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Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global climate change.^[1] For instance, at higher latitudes, warmer temperatures melt the ice sheets.^[2] However, if warm temperatures decrease the ice cover and the area is replaced by water or land, the albedo would decrease. This increases the amount of solar energy absorbed, leading to more warming.^[3] The change in albedo acts to reinforce the initial alteration in ice area leading to more warming. Warming tends to decrease ice cover and hence decrease the albedo, increasing the amount of solar energy absorbed and leading to more warming. In the geologically recent past, the ice–albedo positive feedback has played a major role in the advances and retreats of the Pleistocene (~2.6 Ma to ~10 ka ago) ice sheets.^[4] Inversely, cooler temperatures increase ice, which increases albedo, leading to more cooling.

Significance

Current

Snow– and ice–albedo feedback have a substantial effect on regional temperatures. In particular, the presence of ice cover makes the North Pole and the South Pole colder than they would have been without it. Consequently, recent Arctic sea ice decline is one of the primary factors behind the Arctic warming nearly four times faster than the global average since 1979 (the year when continous satellite readings of the Arctic sea ice began). ^[5], in a phenomenon known as Arctic amplification. Modelling studies show that strong Arctic amplification only occurs during the months when significant sea ice loss occurs, and that it largely disappears when the simulated ice cover is held fixed. ^[6] Conversely, the high stability of ice cover in Antarctica, where the thickness of the East Antarctic ice sheet allows it to rise nearly 4 km above the sea level, means that this continent has not experienced any net warming over the past seven decades^[7]: ice loss in the Antarctic and its contribution to sea level rise is instead driven entirely by the warming of the Southern Ocean, which had absorbed 35–43% of the total heat taken up by all oceans between 1970 and 2017. ^[8]

Ice-albedo feedback also has a smaller, but still notable effect on the global temperatures. Arctic ice decline between 1979 and 2011 is estimated to have been responsible for 0.21 watts per square meter (W/m²) of radiative forcing, which is equivalent to a quarter of radiative forcing from CO2^[9] increases over the same period. When compared to cumulative increases in greenhouse gas radiative forcing since the start of the Industrial Revolution, it is equivalent to the estimated 2019 radiative forcing from nitrous oxide (0.21 W/m²), nearly half of 2019 radiative forcing from methane (0.54 W/m²) and 10% of the cumulative CO2 increase (2.16 W/m²). ^[10]

Future

The impact of ice-albedo feedback on temperature will intensify in the future as the Arctic sea ice decline is projected to become more pronounced, with a likely near-complete loss of sea ice cover (falling below 1 million km²) at the end of the Arctic summer in September at least once before 2050 under all climate change scenarios^[11], and around 2035 under the scenario of continually accelerating greenhouse gas emissions.^[12] Since September marks the end of the Arctic summer, it also represents the nadir of sea ice cover in the present climate, with an annual recovery process beginning in the Arctic winter. Consecutive ice-free Septembers are considered highly unlikely in the near future, but their frequency will increase with greater levels of global warming: a 2018 paper estimated that an ice-free September would occur once in every 40 years under a warming of 1.5 degrees Celsius, but once in every 8 years under 2 degrees and once in every 1.5 years under 3 degrees. ^[13] This means that the loss of Arctic sea ice during September or earlier in the summer would not be irreversible, and in the scenarios where global warming begins to reverse, its annual frequency would begin to go down as well. As such, it is not considered one of the tipping points in the climate system.

Notably, while the loss of sea ice cover in September would be a historic event with significant implications for Arctic wildlife like polar bears, its impact on the ice-albedo feedback is relatively limited, as the total amount of solar energy received by the Arctic in September already very low. On the other hand, even a relatively small reduction in June sea ice extent would have a far greater effect, since June represents the peak of the Arctic summer and the most intense transfer of solar energy^[9]. CMIP5 models estimate that a total loss of Arctic sea ice cover from June to September would increase the global temperatures by 0.19 degrees Celsius, with a range of 0.16–0.21°C, while the regional temperatures would increase by over 1.5 degrees. This estimate includes not just the ice-albedo feedback itself, but also its second-order effects such the impact of such sea ice loss on lapse rate feedback, the changes in water vapor concentrations and regional cloud feedbacks.^[14] Since these calculations are are already part of every CMIP5 and CMIP6 model^[15], they are also included in their warming projections under every climate change pathway, and do not represent a source of "additional" warming on top of their existing projections.

Very high levels of global warming could prevent Arctic sea ice from reforming during the Arctic winter. Unlike an ice-free summer, this ice-free Arctic winter may represent an irreversible tipping point. It is most likely to occur at around 6.3 degrees Celsius, though it could potentially occur as early as 4.5°C or as late as 8.7°C.^[16] ^[17] While the Arctic sea ice would be gone for an entire year, it would only have an impact on the ice-albedo feedback during the months where sunlight is received by the Arctic - i.e. from March to September. This is estimated to have the impact equivalent to a trillion tons of CO2 emissions^[9] - around 40% of the 2.39 trillion tons of cumulative emissions between 1850 and 2019^[18], and would have a global warming impact of 0.6 degrees, with a regional warming between 0.6 and 1.2 degrees.^[17]

As land ice melts and causes eustatic sea level rise, it can also potentially induce earthquakes^[19] as a result of post-glacial rebound, which further disrupts glaciers and ice shelves.

Snowball Earth

The runaway ice–albedo feedback was also important for the Snowball Earth. Geological evidence show glaciers near the equator,^[20] and models have suggested the ice–albedo feedback played a role. As more ice formed, more of the incoming solar radiation was reflected back into space, causing temperatures on Earth to drop. Whether the Earth was a complete solid snowball (completely frozen over), or a slush ball with a thin equatorial band of water still remains debated,^[21] but the ice–albedo feedback mechanism remains important for both cases.

Ice–albedo feedback on exoplanets

On Earth, the climate is heavily influenced by interactions with solar radiation and feedback processes. One might expect exoplanets around other stars to also experience feedback processes caused by stellar radiation that affect the climate of the world. In modeling the climates of other planets, studies have shown that the ice–albedo feedback is much stronger on terrestrial planets that are orbiting stars (see: stellar classification) that have a high near-ultraviolet radiation.^[22]

References

^ Budyko, M. I. (1969-01-01). "The effect of solar radiation variations on the climate of the Earth". Tellus. 21 (5): 611–619. Bibcode:1969Tell...21..611B. doi:10.3402/tellusa.v21i5.10109. ISSN 0040-2826.
^ Schneider, Stephen H.; Dickinson, Robert E. (1974). "Climate modeling". Reviews of Geophysics. 12 (3): 447–493. Bibcode:1974RvGSP..12..447S. doi:10.1029/RG012i003p00447. ISSN 1944-9208.
^ Deser, C., J.E. Walsh, and M.S. Timlin (2000). "Arctic Sea Ice Variability in the Context of Recent Atmospheric Circulation Trends". J. Climate. 13 (3): 617–633. Bibcode:2000JCli...13..617D. CiteSeerX 10.1.1.384.2863. doi:10.1175/1520-0442(2000)013<0617:ASIVIT>2.0.CO;2.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Treut, H. Le; Hansen, J.; Raynaud, D.; Jouzel, J.; Lorius, C. (September 1990). "The ice-core record: climate sensitivity and future greenhouse warming". Nature. 347 (6289): 139–145. Bibcode:1990Natur.347..139L. doi:10.1038/347139a0. ISSN 1476-4687. S2CID 4331052.
^ Rantanen, Mika; Karpechko, Alexey Yu; Lipponen, Antti; Nordling, Kalle; Hyvärinen, Otto; Ruosteenoja, Kimmo; Vihma, Timo; Laaksonen, Ari (11 August 2022). "The Arctic has warmed nearly four times faster than the globe since 1979". Communications Earth & Environment. 3 (1): 1–10. doi:10.1038/s43247-022-00498-3. ISSN 2662-4435. S2CID 251498876.
^ Dai, Aiguo; Luo, Dehai; Song, Mirong; Liu, Jiping (10 January 2019). "Arctic amplification is caused by sea-ice loss under increasing CO2". Nature Communications. 10. doi:10.1038/s41467-018-07954-9.
^ Singh, Hansi A.; Polvani, Lorenzo M. (10 January 2020). "Low Antarctic continental climate sensitivity due to high ice sheet orography". NPJ Climate and Atmospheric Science. 3. doi:10.1038/s41612-020-00143-w.
^ Auger, Matthis; Morrow, Rosemary; Kestenare, Elodie; Nordling, Kalle; Sallée, Jean-Baptiste; Cowley, Rebecca (21 January 2021). "Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability". Nature Communications. 10. doi:10.1038/s41467-020-20781-1.
^ ^a ^b ^c Pistone, Kristina; Eisenman, Ian; Ramanathan, Veerabhadran (2019). "Radiative Heating of an Ice-Free Arctic Ocean". Geophysical Research Letters. 46 (13): 7474–7480. Bibcode:2019GeoRL..46.7474P. doi:10.1029/2019GL082914. ISSN 1944-8007.
^ Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; et al. (2021). "Technical Summary" (PDF). IPCC AR6 WG1. p. 76.
^ Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; et al. (2021). "Technical Summary" (PDF). IPCC AR6 WG1. p. 76.
^ Docquier, David; Koenigk, Torben (15 July 2021). "Observation-based selection of climate models projects Arctic ice-free summers around 2035". Communications Earth & Environment. 2. doi:10.1038/s43247-021-00214-7.
^ Sigmond, Michael; Fyfe, John C.; Swart, Neil C. (2 April 2018). "Ice-free Arctic projections under the Paris Agreement". Nature Climate Change. 2. doi:10.1038/s41558-018-0124-y.
^ Wunderling, Nico; Willeit, Matteo; Donges, Jonathan F.; Winkelmann, Ricarda (27 October 2020). "Global warming due to loss of large ice masses and Arctic summer sea ice". Nature Communications. 10. doi:10.1038/s41467-020-18934-3.
^ Wunderling, Nico; Willeit, Matteo (2 December 2021). "A Cloudier Picture of Ice-Albedo Feedback in CMIP6 Models". Frontiers in Earth Science. 9. doi:10.3389/feart.2021.769844.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ Armstrong McKay, David; Abrams, Jesse; Winkelmann, Ricarda; Sakschewski, Boris; Loriani, Sina; Fetzer, Ingo; Cornell, Sarah; Rockström, Johan; Staal, Arie; Lenton, Timothy (9 September 2022). "Exceeding 1.5°C global warming could trigger multiple climate tipping points". Science. 377 (6611). doi:10.1126/science.abn7950. ISSN 0036-8075.
^ ^a ^b Armstrong McKay, David (9 September 2022). "Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer". climatetippingpoints.info. Retrieved 2 October 2022.
^ Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; et al. (2021). "Technical Summary" (PDF). IPCC AR6 WG1. p. 76.
^ Wu, Patrick; Johnston, Paul (2000). "Can deglaciation trigger earthquakes in N. America?". Geophysical Research Letters. 27 (9): 1323–1326. Bibcode:2000GeoRL..27.1323W. doi:10.1029/1999GL011070. ISSN 1944-8007.
^ Harland, W. B. (1964-05-01). "Critical evidence for a great infra-Cambrian glaciation". Geologische Rundschau. 54 (1): 45–61. Bibcode:1964GeoRu..54...45H. doi:10.1007/BF01821169. ISSN 1432-1149. S2CID 128676272.
^ "'Snowball Earth' Might Be Slushy". Astrobiology Magazine. 2015-08-03. Retrieved 2019-06-13.
^ Shields, Aomawa L.; Meadows, Victoria S.; Bitz, Cecilia M.; Pierrehumbert, Raymond T.; Joshi, Manoj M.; Robinson, Tyler D. (August 2013). "The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets". Astrobiology. 13 (8): 715–739. arXiv:1305.6926. Bibcode:2013AsBio..13..715S. doi:10.1089/ast.2012.0961. ISSN 1531-1074. PMC 3746291. PMID 23855332.

External links

Turton, Steve (3 June 2021). "Why is the Arctic warming faster than other parts of the world? Scientists explain". WEForum.org. World Economic Forum. Archived from the original on 3 June 2021.

[1] Budyko, M. I. (1969-01-01). "The effect of solar radiation variations on the climate of the Earth". Tellus. 21 (5): 611–619. Bibcode:1969Tell...21..611B. doi:10.3402/tellusa.v21i5.10109. ISSN 0040-2826.

[2] Schneider, Stephen H.; Dickinson, Robert E. (1974). "Climate modeling". Reviews of Geophysics. 12 (3): 447–493. Bibcode:1974RvGSP..12..447S. doi:10.1029/RG012i003p00447. ISSN 1944-9208.

[3] Deser, C., J.E. Walsh, and M.S. Timlin (2000). "Arctic Sea Ice Variability in the Context of Recent Atmospheric Circulation Trends". J. Climate. 13 (3): 617–633. Bibcode:2000JCli...13..617D. CiteSeerX 10.1.1.384.2863. doi:10.1175/1520-0442(2000)013<0617:ASIVIT>2.0.CO;2.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[4] Treut, H. Le; Hansen, J.; Raynaud, D.; Jouzel, J.; Lorius, C. (September 1990). "The ice-core record: climate sensitivity and future greenhouse warming". Nature. 347 (6289): 139–145. Bibcode:1990Natur.347..139L. doi:10.1038/347139a0. ISSN 1476-4687. S2CID 4331052.

[5] Rantanen, Mika; Karpechko, Alexey Yu; Lipponen, Antti; Nordling, Kalle; Hyvärinen, Otto; Ruosteenoja, Kimmo; Vihma, Timo; Laaksonen, Ari (11 August 2022). "The Arctic has warmed nearly four times faster than the globe since 1979". Communications Earth & Environment. 3 (1): 1–10. doi:10.1038/s43247-022-00498-3. ISSN 2662-4435. S2CID 251498876.

[6] Dai, Aiguo; Luo, Dehai; Song, Mirong; Liu, Jiping (10 January 2019). "Arctic amplification is caused by sea-ice loss under increasing CO2". Nature Communications. 10. doi:10.1038/s41467-018-07954-9.

[7] Singh, Hansi A.; Polvani, Lorenzo M. (10 January 2020). "Low Antarctic continental climate sensitivity due to high ice sheet orography". NPJ Climate and Atmospheric Science. 3. doi:10.1038/s41612-020-00143-w.

[8] Auger, Matthis; Morrow, Rosemary; Kestenare, Elodie; Nordling, Kalle; Sallée, Jean-Baptiste; Cowley, Rebecca (21 January 2021). "Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability". Nature Communications. 10. doi:10.1038/s41467-020-20781-1.

[Pistone2019-9] Pistone, Kristina; Eisenman, Ian; Ramanathan, Veerabhadran (2019). "Radiative Heating of an Ice-Free Arctic Ocean". Geophysical Research Letters. 46 (13): 7474–7480. Bibcode:2019GeoRL..46.7474P. doi:10.1029/2019GL082914. ISSN 1944-8007.

[10] Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; et al. (2021). "Technical Summary" (PDF). IPCC AR6 WG1. p. 76.

[11] Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; et al. (2021). "Technical Summary" (PDF). IPCC AR6 WG1. p. 76.

[12] Docquier, David; Koenigk, Torben (15 July 2021). "Observation-based selection of climate models projects Arctic ice-free summers around 2035". Communications Earth & Environment. 2. doi:10.1038/s43247-021-00214-7.

[13] Sigmond, Michael; Fyfe, John C.; Swart, Neil C. (2 April 2018). "Ice-free Arctic projections under the Paris Agreement". Nature Climate Change. 2. doi:10.1038/s41558-018-0124-y.

[14] Wunderling, Nico; Willeit, Matteo; Donges, Jonathan F.; Winkelmann, Ricarda (27 October 2020). "Global warming due to loss of large ice masses and Arctic summer sea ice". Nature Communications. 10. doi:10.1038/s41467-020-18934-3.

[15] Wunderling, Nico; Willeit, Matteo (2 December 2021). "A Cloudier Picture of Ice-Albedo Feedback in CMIP6 Models". Frontiers in Earth Science. 9. doi:10.3389/feart.2021.769844.{{cite journal}}: CS1 maint: unflagged free DOI (link)

[McKay2022-16] Armstrong McKay, David; Abrams, Jesse; Winkelmann, Ricarda; Sakschewski, Boris; Loriani, Sina; Fetzer, Ingo; Cornell, Sarah; Rockström, Johan; Staal, Arie; Lenton, Timothy (9 September 2022). "Exceeding 1.5°C global warming could trigger multiple climate tipping points". Science. 377 (6611). doi:10.1126/science.abn7950. ISSN 0036-8075.

[Explainer-17] Armstrong McKay, David (9 September 2022). "Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer". climatetippingpoints.info. Retrieved 2 October 2022.

[18] Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; et al. (2021). "Technical Summary" (PDF). IPCC AR6 WG1. p. 76.

[19] Wu, Patrick; Johnston, Paul (2000). "Can deglaciation trigger earthquakes in N. America?". Geophysical Research Letters. 27 (9): 1323–1326. Bibcode:2000GeoRL..27.1323W. doi:10.1029/1999GL011070. ISSN 1944-8007.

[20] Harland, W. B. (1964-05-01). "Critical evidence for a great infra-Cambrian glaciation". Geologische Rundschau. 54 (1): 45–61. Bibcode:1964GeoRu..54...45H. doi:10.1007/BF01821169. ISSN 1432-1149. S2CID 128676272.

[21] "'Snowball Earth' Might Be Slushy". Astrobiology Magazine. 2015-08-03. Retrieved 2019-06-13.

[22] Shields, Aomawa L.; Meadows, Victoria S.; Bitz, Cecilia M.; Pierrehumbert, Raymond T.; Joshi, Manoj M.; Robinson, Tyler D. (August 2013). "The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets". Astrobiology. 13 (8): 715–739. arXiv:1305.6926. Bibcode:2013AsBio..13..715S. doi:10.1089/ast.2012.0961. ISSN 1531-1074. PMC 3746291. PMID 23855332.

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@@ Line 1: / Line 1: @@
 [[File:Ice albedo feedback.jpg|thumb|Diagram of ice–albedo feedback. Ice reflects more light back into space, whereas land and water absorb more of the sunlight.]]
-'''Ice–albedo feedback''' is a [[positive feedback]] climate process where a change in the area of [[ice caps]], [[glaciers]], and [[sea ice]] alters the [[albedo]] and surface temperature of a planet. [[Ice]] is very reflective, therefore some of the solar energy is reflected back to space. Ice–albedo feedback plays an important role in global [[climate change (general concept)|climate change]].<ref>{{Cite journal|last=Budyko|first=M. I.|date=1969-01-01|title=The effect of solar radiation variations on the climate of the Earth|journal=Tellus|volume=21|issue=5|pages=611–619|doi=10.3402/tellusa.v21i5.10109|bibcode=1969Tell...21..611B|issn=0040-2826}}</ref> For instance, at higher latitudes, warmer temperatures melt the ice sheets.<ref>{{Cite journal|last1=Schneider|first1=Stephen H.|last2=Dickinson|first2=Robert E.|date=1974|title=Climate modeling|journal=Reviews of Geophysics|volume=12|issue=3|pages=447–493|doi=10.1029/RG012i003p00447|issn=1944-9208|bibcode=1974RvGSP..12..447S}}</ref> However, if warm temperatures decrease the ice cover and the area is replaced by water or land, the albedo would decrease. This increases the amount of solar energy absorbed, leading to more warming.<ref>{{cite journal|author=Deser, C., J.E. Walsh, and M.S. Timlin|date=2000|title=Arctic Sea Ice Variability in the Context of Recent Atmospheric Circulation Trends|journal=J. Climate|volume=13|issue=3|pages=617–633|citeseerx=10.1.1.384.2863|doi=10.1175/1520-0442(2000)013<0617:ASIVIT>2.0.CO;2|bibcode=2000JCli...13..617D}}</ref> The effect has mostly been discussed in terms of the recent trend of [[Arctic sea ice decline|declining Arctic sea ice]].<ref>{{Cite journal|last1=Pistone|first1=Kristina|last2=Eisenman|first2=Ian|last3=Ramanathan|first3=Veerabhadran|authorlink2=Ian Eisenman|authorlink3=Veerabhadran Ramanathan|date=2019|title=Radiative Heating of an Ice-Free Arctic Ocean|journal=Geophysical Research Letters|language=en|volume=46|issue=13|pages=7474–7480|doi=10.1029/2019GL082914|issn=1944-8007|bibcode=2019GeoRL..46.7474P|url=https://escholarship.org/uc/item/678849wc}}</ref> The change in albedo acts to reinforce the initial alteration in ice area leading to more warming. Warming tends to decrease ice cover and hence decrease the albedo, increasing the amount of solar energy absorbed and leading to more warming. In the geologically recent past, the ice–albedo positive feedback has played a major role in the advances and retreats of the [[Pleistocene]] (~2.6 Ma to ~10 ka ago) ice sheets.<ref>{{Cite journal|last1=Treut|first1=H. Le|last2=Hansen|first2=J.|last3=Raynaud|first3=D.|last4=Jouzel|first4=J.|last5=Lorius|first5=C.|date=September 1990|title=The ice-core record: climate sensitivity and future greenhouse warming|journal=Nature|volume=347|issue=6289|pages=139–145|doi=10.1038/347139a0|issn=1476-4687|bibcode=1990Natur.347..139L|s2cid=4331052}}</ref>  Inversely, cooler temperatures increase ice, which increases albedo, leading to more cooling.
+'''Ice–albedo feedback''' is a [[positive feedback]] climate process where a change in the area of [[ice caps]], [[glaciers]], and [[sea ice]] alters the [[albedo]] and surface temperature of a planet. [[Ice]] is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global [[climate change (general concept)|climate change]].<ref>{{Cite journal|last=Budyko|first=M. I.|date=1969-01-01|title=The effect of solar radiation variations on the climate of the Earth|journal=Tellus|volume=21|issue=5|pages=611–619|doi=10.3402/tellusa.v21i5.10109|bibcode=1969Tell...21..611B|issn=0040-2826}}</ref> For instance, at higher latitudes, warmer temperatures melt the ice sheets.<ref>{{Cite journal|last1=Schneider|first1=Stephen H.|last2=Dickinson|first2=Robert E.|date=1974|title=Climate modeling|journal=Reviews of Geophysics|volume=12|issue=3|pages=447–493|doi=10.1029/RG012i003p00447|issn=1944-9208|bibcode=1974RvGSP..12..447S}}</ref> However, if warm temperatures decrease the ice cover and the area is replaced by water or land, the albedo would decrease. This increases the amount of solar energy absorbed, leading to more warming.<ref>{{cite journal|author=Deser, C., J.E. Walsh, and M.S. Timlin|date=2000|title=Arctic Sea Ice Variability in the Context of Recent Atmospheric Circulation Trends|journal=J. Climate|volume=13|issue=3|pages=617–633|citeseerx=10.1.1.384.2863|doi=10.1175/1520-0442(2000)013<0617:ASIVIT>2.0.CO;2|bibcode=2000JCli...13..617D}}</ref>  The change in albedo acts to reinforce the initial alteration in ice area leading to more warming. Warming tends to decrease ice cover and hence decrease the albedo, increasing the amount of solar energy absorbed and leading to more warming. In the geologically recent past, the ice–albedo positive feedback has played a major role in the advances and retreats of the [[Pleistocene]] (~2.6 Ma to ~10 ka ago) ice sheets.<ref>{{Cite journal|last1=Treut|first1=H. Le|last2=Hansen|first2=J.|last3=Raynaud|first3=D.|last4=Jouzel|first4=J.|last5=Lorius|first5=C.|date=September 1990|title=The ice-core record: climate sensitivity and future greenhouse warming|journal=Nature|volume=347|issue=6289|pages=139–145|doi=10.1038/347139a0|issn=1476-4687|bibcode=1990Natur.347..139L|s2cid=4331052}}</ref>  Inversely, cooler temperatures increase ice, which increases albedo, leading to more cooling.
-== Evidence ==
+== Significance ==
+=== Current ===
-[[File:Greenland Albedo Change.png|thumb|Albedo change in Greenland]]Snow– and ice–albedo feedback tend to amplify regional warming due to anthropogenic climate change. Due to this amplification, the [[cryosphere]] is sometimes called the "natural thermometer" of Earth because changes in each of its components have long lasting effects on the systems (biological, physical and social) of Earth.<ref>{{Cite web|url=https://www.ipcc.ch/report/ar5/wg1/|title=AR5 Climate Change 2013: The Physical Science Basis — IPCC|access-date=2019-06-12}}</ref> Internal feedback processes may also potentially occur. As land ice melts and causes [[eustatic]] [[sea level rise]], it can also potentially induce earthquakes<ref>{{Cite journal|last1=Wu|first1=Patrick|last2=Johnston|first2=Paul|date=2000|title=Can deglaciation trigger earthquakes in N. America?|journal=Geophysical Research Letters|volume=27|issue=9|pages=1323–1326|doi=10.1029/1999GL011070|issn=1944-8007|bibcode=2000GeoRL..27.1323W|doi-access=free}}</ref> as a result of [[post-glacial rebound]], which further disrupts glaciers and ice shelves. If sea-ice retreats in the Arctic, the albedo of the sea will be darker which results in more warming. Similarly, if the Greenland or Antarctic land ice retreats, the darker underlying land is exposed<ref>{{Cite web|url=https://www.ipcc.ch/report/ar5/wg1/|title=AR5 Climate Change 2013: The Physical Science Basis — IPCC|access-date=2019-06-11}}</ref> and more solar radiation is absorbed.
+[[File:Greenland Albedo Change.png|thumb|Albedo change in Greenland]]
+Snow– and ice–albedo feedback have a substantial effect on regional temperatures. In particular, the presence of ice cover makes the [[North Pole]] and the [[South Pole]] colder than they would have been without it. Consequently, recent [[Arctic sea ice decline]] is one of the primary factors behind the Arctic warming nearly four times faster than the global average since 1979 (the year when continous satellite readings of the Arctic sea ice began). <ref>{{Cite journal |last1=Rantanen |first1=Mika |last2=Karpechko |first2=Alexey Yu |last3=Lipponen |first3=Antti |last4=Nordling |first4=Kalle |last5=Hyvärinen |first5=Otto |last6=Ruosteenoja |first6=Kimmo |last7=Vihma |first7=Timo |last8=Laaksonen |first8=Ari |date=11 August 2022 |title=The Arctic has warmed nearly four times faster than the globe since 1979 |url=https://www.nature.com/articles/s43247-022-00498-3 |journal=Communications Earth & Environment |language=en |volume=3 |issue=1 |pages=1–10 |doi=10.1038/s43247-022-00498-3 |s2cid=251498876 |issn=2662-4435}}</ref>, in a phenomenon known as [[Arctic amplification]]. Modelling studies show that strong Arctic amplification only occurs during the months when significant sea ice loss occurs, and that it largely disappears when the simulated ice cover is held fixed. <ref>{{Cite journal |last1=Dai |first1=Aiguo |last2=Luo |first2=Dehai |last3=Song |first3=Mirong |last4=Liu |first4=Jiping |date=10 January 2019 |title=Arctic amplification is caused by sea-ice loss under increasing CO2 |url=https://www.nature.com/articles/s43247-022-00498-3 |journal=Nature Communications |language=en |volume=10 |doi=10.1038/s41467-018-07954-9 }}</ref> Conversely, the high stability of ice cover in Antarctica, where the thickness of the [[East Antarctic ice sheet]] allows it to rise nearly 4 km above the sea level, means that this continent has not experienced any net warming over the past seven decades<ref>{{Cite journal |last1=Singh |first1=Hansi A. |last2=Polvani |first2=Lorenzo M. |date=10 January 2020 |title=Low Antarctic continental climate sensitivity due to high ice sheet orography |url=https://www.nature.com/articles/s41612-020-00143-w |journal=NPJ Climate and Atmospheric Science |language=en |volume=3 |doi=10.1038/s41612-020-00143-w }}</ref>: ice loss in the Antarctic and its contribution to [[sea level rise]] is instead driven entirely by the warming of the [[Southern Ocean]], which had absorbed 35–43% of the total heat taken up by all oceans between 1970 and 2017. <ref>{{Cite journal |last1=Auger |first1=Matthis |last2=Morrow |first2=Rosemary |last3=Kestenare |first3=Elodie |last4=Nordling |first4=Kalle |last5=Sallée |first5=Jean-Baptiste |last6=Cowley |first6=Rebecca |date=21 January 2021 |title=Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability |url=https://www.nature.com/articles/s41467-020-20781-1 |journal=Nature Communications |language=en |volume=10 |doi=10.1038/s41467-020-20781-1 }}</ref>
+Ice-albedo feedback also has a smaller, but still notable effect on the global temperatures. Arctic ice decline between 1979 and 2011 is estimated to have been responsible for 0.21 watts per square meter (W/m<sup>2</sup>) of [[radiative forcing]], which is equivalent to a quarter of radiative forcing from [[CO2]]<ref name=Pistone2019>{{Cite journal|last1=Pistone|first1=Kristina|last2=Eisenman|first2=Ian|last3=Ramanathan|first3=Veerabhadran|authorlink2=Ian Eisenman|authorlink3=Veerabhadran Ramanathan|date=2019|title=Radiative Heating of an Ice-Free Arctic Ocean|journal=Geophysical Research Letters|language=en|volume=46|issue=13|pages=7474–7480|doi=10.1029/2019GL082914|issn=1944-8007|bibcode=2019GeoRL..46.7474P|url=https://escholarship.org/uc/item/678849wc}}</ref> increases over the same period. When compared to cumulative increases in [[greenhouse gas]] radiative forcing since the start of the [[Industrial Revolution]], it is equivalent to the estimated 2019 radiative forcing from [[nitrous oxide]] (0.21 W/m<sup>2</sup>), nearly half of 2019 radiative forcing from [[methane]] (0.54 W/m<sup>2</sup>) and 10% of the cumulative CO2 increase (2.16 W/m<sup>2</sup>). <ref>{{Cite book |chapter= Technical Summary |last1=Arias |first1=Paola A. |last2 = Bellouin |first2= Nicolas |last3 = Coppola |first3 = Erika |last4 = Jones |first4 = Richard G. |last5 = Krinner |first5 = Gerhard |display-authors=4 |chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |year= 2021 |title= IPCC AR6 WG1 |pages=76 }}</ref>
+=== Future ===
+The impact of ice-albedo feedback on temperature will intensify in the future as the Arctic sea ice decline is projected to become more pronounced, with a likely near-complete loss of sea ice cover (falling below 1 million km<sup>2</sup>) at the end of the [[Arctic summer]] in September at least once before 2050 under all [[Shared Socioeconomic Pathways|climate change scenarios]]<ref>{{Cite book |chapter= Technical Summary |last1=Arias |first1=Paola A. |last2 = Bellouin |first2= Nicolas |last3 = Coppola |first3 = Erika |last4 = Jones |first4 = Richard G. |last5 = Krinner |first5 = Gerhard |display-authors=4 |chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |year= 2021 |title= IPCC AR6 WG1 |pages=76 }}</ref>, and around 2035 under the scenario of continually accelerating greenhouse gas emissions.<ref>{{Cite journal |last1=Docquier  |first1=David |last2=Koenigk  |first2=Torben |date=15 July 2021 |title=Observation-based selection of climate models projects Arctic ice-free summers around 2035 |url=https://www.nature.com/articles/s43247-021-00214-7 |journal=Communications Earth & Environment |language=en |volume=2 |doi=10.1038/s43247-021-00214-7}}</ref> Since September marks the end of the Arctic summer, it also represents the nadir of sea ice cover in the present climate, with an annual recovery process beginning in the [[Arctic winter]]. Consecutive ice-free Septembers are considered highly unlikely in the near future, but their frequency will increase with greater levels of global warming: a 2018 paper estimated that an ice-free September would occur once in every 40 years under a warming of 1.5 degrees Celsius, but once in every 8 years under 2 degrees and once in every 1.5 years under 3 degrees. <ref>{{Cite journal |last1=Sigmond |first1=Michael |last2=Fyfe  |first2=John C. |last3=Swart  |first3=Neil C. |date=2 April 2018 |title=Ice-free Arctic projections under the Paris Agreement |url=https://www.nature.com/articles/s41558-018-0124-y.epdf?sharing_token=s5CzjtDj8gf0ZmN6CCHGztRgN0jAjWel9jnR3ZoTv0PLVuAXOp2dJlBdNTJtKWqWAUYJ9Ns6JXBlxiHaipJXlrKpbiBcmkhRc42ypYk5a3aeceQ5dF5hV39PYKz05y5seLV8NH9jDQsSxYOgWrLL-CjbZkxrUf6gYwBnx-vAhRL3KTUq_7I1sz5MHuQESHzcuFa8mIqycanI0sYAgJoCzHIjO-WCVh51qA0aONgHJ5s%3D&tracking_referrer=interactive.carbonbrief.org |journal=Nature Climate Change |language=en |volume=2 |doi=10.1038/s41558-018-0124-y}}</ref> This means that the loss of Arctic sea ice during September or earlier in the summer would not be irreversible, and in the scenarios where global warming begins to reverse, its annual frequency would begin to go down as well. As such, it is not considered one of the [[tipping points in the climate system]].
+Notably, while the loss of sea ice cover in September would be a historic event with significant implications for Arctic wildlife like [[polar bear]]s, its impact on the ice-albedo feedback is relatively limited, as the total amount of solar energy received by the Arctic in September already very low. On the other hand, even a relatively small reduction in June sea ice extent would have a far greater effect, since June represents the peak of the Arctic summer and the most intense transfer of solar energy<ref name=Pistone2019 />. [[CMIP5]] models estimate that a total loss of Arctic sea ice cover from June to September would increase the global temperatures by 0.19 degrees Celsius, with a range of 0.16–0.21°C, while the regional temperatures would increase by over 1.5 degrees. This estimate includes not just the ice-albedo feedback itself, but also its second-order effects such the impact of such sea ice loss on [[lapse rate]] feedback, the changes in [[water vapor]] concentrations and regional cloud feedbacks.<ref>{{Cite journal |last1=Wunderling |first1=Nico |last2=Willeit |first2=Matteo |last3=Donges |first3=Jonathan F. |last4=Winkelmann |first4=Ricarda |date=27 October 2020 |title=Global warming due to loss of large ice masses and Arctic summer sea ice |url=https://www.nature.com/articles/s41467-020-18934-3 |journal=Nature Communications |language=en |volume=10 |doi=10.1038/s41467-020-18934-3 }}</ref> Since these calculations are are already part of every CMIP5 and CMIP6 model<ref>{{Cite journal |last1=Wunderling |first1=Nico |last2=Willeit |first2=Matteo |date=2 December 2021 |title=A Cloudier Picture of Ice-Albedo Feedback in CMIP6 Models |url=https://www.frontiersin.org/articles/10.3389/feart.2021.769844/full |journal=Frontiers in Earth Science |language=en |volume=9 |doi=10.3389/feart.2021.769844 }}</ref>, they are also included in their warming projections under every climate change pathway, and do not represent a source of "additional" warming on top of their existing projections.
+Very high levels of global warming could prevent Arctic sea ice from reforming during the Arctic winter. Unlike an ice-free summer, this ice-free Arctic winter may represent an irreversible tipping point. It is most likely to occur at around 6.3 degrees Celsius, though it could potentially occur as early as 4.5°C or as late as 8.7°C.<ref name="McKay2022">{{Cite journal |last1=Armstrong McKay |first1=David|last2=Abrams |first2=Jesse |last3=Winkelmann |first3=Ricarda  |last4=Sakschewski |first4=Boris  |last5=Loriani |first5=Sina  |last6=Fetzer |first6=Ingo|last7=Cornell|first7=Sarah |last8=Rockström |first8=Johan |last9=Staal  |first9=Arie |last10=Lenton |first10=Timothy  |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=Science |language=en |volume=377 |issue=6611 |doi=10.1126/science.abn7950 |issn=0036-8075}}</ref> <ref name="Explainer">{{Cite web |last=Armstrong McKay |first=David |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer |url=https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/ |access-date=2 October 2022 |website=climatetippingpoints.info |language=en}}</ref>  While the Arctic sea ice would be gone for an entire year, it would only have an impact on the ice-albedo feedback during the months where sunlight is received by the Arctic - i.e. from March to September. This is estimated to have the impact equivalent to a trillion tons of CO2 emissions<ref name=Pistone2019 /> - around 40% of the 2.39 trillion tons of cumulative emissions between 1850 and 2019<ref>{{Cite book |chapter= Technical Summary |last1=Arias |first1=Paola A. |last2 = Bellouin |first2= Nicolas |last3 = Coppola |first3 = Erika |last4 = Jones |first4 = Richard G. |last5 = Krinner |first5 = Gerhard |display-authors=4 |chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |year= 2021 |title= IPCC AR6 WG1 |pages=76 }}</ref>, and would have a global warming impact of 0.6 degrees, with a regional warming between 0.6 and 1.2 degrees.<ref name="Explainer" />
+As land ice melts and causes [[eustatic]] [[sea level rise]], it can also potentially induce earthquakes<ref>{{Cite journal|last1=Wu|first1=Patrick|last2=Johnston|first2=Paul|date=2000|title=Can deglaciation trigger earthquakes in N. America?|journal=Geophysical Research Letters|volume=27|issue=9|pages=1323–1326|doi=10.1029/1999GL011070|issn=1944-8007|bibcode=2000GeoRL..27.1323W|doi-access=free}}</ref> as a result of [[post-glacial rebound]], which further disrupts glaciers and ice shelves.
 === Snowball Earth ===