Arctic Amplification and Arctic Oscillation
- The Arctic Oscillation is responsible for cold air outbreaks in the Great Lakes region.
- How the Arctic Oscillation might change in a warming climate remains a subject of active research.
- Cold air outbreaks are likely to contribute to the rapid formation of lake ice with seasonal consequences for lake levels.
- Plausible scenarios for the future include general winter-time warming punctuated with short, intense cold spells.
What is the Arctic Oscillation?
The Arctic Oscillation (AO) is a phenomenon that describes how surface air pressure patterns relate to each other in the mid- to high-latitudes. This relationship influences the jet stream, which is a band of strong winds in the upper atmosphere that generally separates warm and cold air. Consequently, these strong winds influence weather in the midlatitudes, including the Great Lakes.
The AO has two phases – positive and negative. It is typically measured via the AO index, which numerically describes the strength of the AO. During the positive phase of the AO, the jet stream is typically faster and located farther north, keeping cold polar air confined to the Arctic, and resulting in warmer, drier winter weather. During the negative phase, the jet stream is weaker and wavier, leading to colder air being able to extend southward into the Great Lakes region. The AO is naturally quite variable, and can fluctuate daily, monthly, seasonally, or annually. It is difficult to predict the behavior of the AO beyond a few days. 1
What is the Arctic Amplification?
Arctic Amplification (AA) is the name given to the phenomenon of higher latitudes, the polar and Arctic regions, warming faster than lower latitudes, equatorial regions, due to climate change. AA has become one of the clearest signatures of climate change over the last few years due to the magnitude and acceleration of warming that has occurred since 1990. The Arctic has been warming at twice the rate of the global average surface temperature as a result of positive feedback mechanisms, or processes that act to enhance or amplify themselves.
An important part of Arctic Amplification is related to melting ice in the region. Ice is a very good reflector of incoming solar radiation as it has a high surface reflectivity, or albedo. This high albedo results in a low amount of solar radiation being absorbed, and a majority being reflected. However, as temperatures in the Arctic warm, ice begins to melt. The ice is replaced by darker seawater or land, resulting in a lower surface albedo, and more solar radiation being absorbed than reflected. This increase in absorption causes a temperature increase that amplifies warming, leading to even more ice melting, or a positive feedback. Additionally, this melting ice often has bubbles of methane or other greenhouse gases trapped within it. Once the ice melts, these gas bubbles get released into the atmosphere, where they contribute to global and regional temperature rise.
The Potential Relationship Between Arctic Oscillation and Arctic Amplification
Recently, extensive research has been performed to determine whether there is a relationship between AA and the AO, and thus the weather in the Great Lakes region. Specifically, multiple studies have tried to link these two phenomena by examining the frequency of extreme events. However, the impacts of AA on the AO are still uncertain, as definitive signals cannot be distinguished from historical variability at this point in time.
Implications for Long-Term Planning
The Great Lakes region has always been influenced by the Arctic Oscillation, as the negative phase of the Arctic Oscillation is associated with cold air outbreaks. In the future, it is reasonable to expect that similar events will occur, however, there is ambiguity around whether there will be changes to the frequency and intensity of these events. One of the most robust signals we have is warming of the Arctic, and we expect this to continue. Seasonal cooling associated with the dark, polar winters will, however, continue to occur. Hence, cold, polar air will continue to form. However, due to Arctic Amplification, the spatial extent of that air is likely to be smaller, and the seasonal occurrence likely to be more confined to midwinter. 2
With regard to plausible scenarios for planning, scenarios still need to consider cold air outbreaks and the influence that they will have on regional climate as well as on infrastructure and commerce. The cold air outbreaks need to be considered in the context of a background that is, in general, warming. Such a scenario would be a general increase in temperature punctuated with cold air outbreaks. (Much like the 2020-2021 winter.) As the climate continues to warm and our understanding of the regional response in the Arctic improves, the scenarios would need to be modified based on the science-based evidence.
- Francis, Jennifer A, Vavrus, Stephen J, and Cohen, Judah. “Amplified Arctic Warming and Mid‐latitude Weather: New Perspectives on Emerging Connections.” ReviewArticle. Wiley Interdisciplinary Reviews. Climate Change 8, no. 5 (2017): n/a. doi:10.1002/wcc.474.
- King, Martin P, King, Martin P, Hell, Momme, Hell, Momme, Keenlyside, Noel, and Keenlyside, Noel. “Investigation of the Atmospheric Mechanisms Related to the Autumn Sea Ice and Winter Circulation Link in the Northern Hemisphere.” Climate Dynamics 46, no. 3 (2016): 1185–95. doi:10.1007/s00382-015-2639-5.