4 ms·

Just a reminder: the climate is a dynamic system with many feedback loops, one of the most prominent feedback systems is albedo (amount of light reflected or ab

Just a reminder: the climate is a dynamic system with many feedback loops, one of the most prominent feedback systems is albedo (amount of light reflected or absorbed). Snow/ice cover (on land or sea) reflects sunlight, cooling the Earth. Bare ground or water absorbs sunlight, warming the Earth. Melting of arctic sea ice is a positive feedback loop that will increase warming and can lead to a progression toward a different climate equilibrium (a warmer one) that could be hard to break out of even if CO2 levels come down.

kbutler 9y ago
How much sunlight does the Arctic get? I've seen discussion that the heat lost from the relatively warm ocean water when not covered by ice exceeds the additional heat absorbed by low albedo, suggesting that lack of ice cover is actually a net negative feedback. I have no personal calculations as to the magnitude of either effect, but I am skeptical of positive feedback loops, as they are inherently unstable. Note that we get significant ice loss every summer, followed by rapid gains in ice, which seems to cast doubt on the significance of any positive feedback.
- teraflop 9y ago
  Of course the sea ice normally returns every winter. Even at a modest 50 degrees of latitude, the insolation in summer is 6 times higher than in winter [1], so over short timescales, seasonal effects are so huge that they obscure the effects of any positive or negative feedback loops. That doesn't mean those loops don't exist and can't be significant over larger timescales. [1]: http://www.applet-magic.com/insolation.htm http://www.applet-magic.com/insolation.htm
  - kbutler 9y ago
    Right, so you have high insolation for some number of days. This provides heat at a rate of 300-500 W/m2 at peak, but that peak drops off, so the average insolation over the course of the year is low in polar areas. This is a positive feedback of open water (albedo ~.1 vs ice ~.6) and is limited by the duration of high insolation over open water. The maximum insolation is at the summer solstice (June) when there has been a smaller decline in arctic ice area (10%? http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/ http://nsidc.org/arcticseaicenews/charctic-interactive-sea-i...) By the date of low ice extent in September, the sun is getting pretty low for polar areas (low angle, low duration, low insolation - see the equinox data in your link: http://www.applet-magic.com/insolation.htm http://www.applet-magic.com/insolation.htm) Open water loses heat much more rapidly than ice-covered water, with the rate dependent on temperature, wind speed, etc. One study found open water heat flux was about 250 W/m2 vs 75 for ice pack in March/April (http://onlinelibrary.wiley.com/doi/10.1029/94JC02485/abstract http://onlinelibrary.wiley.com/doi/10.1029/94JC02485/abstrac...). I didn't find references to give averages or graphs over a year. However long the ocean remains open, it radiates excess heat at an increased rate vs ice pack - a negative feedback of open water, limited by the area and duration of open water.

kbutler 9y ago

How much sunlight does the Arctic get? I've seen discussion that the heat lost from the relatively warm ocean water when not covered by ice exceeds the additional heat absorbed by low albedo, suggesting that lack of ice cover is actually a net negative feedback. I have no personal calculations as to the magnitude of either effect, but I am skeptical of positive feedback loops, as they are inherently unstable. Note that we get significant ice loss every summer, followed by rapid gains in ice, which seems to cast doubt on the significance of any positive feedback.

teraflop 9y ago
Of course the sea ice normally returns every winter. Even at a modest 50 degrees of latitude, the insolation in summer is 6 times higher than in winter [1], so over short timescales, seasonal effects are so huge that they obscure the effects of any positive or negative feedback loops. That doesn't mean those loops don't exist and can't be significant over larger timescales. [1]: http://www.applet-magic.com/insolation.htm http://www.applet-magic.com/insolation.htm
- kbutler 9y ago
  Right, so you have high insolation for some number of days. This provides heat at a rate of 300-500 W/m2 at peak, but that peak drops off, so the average insolation over the course of the year is low in polar areas. This is a positive feedback of open water (albedo ~.1 vs ice ~.6) and is limited by the duration of high insolation over open water. The maximum insolation is at the summer solstice (June) when there has been a smaller decline in arctic ice area (10%? http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/ http://nsidc.org/arcticseaicenews/charctic-interactive-sea-i...) By the date of low ice extent in September, the sun is getting pretty low for polar areas (low angle, low duration, low insolation - see the equinox data in your link: http://www.applet-magic.com/insolation.htm http://www.applet-magic.com/insolation.htm) Open water loses heat much more rapidly than ice-covered water, with the rate dependent on temperature, wind speed, etc. One study found open water heat flux was about 250 W/m2 vs 75 for ice pack in March/April (http://onlinelibrary.wiley.com/doi/10.1029/94JC02485/abstract http://onlinelibrary.wiley.com/doi/10.1029/94JC02485/abstrac...). I didn't find references to give averages or graphs over a year. However long the ocean remains open, it radiates excess heat at an increased rate vs ice pack - a negative feedback of open water, limited by the area and duration of open water.