3 ms·

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

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

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.