The evidence of climate change

The evidence of climate change

(Image: Sonny Whitelaw)

Dangerous tipping points : Arctic Sea Ice

Summary

  • The Arctic Ocean is a semi-enclosed ocean, surrounded almost entirely by land—Eurasia, North America, Greenland and some smaller islands. The land keeps most of the sea ice penned up, making it less mobile than sea ice that forms around Antarctica.
  • Sea ice grows throughout the autumn and winter and then melts throughout the spring and summer; it has declined 95% in the past 33 years (Videos 1 & 2).
  • The world’s oceans have absorbed around 93% of global warming to date, and are heating up 40% faster on average than the IPCC estimated in 2013.
  • The Arctic is warming 2-3 times faster than the global average (Fig. 1) in good part because the positive albedo effect of ice is rapidly diminishing (Fig. 2).
  • This is changing the Arctic food web, beginning with phytoplankton
  • Changes in sea ice do not affect sea levels, however this is triggering a cascading series of feedback effects including but not limited to:
Video 1: NASA video showing the rapid decline of sea ice 1978 -2016

Video 2: NASA video showing sea ice loss 2018-2019

Fig. 1: The Arctic is warming twice as fast on average as elsewhere. (Image: NASA)
Fig. 1: The Arctic is warming twice as fast on average as elsewhere. (Image: NASA)

Explainers

The Albedo Effect:

Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it much faster than the snow and ice (Fig. 2). Younger thin ice absorbs reflects less sunlight (and hence absorbs more heat) than multi-year thick ice (Video 1), leading to further loss of ice and increased warming, and so on.

Fig. 2:  (Photo: NASA/ Nathan Kurtz)
Fig. 2: (Photo: NASA/ Nathan Kurtz)

Phenological changes

How plants and animals change the way they behave according to temperature (Video 3). See more about ‘phenology’ on this website.

Video 3: Phenology and ‘mismatches’ in nature.

The Great Oceanic Conveyor Belt:

Also known as Thermohaline current and Atlantic Meridional Overturning Current (AMOC) abruptly shut down when Earth warmed quickly at the end of the Last Glacial Maximum 14,500 years ago, leading to equally abrupt cooling over much of Europe (called the Younger Dryas), and an unstable climate that brought wild weather globally for several thousand years. 

Find out more about this current here (links to a page on this website).


A giant blob of warm water

When the albedo effect creates dark water that absorbs more heat, that heat must go somewhere:

“These warming surface waters are likely migrating down into the blob, which robotic temperature probes, moorings, and oceanographic surveys show is steadily warming and growing. With enough heat to melt the Arctic’s ice three to four times over, the blob could devour the ice from below if the barrier of the cold surface layers ever dissipates… Measurements from the eastern Arctic Ocean show the blob, usually found 150 meters below or deeper, has recently moved up to within 80 meters of the surface… The process, called “Atlantification,” is already well underway in the Barents Sea, north of Norway, where fingers of warm Atlantic water have spread north and risen, melting sea ice even in winter months. The invasion shows no sign of stopping…”Voosen, August 2020.

References and further reading