Sea ice cover in the Arctic Ocean hit an annual summer low in September. At 1.82 million square miles, it was 579,000 square miles smaller than the 1981-2010 average, according to the National Oceanic and Atmospheric Administration.
The ice reaches its maximum each March and its minimum each September.
According to the National Snow and Ice Data Center, the amount of ice that survives the summer melt season has shrunk by 13% per decade relative to the 1981–2010 average.
Arctic sea ice decreases are related to the phenomenon known as Arctic amplification, which according to the NOAA is a more intense warming in the Arctic than over the rest of the globe.
Arctic amplification applies to the current scientific understanding of Earth's climate system, and with model projections of global warming caused by greenhouse gas emissions. Multiple factors contribute to Arctic amplification, and sea ice loss is one of them.
The white surface of sea ice reflects up to 80% of incoming sunlight, deflecting additional energy away from the planet. With less ice present, the dark surface of the ocean absorbs significantly more sunlight energy, leading to further warming of the sea surface and overlying atmosphere, which in turn leads to more melting of ice, and the cycle continues.
Scientists are studying the effects of this feedback loop to help them understand and predict how decreases in sea ice and snow cover will affect the global climate system.
Loss of sea ice affects marine mammals such as walruses, polar bears and seals, and it disrupts the food supply of Arctic residents.
Satellite-based measurements, which began in the late 1970s, have annually reported a decline in sea ice.