Monthly sea ice measurements began in the late 1970s. Polar ice has an important role in controlling the planet's temperature due to a process called the albedo effect. Basically, this means that the whiter a surface is the more light and heat it reflects. Sea ice, thus, reflects a great deal of heat back out into space. The more ice, the cooler the temperature, resulting in the formation of more ice. Over long time spans this can lead to an ice age The albedo effect works in the opposite direction as well. If temperatures are warm enough to melt the ice less heat is reflected into space. As melting continues open ocean is exposed. Open ocean being much darker absorbs heat, further raising the temperature, resulting in further melting. Ice levels naturally wax and wane with ice melting in the summer and increasing during the winter. However, large swaths of the Arctic have historically been covered in ice year round, while Antarctic sea ice largely melts in the summer.
The first set of charts show sea ice levels in the Arctic and Antarctic by year. The second set of charts group the same data by month. Notice the steep decline in Arctic sea ice in recent years across all months compared to the 1980s, particularly 2012 and 2016. Antarctic sea ice has actually been growing in recent years. Given the rise in global temperatures it is unclear why this is happening. Several theories have been put forward. One is that the hole in the ozone layer over Antarctica has changed the polar vortex around the continent, shielding it from the greater global climate. Another theory involves. the Interdecadal Pacific Oscillation. It has been in a negative phase which led to cooling in tropical regions of the Pacific, thus leading to the Antarctic's sea ice increase. The Interdecadal Pacific Oscillation has recently flipped into a positive phase, causing warming in the tropical Pacific, which according to the theory, should slow or reverse ice growth. So far this seems to be the case as ice levels were only average in 2015 and fell to record low levels in November and December 2016.
Each colored bar represents one month of ice level anomalies. Monthly anomaly measurements date from 1979. Hover over a bar to see the anomaly levels for that month. Scroll down to track ice levels over time. Anomalies are based on the overall monthly average, 11.84 million square kilometers for the Arctic and 12.04 million square kilometers for the Antarctic. NOAA data average values are not normalized by month. Anomalies are relative to the 1981-2010 averages.