Minggu, 27 September 2020

Arctic sea ice extent drops to 2nd lowest minimum on record - KXAN.com


According to the National Snow and Ice Data Center (NSIDC), this year’s Arctic sea ice extent was the second lowest minimum on record, extending only 1.44 million square miles (969,000 square miles below the 1981-2010 average). A warming global climate, in addition to regional effects like an early-season heatwave and Arctic temps running 14°F to 18°F warmer than average, are said to be the cause of the decrease in sea ice.

Context: sea ice is simply frozen ocean water (not ice locked on land) that grows in the winter months and melts in the summer months. September typically marks the lowest extent of sea ice. Some ice stays frozen all year, covering about 15% of our oceans.

Average September Arctic sea ice extent showing a decreasing trend over the past 30 years

Quick facts:

  • Arctic sea ice minimum’s have been below the long-term average (1981-2010) for the last 18 years
  • The 14 lowest extents in the satellite era have all occurred in the last 14 years
  • Arctic sea ice extents are declining 12.85% per decade
  • The ice is thinning, with more than 70% of it now seasonal rather than thicker, multi-year ice
  • Only 1% of Arctic sea ice is more than 4 years old (an 18-fold drop since 1985)

Positive feedback loop: from bad to worse

A decline in Arctic sea ice is not limited to just melting ice. The loss kicks off a destructive, self-feeding cycle that results in even more melting. We call this process a ‘positive feedback loop’.

Put simply, warmer temps result in increased melting, less ice and more exposed ocean. Because of the ocean’s darker color and low albedo (or ability to reflect the sun’s energy), it absorbs more heat compared to what a layer of sea ice would have (the color white is highly reflective). This gain in energy not only warms the ocean water but it also causes the oceans to emit more energy back into the atmosphere. Both the release and absorption by the ocean produces even warmer temps. This reinforces the process of melting ice, exposing ocean, etc., allowing the process to keep going.

Illustration of a melting sea ice creating a heat spiral ( or positive feedback loop)

In addition to oceans absorbing more heat, melting Artic ice also exposes and thaws permafrost – a frozen layer of rock, sand, dirt and plant materials typically found in the higher latitudes. Once thawed, microbes begin decomposing the plant material (made of carbon), releasing greenhouse gases that further the warming process. Similar to oceans absorbing more of the sun’s energy, greenhouse gases in the atmosphere absorb energy radiating from Earth’s surface, which also results in a rise in global temperatures.

Other effects

Melting sea ice affects a variety of other things, including shipping channels, ocean currents (which in turn, influences atmospheric patterns), wildlife and people’s way of life (hunting, housing, etc.) For example, those who live in the high northern latitudes will build homes on permafrost. If that permafrost thaws or completely melts, the integrity of those structures are compromised.

DATA: National Snow and Ice Data Center (NSIDC)
GRAPHICS: Climate Central

The Link Lonk

September 28, 2020 at 07:40AM

Arctic sea ice extent drops to 2nd lowest minimum on record - KXAN.com



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