60 degrees North or South
Formation of sea ice:
1. In the high latitudes more heat leaves the system than is inputted creating annual
net deficit in heat budget.
2. Deficit occurs because the sun’s rays hit the surface at a low angle meaning less
energy is spread over a greater surface area, reducing intensity.
3. High ice cover has high albedo so large proportion of incoming solar radiation is
reflected back into space.
4. In Antarctica monthly mean temperatures around coast between -10 and -30
degrees during southern hemisphere winter.
5. Salt content of sea water means it freezes at -2.0 degrees rather than 0. As ice forms
some salt is expelled leaving a colder, more saline seawater.
Global warming and sea-ice
Concern for IPCC is the effects on sea ice; monitored by European Space Agency’s CryoSat-2
which provides year-round accurate data on Arctic sea ice.
Changing albedo in the Arctic is positive feedback.
NOAA Arctic Report 2017:
• Sea-ice minimum was 4.17millionkm2
compared to long term average of 15million
km2
.
• Sea ice thickness reduced from 5m to 1.25m since Cold War.
• Average surface air temperature 2nd warmest since 1900 and Chukchi sea 4 degrees
warmer than average; delay in autumn freeze-up (positive feedback).
• Tundra record permafrost melting and greenness
