Climate science at a glance
- Changes that occur in one part or region of the climate system can affect others.
- Studies have linked record warm temperatures in the Arctic to changes in atmospheric circulation patterns in the midlatitudes.
- The IPCC fifth assessment report states, “it is likely that circulation features have moved poleward since the 1970s, involving a widening of the tropical belt, [and] a poleward shift of storm tracks and jet streams.”
What is large scale circulation?
Large-scale atmospheric circulation is driven by dynamic processes including wind and pressure systems that determine where it is dry, where it is wet, where it is hot and so on. Changes in large-scale atmospheric circulation are known as "dynamic changes". Dynamic processes are in contrast to thermodynamic processes, which include energy exchanges and phase changes related to land‐atmosphere interactions and convective processes.
Differences between the Northern and Southern Hemispheres
Compared to the Northern Hemisphere, the Southern Hemisphere has a lot more open ocean. Notably, there is a band of water North of Antarctica and below Australia, Africa and South America that is completely uninterrupted by land masses. This open band allows for a strong circumpolar ocean current around Antarctica that is unique to the Southern Hemisphere. The strong circumpolar current creates atmospheric circulation patterns throughout the Southern Hemisphere that are more “zonally symmetric”—a meteorological term that means more consistent across latitudes.
Atmospheric circulation and winds are being displaced toward the poles
In recent decades, global atmospheric circulation structure and associated winds have been displaced toward the poles. Trends associated with these displacements are important signals of climate change. Observed trends include the poleward expansion of the Hadley cell, the poleward shift and increase in mid-latitude westerly winds and contraction of the northern polar vortex.
Changes in the Arctic have global implications
Disruptions to the natural cycles of arctic sea ice, land ice, surface temperature, snow cover, and permafrost affect the amount of warming, sea level change, carbon cycle impacts, and potentially even weather patterns in the lower 48 states. Recent studies have linked record warm temperatures in the Arctic to changes in atmospheric circulation patterns in the midlatitudes.
Large scale global circulation change trends
- There has been a northward shift in winter storm tracks since detailed observations began in the 1950s and an associated poleward shift of the subtropical dry zones.
- Arctic warming is linked to the frequency and intensity of severe winter storms in the United States.
- Depending on the indicator under investigation, scientists have observed tropical widening by 0.3 to 3.1° latitude per decade since 1979, with a consensus widening of about 1.4°. (Note: Part of the wide range is because the boundary between the tropics and extratropics is not well-defined and depends on the definition of specific indicators of tropics width—such as the position of the jet stream, where surface winds change from westerly to easterly or physical indicators like ozone concentration and humidity.)
- Research indicates that extratropical cyclones have shifted toward the poles in both hemispheres over the past 50 years, with further but limited evidence showing a decrease in wind storm frequency at mid-latitudes. Mid-latitude westerly winds have generally increased in both hemispheres.
Studies attribute large scale global circulation change to global warming
- (Mann, Rahmstorf, Kornhuber et al. 2017): This study finds a clear human fingerprint behind the increase in temperature distributions favoring planetary wave stalling.
- (Francis and Skific, 2016): The disproportionate warming in the Arctic warming and resulting weakening of the poleward temperature gradient is causing the Northern Hemisphere circulation to assume a more meridional character (i.e. wavier).