The evidence of climate change
(Image: Sonny Whitelaw)
Dangerous tipping points : Arctic Sea Ice
- 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:
- Changing how the Great Oceanic Conveyor Belt, the world’s largest ocean current works (this will affect New Zealand)
- Melting permafrost and methane clathrates, which are releasing more of the greenhouse gasses, carbon dioxide and methane into the atmosphere (this will definitely affect New Zealand).
- Changing global weather patterns: the relatively large temperature difference between the temperature at the poles and the tropics is a key part of how global climate and weather systems work. As the poles are warming 2-3 times faster than elsewhere, the temperature difference is declining (already affecting New Zealand).
- Phenological changes in phytoplankton, which is the base of the food chain and loss of habitat for iconic species such as polar bears and godwits (which migrate to New Zealand).
Video 2: NASA video showing sea ice loss 2018-2019
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.
How plants and animals change the way they behave according to temperature (Video 3). See more about ‘phenology’ on this website.
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.
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
- National Snow and Ice Data Centre (NSIDC)
- (undated) Harvey et al; Equator-to-pole temperature differences and the extra-tropicalstorm track responses of the CMIP5 climate models, NCAS-Climate, Department of Meteorology, University of Reading, UK
- 2020: Guarono et al; Sea-ice-free Arctic during the Last Interglacial supports fast future loss, Nature Climate Change 10 pp928-932
- 2020: Ardyna & Arrigo; Phytoplankton dynamics in a changing Arctic Ocean, Nature Climate Change 10 pp892–903
- 2020: Polyakov et al; Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean, Journal of Climate American Meteorological Society 33/18 pp8107–8123.
- 2020: Timmermans et al; Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins, Science Advances 4/8
- 2020: Voosen; Growing underwater heat blob speeds demise of Arctic sea ice, Science 25 August.
- 2020: Skagseth et al; Reduced efficiency of the Barents Sea cooling machine, Nature Climate Change 10, pp661-666
- 2020: Jansen et al; Past perspectives on the present era of abrupt Arctic climate change Nature Climate Change 10, pp714–721
- 2020: Ouyang et al; Sea-ice loss amplifies summertime decadal CO2 increase in the western Arctic Ocean Nature Climate Change 10, 678–684
- 2020: NASA Earth Observatory: Ice Bridge
- 2020: NASA; Mapping Snow on Arctic Ice
- 2020: Thomas et al; Tipping elements and amplified polar warming during the Last Interglacial, Quaternary Science Reviews 233 / 106222
- 2020: England et al; Tropical climate responses to projected Arctic and Antarctic sea-ice loss Nature Geoscience 13, 275–281
- 2019: Lade et al; Human impacts on planetary boundaries amplified by Earth system interactions, Nature Sustainability 3, pp 119–128
- 2019 IPCC: Special Report on the Ocean and Cryosphere in a Changing Climate
- 2019: NASA: 2019 Arctic Sea Ice Minimum Tied for Second Lowest On Record
- 2019: NOAA Richter-Menge et al; Arctic Report Card 2019
- 2019: National Geographic: The Arctic Is Heating Up September 2019 special issue
- 2019: Thackeray et al. An emergent constraint on future Arctic sea-ice albedo feedback, Nature Climate Change 9, pp972-978
- 2019: Cheng et al; How fast are the oceans warming? Science 363/6423 pp128-129
- 2018 NOAA Arctic Report Card: Executive summary
- 2018 IPCC: Summary for Policymakers of IPCC Special Report on Global Warming of 1.5°C approved by governments
- 2018: Carbon Brief Analysis; Why the IPCC 1.5C report expanded the carbon budget
- 2017: Jones; How the World Passed a Carbon Threshold and Why It Matters, Yale Environment 360 – Yale School of Forestry & Environmental Studies
- 2017: Kashiwase et al; Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone, Nature – Scientific Reports 7, 8170