms help explain why climate feedback and sensitivity change on multidecadal time scales in AOGCM abrupt4xCO2 simulations and are different from those seen in AGCM experiments forced with observed historical SST changes. From the physical understanding developed here, one should expect unusually negative radiative feedbacks and low effective climate sensitivities to be diagnosed from real-world variations in radiative fluxes and temperature over decades in which the eastern Pacific has lacked warming.
View
A Decomposition of Feedback Contributions to Polar Warming Amplification
Article
  • Sep 2013
Polar surface temperatures are expected to warm 2-3 times faster than the global-mean surface temperature: a phenomenon referred to as polar warming amplification. Therefore, understanding the individual process contributions to the polar warming is critical to understanding global climate sensitivity. The Coupled Feedback Response Analysis Method (CFRAM) is applied to decompose the annual- and zonal-mean vertical temperature response within a transient 1% yr(-1) CO2 increase simulation of the NCAR Community Climate System Model, version 4 (CCSM4), into individual radiative and nonradiative climate feedback process contributions. The total transient annual-mean polar warming amplification (amplification factor) at the time of CO2 doubling is +2.12 (2.3) and +0.94 K (1.6) in the Northern and Southern Hemisphere, respectively. Surface albedo feedback is the largest contributor to the annual-mean polar warming amplification accounting for +1.82 and +1.04 K in the Northern and Southern Hemisphere, respectively. Net cloud feedback is found to be the second largest contributor to polar warming amplification (about +0.38 K in both hemispheres) and is driven by the enhanced downward longwave radiation to the surface resulting from increases in low polar water cloud. The external forcing and atmospheric dynamic transport also contribute positively to polar warming amplification: +0.29 and +0.32 K, respectively. Water vapor feedback contributes negatively to polar warming amplification because its induced surface warming is stronger in low latitudes. Ocean heat transport storage and surface turbulent flux feedbacks also contribute negatively to polar warming amplification. Ocean heat transport and storage terms play an important role in reducing the warming over the Southern Ocean and Northern Atlantic Ocean.
View
Exploring trends in Northern Hemisphere blocking
Article
Observed blocking trends are diagnosed to test the hypothesis that recent Arctic warming and sea ice loss has increased the likelihood of blocking over the Northern Hemisphere. To ensure robust results, we diagnose blocking using three unique blocking identification methods from the literature, each applied to four different reanalyses. No clear hemispheric increase in blocking is found for any blocking index, and while seasonal increases and decreases are found for specific isolated regions and time periods, there is no instance where all three methods agree on a robust trend. Blocking is shown to exhibit large interannual and decadal variability, highlighting the difficulty in separating any potentially forced response from natural variability.
View
Global Warming and Winter Weather
Article
In mid-January, a lobe of the polar vortex sagged southward over the central and eastern United States. All-time low temperature records for the calendar date were set at O'Hare Airport in Chicago [−16°F (−27°C), 6 January], at Central Park in New York [4°F (−15.6°C), 7 January], and at
View