Arctic amplification is the phenomenon where surface air temperatures in higher latitudes are warming faster than in lower latitudes. This phenomenon is commonly described as the Arctic warming faster than the rest of the globe. Arctic amplification is driven by numerous positive and negative feedback loops. The positive feedbacks are described as changes in sea ice and snow albedo, changes in cloud and water vapour, changes in atmospheric circulation and black carbon aerosols.
History
Research and discussions regarding Arctic amplification have started as early as 1968, with climatologist Mikhail Budyko, being one of the first researchers to describe the concept. In his study, Budyko analyzed The Effects of solar radiation and concluded that a reduction in Arctic sea ice does result in increased Arctic temperatures, which are primarily seen through the mechanism of surface albedo feedback. Following this study, in 1974, researchers Manabe and Wetherald demonstrated that climate models can simulate Arctic amplification.
Surface Albedo Feedbacks
Sea ice and snow albedo feedbacks are fast acting feedbacks because they occur seasonally. In a study done in 2010, Miller et al., defined surface albedo as “the reflectivity of that surface to the wavelengths of solar radiation”. It has been documented that sea ice and snow have large albedo’s and thus a change in their extent will strongly influence planetary imbalances. As temperatures warm, the extent of snow and sea ice decreases, leading to higher solar radiation absorption and thus higher global temperatures. Regarding, the speed of these feedbacks, they are fast-acting because they rely on sunlight, and the Arctic primarily has sun during late spring and summer months. A decrease in sea ice and snow extent, means that a greater portion of the surface of the ocean will be exposed to and absorb solar heat. Once fall and winter come, the heat will be released back to the atmosphere, in the form of longwave radiation, leading to arctic amplification.
Vegetation Feedbacks
Vegetation feedbacks occur due to the northwards shift of dark shrub tundra. The replacement of low-growing tundra with dark shrub tundra, leads to the reduction of high-albedo snow. This reduction leads to a higher surface absorption of solar radiation.
Growth and Decay of Continental Ice Sheets
Growth and decay of continental ice sheets is a slow process, because they unfold over millennial timescales. When ice sheets grow and expand, it leads to an increase reflectivity in the Arctic (Earths albedo), which is responsible for the initial cooling amplification. Alternatively, when temperatures rise, continental ice sheets thin out and retreat, exposing more land. This leads to an acceleration in warming, since there is more solar radiation being absorbed.
Cloud Cover and Water Vapour
Cloud cover and water vapour both play a role in arctic amplification, each in a slightly different form. Clouds have two main effects to Arctic temperatures. They act as a cooling effect since they reduce shortwave reflection. However, they also act as a warming effect, since they can increase longwave trapping. During the fall and winter months, many climate models demonstrate that as the Arctic warms, it becomes cloudier leading to clouds hanging lower. This results in enhanced moisture availability and thus greater trapping of outgoing longwave radiation near the surface.
Water vapour concentrations have also been shown to increase as more atmospheric moisture becomes available. Due to water vapour being a greenhouse gas, it additionally leads to greater longwave trapping near the surface and reinforces the concept of arctic amplification.
Black Carbon Aerosols
Black carbon aerosols are a more recent research phenomenon, contributing to arctic amplification. Black carbon is defined as the incomplete combustion of fossil fuels. In contrast to sulfate aerosols, black carbon aerosols are strong solar radiation absorbers and therefore, lead to the warming of the atmosphere. When black carbon enters the Arctic, they can additionally, be deposited on snow and ice, additionally leading to the absorption of solar radiation. The increasing absorption of solar radiation leads to decreases in snow and sea ice extent furthermore intensifying arctic amplification.
Ecosystem Extremes
Ecosystem extremes, marine and terrestrial, due to arctic amplification are occurring. One research paper found that arctic amplification had a strong impact on the composition and productivity of ecosystem. Satellite observations from the study done by Esau et al., found that, from 1982 to 2014, there was a 42% increase in biological vegetation productivity, and only a 1.2% loss in vegetation productivity. Additionally, when they used satellite observations for marine ecosystems, they noticed that the retreat of sea ice has allowed for an influx of Atlantic waters, leading to a more enriched nutrient productivity layer. Furthermore, they noticed that it has also allowed for the northern movement of marine species consequently leading to an increase in fishing vessels.
Coastal Erosion
Coastal erosion in the Arctic, is an important environmental consequence to analyze because it damages infrastructures and threatens the livelihoods of Arctic coastal communities. Coastal erosion is mainly present when there is an increase in global temperatures. However, due to arctic amplification, mean surface air temperature increases faster in Arctic regions, compared to non-Arctic regions. Therefore, the rate of Arctic coastal erosion increases and becomes amplified due to arctic amplification.
Weather Extremes
Extreme weather changes, Arctic and sub-Arctic, are occurring because of arctic amplification, with the most noticeable being increase in extreme weather patterns in mid-latitude zones. However, because amplified signifies intensifying, researchers are predicting that more extreme and intense weather effects (i.e. heat waves) are expected in the near future.
Implications on Mid-Latitude Weather
In recent years, there has been an increase in climate related events in the Arctic. Simultaneously, researchers have observed an increase in climate related events at mid-latitudes. Whether there is a link between these two events, continues to remain unknown, primarily because there have been contradicting results in the literature. For example, most researchers who quantify a linkage between the two phenomena, believe it is due to storm tracks, jet streams, and regional changes in planetary waves.
Storm tracks are the typical paths that cyclones at mid-latitude follow. Arctic amplification increases Arctic temperatures, leading to a weaker temperature gradient and thus changes the frequency, the intensity and the direction of storm tracks.
The polar jet stream is described as fast-flowing ribbon of winds located in the troposphere, that drives weather in the mid-latitudes. It is driven by the difference in temperature between the Arctic and the mid-latitudes. As the temperatures in the Arctic warm, this difference in temperature decreases, leading to a weaker and more curving jet stream.
Planetary waves (Rossby waves) are large-scale meandering undulations and are responsible for the weather in mid-latitudes. The changes in these planetary waves occur when there is a decrease in the difference between Arctic and mid-latitude temperatures. Due to this difference shrinking, larger planetary waves are produced and thereby weaken the stratospheric polar vortex.
In contrast, a study done by Dai and Song, in 2020, demonstrated that impacts due to Arctic amplification are small in mid-latitude regions and further research is needed. Nevertheless, new research is continuously emerging regarding this specific linkage. Therefore, relationships between Arctic amplification and mid-latitude weather should be continuously monitored.