Context: The Arctic Ocean could be ice-free in summer by the 2030s, even if we do a good job of reducing emissions between now and then. That’s the worrying conclusion of a new study in Nature Communications.
Over the past 30 years, the Arctic has warmed at roughly twice the rate as the entire globe, a phenomenon known as Arctic amplification. Most scientists agree that this rapid warming is a signal of human-caused climate change.
This map shows trends in mean surface air temperature over the period 1960 to 2019. Notice that the Arctic is red, indicating that the trend over this 60-year period is for an increase in air temperature of nearly 4° C (7.2° F) across much of the Arctic, which is larger than for other parts of the globe.
Multiyear ice:
The ice which remains at the end of summer is called multiyear sea ice and is considerably thicker than its seasonal counterpart. It acts as barrier to the transfer of both moisture and heat between the ocean and atmosphere. Over the past 40 years this multiyear sea ice has shrunk from around 7 million sq. km to 4 million.
Blue ocean event:
“Blue ocean event” is defined as when the sea ice area drops below 1 million sq. km. This threshold is used mainly because older, thicker ice along parts of Canada and northern Greenland is expected to remain long after the rest of the Arctic Ocean is ice-free. We can’t put an exact date on the last blue ocean event, but one in the near future would likely mean open water at the North Pole for the first time in thousands of years.
Reasons behind Arctic Amplification:
Change in Albedo:
- When bright and reflective ice (with more albedo) melts, it gives way to a darker ocean (lowering albedo); this amplifies the warming trend because the ocean surface absorbs more heat from the Sun than the surface of snow and ice.
Changing Ocean currents:
- Currents are changing because more melting ice is injecting the Arctic Ocean with freshwater. The missing ice also exposes the surface waters to more wind. This mixes up colder freshwater at the surface and warmer saltwater below, raising surface temperatures and further melting ice.
Changing Weather
- Ocean currents drive the powerful polar jet stream, which moves hot and cold air masses around the Northern Hemisphere. This is a product of the temperature differences between the Arctic and the tropics.
- But as the Arctic warms, the jet stream now undulates wildly north and south. This has been injecting the Arctic with warm air.
- The abundance of thunderstorms in tropics creates a near-constant flow of heat away from the tropics towards the Arctic.
Change in nature of Ice Cover
- Quality of ice cover in the Arctic region is changing. New ice is replacing old ice.
- Old ice is more resilient than new ice, which melts faster. New ice contains more salty water and is more subject to melting, whereas old ice has a higher share of water coming from snow precipitations and is a source of freshwater.
Impacts of Arctic Melting:
- Coastal erosion: Over the Arctic Ocean, sea ice absorbs the impacts of waves and limits shoreline wave erosion. As sea ice retreats farther away from surrounding landmasses, late-summer and autumn storms stir up strong waves that crash onto shore.
- Increase in sea level: Increased wave action caused due to sea ice melt can bend the ice shelves increasing the possibility of glacial retreat. Glaciers that have lost their ice fronts tend to flow faster, and because this process introduces a body of ice into the ocean that was not there previously, it raises sea level which further can lead to coastal flooding.
- Global warming: Sea ice loss leads to increased permafrost thaw, which drives the release of carbon dioxide and methane—an even more potent greenhouse gas. The retreat of sea ice exposes greater expanses of darker ocean water, which absorbs more solar radiation than white sea ice, perpetuating the global warming effect.
- Alteration of ocean current: Massive amounts of very cold glacial-melt water entering warmer ocean waters reduces the thermal contrast between cold and warm waters. It further alters the density differences also thereby leading to slowing down of ocean currents.
- Changes in weather systems: accelerating sea ice melt could be linked to the intensification of Central Pacific trade winds, the emergence of El Niño events, and a weakening of the North Pacific Aleutian Low Circulation — a semi-permanent low pressure system that drives post-tropical cyclones and generates strong storms.
- Loss of biodiversity: Arctic melting is disrupting the behavior of marine mammals and ice-obligate species including polar bears, walruses, and bearded and ringed seals. Restructured food webs, changes in prey populations, the arrival of new marine mammal species (including new predators and competitors), and pathogens from more temperate seas will challenge Arctic species.
- Higher human interference: The loss of Arctic Sea ice could open up new regions to shipping, tourism, and oil extraction. More people living, working, and extracting resources in the Arctic will likely require more infrastructure, and may raise the risk of emergencies needing cleanup or rescue.
