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Earth's Systems / Water cycle / Snow, ice and meltwater storage / Sea ice and the ice-albedo feedback

Sea ice and the ice-albedo feedback

How sea ice forms, grows, insulates and reflects, how its summer melt exposes dark water that absorbs more sunlight (ice-albedo feedback), and how fast the Arctic and Antarctic covers are changing.

Boundary: where this process starts

Starts with: Seawater cooled to its freezing point forms frazil crystals that bond into sheets; ice then thickens as the ocean loses heat through it to the air

Boundary: where it ends

Ends after: September Arctic sea ice is shrinking about 12-13% per decade, and 3 m2 of September ice is lost per tonne of CO2 emitted; Antarctic sea ice is mostly seasonal: about 18.5 million km2 in winter shrinks to about 2.5 million km2 at summer's end

PARTICIPANTSRESOURCESSea iceOceanAtmosphereArcticSouthern OceanHeatIceSunlightSeawaterSaltImpact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.4Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.70%Impact +3 of 5. Click for details and evidence.30%Impact +4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.↻ reinforces · strong · 0.3Impact +4 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Seawater cooled to its freezing point forms frazil crystals that bond into sheets; ice then thickens as the ocean loses heat through it to the air: makes HeatmakesSeawater cooled to its freezing point forms frazil crystals that bond into sheets; ice then thickens as the ocean loses heat through it to the air: uses up Seawateruses upGrowing ice rejects brine; the dense salty water sinks and helps form the bottom and deep waters that drive the overturning circulation: uses SeawaterGrowing ice rejects brine; the dense salty water sinks and helps form the bottom and deep waters that drive the overturning circulation: makes SaltmakesIce growth slows as ice thickens, because heat must conduct through it; thin ice grows fastest, which damps thinning: uses HeatSea ice insulates the ocean and reflects 50-70% of sunlight (up to 90% with snow cover), while open ocean reflects only 6%: uses HeatSea ice insulates the ocean and reflects 50-70% of sunlight (up to 90% with snow cover), while open ocean reflects only 6%: uses SunlightFate of Arctic winter ice: of about 15.5 million km2 in late winter, roughly 30% survives to September and 70% melts (shares are estimates from the extents): uses IceIce melts: melt ponds (albedo 0.4-0.5) and open water absorb far more sunlight: makes HeatmakesIce melts: melt ponds (albedo 0.4-0.5) and open water absorb far more sunlight: uses up Sunlightuses upIce survives as multiyear ice, which has flushed its brine and is thicker and stiffer than first-year ice: uses IceArctic planetary albedo fell from 0.52 to 0.48 in 1979-2011, adding 6.4 W/m2 of solar input over the Arctic Ocean; globally that forcing is a quarter of the CO2: uses HeatArctic planetary albedo fell from 0.52 to 0.48 in 1979-2011, adding 6.4 W/m2 of solar input over the Arctic Ocean; globally that forcing is a quarter of the CO2: uses SunlightSeptember Arctic sea ice is shrinking about 12-13% per decade, and 3 m2 of September ice is lost per tonne of CO2 emitted: uses IceAntarctic sea ice is mostly seasonal: about 18.5 million km2 in winter shrinks to about 2.5 million km2 at summer's end: uses IcemakesHeat: makesuses upSeawater: uses upusesSeawater: usesmakesSalt: makesusesHeat: usesusesHeat: usesusesSunlight: usesusesIce: usesmakesHeat: makesuses upSunlight: uses upusesIce: usesusesHeat: usesusesSunlight: usesusesIce: usesusesIce: usesStart: Sea ice and theice-albedo feedbackSTARTStart: Sea ice and the ice-albedo feedbackEnd: Sea ice and theice-albedo feedbackENDEnd: Sea ice and the ice-albedo feedbackSeawater cooled to itsfreezing point formsfrazil crystals th…📄1Seawater cooled to its freezing point forms frazil crystals that bond into sheets; ice then thickens as the ocean loses heat through it to the airGrowing ice rejectsbrine; the dense saltywater sinks and hel…📄2 ↗2Growing ice rejects brine; the dense salty water sinks and helps form the bottom and deep waters that drive the overturning circulationIce growth slows as icethickens, because heatmust conduct throu…📄2Ice growth slows as ice thickens, because heat must conduct through it; thin ice grows fastest, which damps thinningSea ice insulates theocean and reflects50-70% of sunlight (…📄2Sea ice insulates the ocean and reflects 50-70% of sunlight (up to 90% with snow cover), while open ocean reflects only 6%Fate of Arctic winterice: of about 15.5million km2 in la…📄1Fate of Arctic winter ice: of about 15.5 million km2 in late winter, roughly 30% survives to September and 70% melts (shares are estimates from the extents)Ice melts: melt ponds(albedo 0.4-0.5) andopen water absorb f…📄1Ice melts: melt ponds (albedo 0.4-0.5) and open water absorb far more sunlightIce survives asmultiyear ice, whichhas flushed its bri…📄1Ice survives as multiyear ice, which has flushed its brine and is thicker and stiffer than first-year iceArctic planetary albedofell from 0.52 to 0.48in 1979-2011, addi…📄1Arctic planetary albedo fell from 0.52 to 0.48 in 1979-2011, adding 6.4 W/m2 of solar input over the Arctic Ocean; globally that forcing is a quarter of the CO2September Arctic seaice is shrinking about12-13% per decade, a…📄3 ↗1September Arctic sea ice is shrinking about 12-13% per decade, and 3 m2 of September ice is lost per tonne of CO2 emittedAntarctic sea ice ismostly seasonal: about18.5 million km2 …📄1Antarctic sea ice is mostly seasonal: about 18.5 million km2 in winter shrinks to about 2.5 million km2 at summer's end
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Seawater cooled to its freezing point forms frazil crystals that bond into sheets; ice then thickens as the ocean loses heat through it to the air
Sea iceOceanAtmosphereSeawaterHeat
Evidence (1) · added by Briangold-Claude
Growing ice rejects brine; the dense salty water sinks and helps form the bottom and deep waters that drive the overturning circulation
Sea iceOceanSouthern OceanSaltSeawater
Evidence (2) · added by Briangold-Claude
  • NSIDC, Science of sea ice, https://nsidc.org/learn/parts-cryosphere/sea-ice/science-sea-ice: Freezing expels salt into brine pockets and the exchange of salt between sea ice and the ocean influences ocean circulation across hundreds of kilometres. (confidence 0.85)
  • Jacobs 2004, Bottom water production and its links with the thermohaline circulation, Antarctic Science 16:427-437, https://doi.org/10.1017/S095410200400224X: Antarctic Bottom Water acquires its characteristics from ventilation by the polar atmosphere and the melting and freezing of ice over the continental shelf, forming the southern sinking limb of the thermohaline circulation. (confidence 0.85)
Ice growth slows as ice thickens, because heat must conduct through it; thin ice grows fastest, which damps thinning
Sea iceHeat
Evidence (2) · added by Briangold-Claude
  • NSIDC, Science of sea ice, https://nsidc.org/learn/parts-cryosphere/sea-ice/science-sea-ice: Ice growth slows as the ice thickens because it takes longer for the heat to pass through the ice. (confidence 0.9)
  • Bitz & Roe 2004, A mechanism for the high rate of sea ice thinning in the Arctic Ocean, J. Climate 17:3623-3632, https://doi.org/10.1175/1520-0442(2004)0172.0.CO;2: Bitz and Roe show that the thickness-growth relationship makes thin ice recover quickly while thick ice thins most under a warming perturbation. (confidence 0.75)
Sea ice insulates the ocean and reflects 50-70% of sunlight (up to 90% with snow cover), while open ocean reflects only 6%
Sea iceSnow and iceOceanSunlightHeat
Evidence (2) · added by Briangold-Claude
⑂ Fate of Arctic winter ice: of about 15.5 million km2 in late winter, roughly 30% survives to September and 70% melts (shares are estimates from the extents)
Sea iceArcticIce
Evidence (1) · added by Briangold-Claude
Ice melts: melt ponds (albedo 0.4-0.5) and open water absorb far more sunlight
Sea iceOpen waterSunlightHeat
Evidence (1) · added by Briangold-Claude
Ice survives as multiyear ice, which has flushed its brine and is thicker and stiffer than first-year ice
Sea iceIce
Evidence (1) · added by Briangold-Claude
Arctic planetary albedo fell from 0.52 to 0.48 in 1979-2011, adding 6.4 W/m2 of solar input over the Arctic Ocean; globally that forcing is a quarter of the CO2
ArcticSea iceOceanSunlightHeat
Evidence (1) · added by Briangold-Claude
  • Pistone, Eisenman & Ramanathan 2014, Observational determination of albedo decrease caused by vanishing Arctic sea ice, PNAS 111:3322-3326, https://doi.org/10.1073/pnas.1318201111: Arctic planetary albedo decreased from 0.52 to 0.48 between 1979 and 2011, an additional 6.4 +/- 0.9 W/m2 over the Arctic Ocean region, equal globally to 25% of the CO2 forcing over that period; cloud changes played a negligible role. (confidence 0.9)
September Arctic sea ice is shrinking about 12-13% per decade, and 3 m2 of September ice is lost per tonne of CO2 emitted
Sea iceArcticHumansIceCarbon dioxide
Evidence (3) · added by Briangold-Claude
Antarctic sea ice is mostly seasonal: about 18.5 million km2 in winter shrinks to about 2.5 million km2 at summer's end
Sea iceSouthern OceanIce
Evidence (1) · added by Briangold-Claude
  • NSIDC, Sea ice overview, https://nsidc.org/learn/parts-cryosphere/sea-ice: Antarctic sea ice covers about 18.5 million km2 in late winter with only about 2.5 million km2 remaining at summer's end; almost all Antarctic sea ice is seasonal. (confidence 0.9)