Arctic sea ice minimum 2019 – how did it fare this year?

#Neige & Glace, #Changements climatiques, #Arctique, #EUMETSAT

Publié le 9 octobre 2019

The Arctic sea ice minimum is an annual occurrence that usually takes place in the month of September, when the area/volume of Arctic ice has reached its smallest after the “summer melt season”. Sea ice in the Arctic Ocean has been melting faster in recent years due to a rise in global temperatures, which has implications for the rest of the planet and is a driver of climate change.

Kenneth Holmlund, Chief Scientist at EUMETSAT: "The dramatic reduction in Arctic sea ice has far bearing implications. Not only does it change the global weather and climate, it directly affects the local life and livelihood of the indigenous people, whilst also opening up the Arctic for increased commercial exploitation, especially fishing, marine transport, tourism and oil drilling.

"It is therefore important not only to monitor the climate changes, but also to deploy adequate observation systems to ensure safe operations and sufficient support in case of emergencies."

What have we witnessed this year?

Dr Rasmus Tonboe, Sea Ice Researcher at the Danish Meteorological Institute (DMI): "Compared to the last 40 years, for which we have satellite observations of Arctic sea ice, the minimum sea ice extent did not set a new record this year. While being about 2 million km2 below the 1981-2000 average, it is still above the 2012 minimum record. The annual minimum is the second lowest minimum in the 40-year data recorded by satellites since 1979 tied with 2007 and 2016. However, during April and later during July until mid-August 2019, the sea ice extent was record low for the season.

"September 18 marked the end of the melt season and the beginning of the ice growth season. Over the next six months, the sea ice will expand by approximately 10 million km2. The Sun over the North Pole set on September 20 for the autumn equinox and will not rise before March 2020, so temperatures are well below freezing now.

"The melt in the North Pole area started about a week earlier than normal in June and in some regions along the ice edge, the sea ice broke up about a month earlier than what is considered normal. Warm air outbreaks caused sudden melting, for example in North-West Greenland."

The timing of the melt onset is important for the sea-ice energy balance and the sea ice extent. Solar radiation is at a maximum in the Arctic Ocean before mid-summer because of the midnight Sun, the solar angle and because it is less cloudy at this time of the year compared to later during the melt season. 
Photo: Steffen M. Olsen/DMI

The top of the atmosphere above the North Pole receives more solar radiation during midsummer than any other place on Earth. When the snow on the sea ice starts melting, it changes its ability to reflect sunlight. Melting sea ice absorbs more sunlight than cold and freezing sea ice. Therefore, the combination of high temperatures and clear skies in June, when the central Arctic starts melting, can change the sea-ice energy balance so much that an early melt in June is correlated with a low sea ice extent in September.The sea ice cover, or rather the absence of sea ice, has a direct influence on the heating of surface waters during summer. Along the Siberian coast, Baffin Bay, in the Bering Strait and in the Greenland Sea there are currently large areas where the surface water temperature is 2 °C, 3 °C, and even 4 °C above normal levels. The high water temperatures will delay the re-freeze this autumn.

Our eyes in the sky

Amongst many other things, satellites monitor sea ice area and volume. The data derived from their observations (for example, sea ice minimum data) helps scientists gauge the current state of the Arctic. Any abnormalities can be compared to previous years in order to study changes, predict future patterns and determine what is ‘normal’/what might be cause for alarm.

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