It may not be this year, but it may be. These extreme cold outbreaks caused by climate change were generally not supposed to happen according to the models, but the models are understated. Almost all climate change effects are happening generations to a century ahead of projections.
This review looks at Hanna 2024, published December 10, 2024 in Environmental Research – Climate.
Extreme winter cold outbreaks are becoming more common, not less common on a warmer planet. Why? It’s simple climate science, right? The arctic is warming four times faster than the rest of the world. Ice up is coming later, allowing more warmth from land and ocean to be radiated to the atmosphere. This has created literally, four times more energy in the Arctic than there used to be. So, how does this increased polar energy make extreme winter weather down south?
The polar vortex is a very strong maelstrom of winds at both poles that Earth’s rotation spins like a top. Its held in place by the jet stream that zooms around the planet carrying cold fronts from west to east and north to south.
This massive amount of new extra energy in the Arctic has to go somewhere but it is normally held in place by the jet stream and here is how excursions of the polar vortex occur: The jet stream has these giant loops in it that push cold fronts around the planet and the increase in energy makes the loops surge further south than in our old climate, carrying frigid polar air with it. The increased polar energy also makes the jet stream loops move more slowly from West to east, creating stalls in weather systems.
Even though polar regions are warming four times faster than the rest of the world, it’s still bitterly cold in the north and this (warmer) bitterly cold air is still bitterly cold.
These weather system stalls, or the slowing progression of the jet stream, also creates more precipitation in individual storms (Hurricane Harvey and the Halloween floods of 2013 and 2015), or longer lasting dry periods and therefor drier droughts (ongoing).
Now, here is the troubling part of these polar vortex excursions: They are getting worse and they will continue to (likely) get worse but at a faster and faster rate and here’s why: The polar vortex episodes are all about the increased energy in the Arctic and this energy is related to the difference between Arctic warming versus average global warming.
In 2004, the Arctic was warming twice as fast as the global average. In 2009, the Arctic was warming two to three times as fast. In 2021 it was four times as fast, and some places at the poles like the Svlabard Archipeligo it is warming six times as fast. Because the extremeness of polar vortex excursions is related to the extremeness of the difference between global average temperature and polar temperatures, the chances that we will see an event more extreme than what Texas experienced in the 2021 polar vortex excursion event is increasing.
But you might say, isn’t this what happens with cold air outbreaks in our old climate? Yes it is, but there is a difference with all this extra energy from a faster warming arctic. Cold we are experiencing with this early January outbreak is little different than in our normal climate, so far. But these normally cold outbreaks are diminishing in frequency as we warm, making them less likely in our currently warmed climate. It is a little too early to say if this winter outbreak is “colder” than the new normal, but a weakening of the polar vortex has been observed and there is certainly a big winter storm ongoing across much of the US as of this writing.
Another thing said about the 2021 event was that it didn’t break any low temperature records, which is true. But it did break the below freezing hours duration record by a whopping 50 percent revealing that it doesn’t have to be record cold to be unprecedented.
Hanna 2024 has one very important message embedded in an extremely complex climate problem that Google Notebook LM (an AI review tool) created below. In this review, I have simplified (or ignored) all the acronyms and complicated science on artic amplification (polar regions warming faster than the global average), surface-ice albedo feedback (polar warming caused by loss of ice), ice-ocean heat flux feedback (warm water/ice transferring heat to the atmosphere more than no ice/colder ice), Planck feedback (greater heat energy lost to space on a warmer planet), lapse-rate feedback (greater heat loss at higher latitudes because of greater surface warming), latent energy feedback (where less freezing releases less heat energy), and the moisture feedback (where atmospheric moisture –humidity– is the largest greenhouse gas and warming potential in drier areas is greater with proportional changes in moisture content).
Now that you have had a crash course in climate modeling, the thing to remember is not the details of the Planck feedback or ice-ocean heat flux, but that most of these pieces of science are positive feedbacks. That is, they increase energy, and are the technical reasons why polar regions are warming so much faster than the rest of the planet. When combined together (and some of these – singularly on their own) the increase in energy is nonlinear. Think of this nonlinear relationship as the difference in acceleration between gasoline engines and electric vehicle motors where gasoline engines are our old climate and electric vehicles are our new climate. A gasoline powered Ford Mustang can accelerate from zero to 60 mph in 4.5 seconds, but an electric Mustang can reach 60 mph in 3.5 seconds.
Cover image – the view seen out of the author’s kitchen window during Winter Storm Uri, the polar vortex excursion of 2021 in the Northern Hemisphere. Twenty million Texas experienced winter indoors with this event that shut down the Texas grid for an average of four days during extreme cold conditions at times in the single digits. For more on Winter Storm Uri, see this epic article and podcast:
The Texice Disaster, Valentine’s Week, 2021 – Stories of climate change survival, our current emergency, and new solutions to this existential crisis, February 10, 2022
Podcast on Rag Radio, February 10, 2o22
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Here is what Notebook LM says about Hanna 2024, Influence of high-latitude blocking and the northern stratospheric polar vortex on cold-air outbreaks under Arctic amplification of global warming, Environmental Research – Climate, December 10, 2024.
1. Introduction
This document reviews the complex interplay between Arctic amplification (AA), high-latitude atmospheric blocking, and the stratospheric polar vortex (SPV) in influencing cold-air outbreaks (CAOs) in the mid-latitudes. The central question is whether the observed increase in severe winter weather, including disruptive cold spells, is coincidental with or physically linked to AA, and whether increased understanding of these relationships can better prepare society for future extremes.
Key Point: Despite the widely accepted idea that AA will moderate CAOs, recent research suggests AA may contribute to more frequent severe winter weather.
Quote: “It is widely accepted that Arctic amplification (AA)—enhanced Arctic warming relative to global warming—will increasingly moderate cold-air outbreaks (CAOs) to the midlatitudes. Yet, some recent studies also argue that AA over the last three decades to the rest of the present century may contribute to more frequent severe winter weather including disruptive cold spells.”
2. Arctic Amplification (AA)
Rapid Warming: The Arctic is warming approximately four times faster than the global average, particularly since 1980. *Quote: “Over the period 1980–2023 observed annual mean surface air temperatures in the Arctic have warmed about four times faster than the global mean; faster than predicted by climate models.”
Key Feedbacks: AA is driven by a combination of factors:
Surface-ice albedo feedback
Ice-ocean heat flux feedback
Planck feedback
Lapse-rate feedback *Changes in moisture transport and a local greenhouse effect also contribute.
Increased latent energy transport
Moistening Arctic: AA leads to a moistening of the central Arctic due to increased evaporation from newly ice-free ocean areas and advection of moist air, sometimes intensified by Ural blocking (UB) combined with the positive North Atlantic Oscillation (NAO).
Key Point: AA is a complex phenomenon driven by multiple interacting feedback mechanisms and atmospheric dynamics that impact mid-latitudes in complex ways.
3. Cold-Air Outbreaks (CAOs)
Recent Severe Events: Despite AA, recent years have witnessed a number of historic and severe CAOs in the US and Eurasia, which is seemingly at odds with anticipated warming. *Quote: “Despite this Arctic amplification (AA), a surprising number of historic cold-air outbreaks (CAOs) have occurred in the United States (US) and Eurasia in recent years, the frequency of which may even be increasing regionally during the period of AA”
Socioeconomic Impacts: CAOs result in significant economic losses, travel disruptions, energy issues, and fatalities. *Quote: “Severe CAOs cause socioeconomic impacts including economic losses, travel and energy disruptions, and fatalities”
4. High-Latitude Blocking
Definition: Atmospheric blocking refers to quasi-stationary, persistent modifications of the jet stream flow, typically lasting 1-3 weeks. Quote: “An atmospheric block is a quasi-stationary, persistent modification of the jet-stream flow that occurs at mid and high latitudes that typically lasts for one to a few weeks”
Link to Extremes: Blocking events are associated with persistent weather conditions, often leading to extreme weather such as CAOs. *Quote: “Blocking events are associated with persistent weather conditions in the vicinity of the block that frequently leads to extreme weather events in midlatitudes, including winter CAOs”
Uncertain Causality: The physical causes and climate change responses to blocking aren’t fully understood, but they can act as conduits between AA and mid-latitude jet stream changes. Quote: “The physical causes of blocking, and consequently how blocking responds to and influences climate change, are not well understood”
Regional Blocking: Specific blocking regions (Greenland, North Pacific, Barents/Kara Seas) may serve as crucial linkages between the Arctic and mid-latitudes.
For example, the early December 2022 Greenland blocking event coincided with a weakening SPV and intensifying Ural ridge.
Variable Trends: Trends in blocking frequency and intensity vary depending on the metrics and time periods studied, highlighting the need for a multi-metric approach.
5. Nonlinear Theory of Blocking
Nonlinear Multi-scale Interaction (NMI) Model: This theory views blocking as an Arctic/mid-latitude “weather bridge” involving the interaction of synoptic-scale eddies, blocking dipoles, and background zonal flow.
Meridional Potential Vorticity Gradient (PVy): Blocking lifetime is significantly influenced by PVy, which is the north-south gradient of atmospheric features. Quote: “According to NMI theory, the lifetime of blocking is mainly determined by the meridional background potential vorticity gradient (PVy).”
A weaker PVy results in longer-lasting, more intense blocking, favouring cold extremes.
PVy is influenced not only by Arctic conditions, but also midlatitude conditions. Quote: “The magnitude of PVy does not only depend on the value of PVN over the Arctic, but also on the value of PVS over northern midlatitudes.”
Positive Feedback: A positive feedback exists between Barents-Kara Sea (BKS) warming/sea ice decline and Ural blocking:
BKS warming reduces PVy, maintaining the block and potentially leading to more severe CAOs in Eurasia. Quote: “The PVy theory based on the NMI model reveals a positive feedback between UB and BKS warming or sea-ice decline. The background BKS warming or sea-ice decline can reduce PVy, maintaining UB and increasing its quasi-stationarity, which can result in severe and persistent CAOs over Eurasia and the further intensification (reduction) of BKS warming (sea ice).”
Key Point: Nonlinear internal atmospheric dynamics, the occurrence and location of blocking, and the sub-seasonal duration of events are all important factors in the NMI theory.
6. The Stratospheric Polar Vortex (SPV)
Role: The SPV is a mass of cold, cyclonically rotating air in the stratosphere (15-50 km altitude). Its disruptions are linked to mid-latitude winter weather. *Quote: “When the SPV is in an extreme state, being anomalously weak or strong or shifted over continents, this leads to the modulation of large-scale tropospheric circulation patterns, and thereby winter weather in the midlatitudes.”
Types of Disruption: The review details various types of SPV disruption:
Displacements: The SPV centre shifts away from the North Pole, either towards North America or Eurasia. Can lead to CAOs over North America.
Stretching: The SPV elongates, with asymmetric warming over the North Pacific. These are often forced by amplified tropospheric wavenumber 2 and can result in CAOs in Canada and the US.
Wave reflection off a reflective layer limits polar stratospheric warming.
Splits: The SPV separates into two vortices. Often associated with Sudden Stratospheric Warmings (SSWs).
Sudden Stratospheric Warmings (SSWs):
SSWs are characterized by rapid increases in stratospheric temperature and abrupt decreases in zonal winds. They are linked to negative phase NAO and colder weather in Eurasia.
SSWs can be categorised into multiple types depending on the shape of the vortices: displacement, or split. Different types of SSWs have differing surface impacts. *DD-type SSWs have opposite surface temperature responses before and after the event.
DS-type SSWs have more prominent temperature response in mid-latitudes. *SS-type SSWs tend to result in colder than normal weather in both Eurasia and North America.
The pre-existing tropospheric state, such as Ural blocking, is a precursor to SSWs.
New Metric for SPV Disruption: A novel metric, using 50-10 hPa thickness anomaly fields (rather than 100 hPa height), is proposed to isolate stratospheric changes from tropospheric influences when identifying SPV disruptions. This revealed that a strong, pole-centred SPV has become more common recently, which is opposite to the trend suggested by the traditional 100 hPa height metric, suggesting the traditional approach may be influenced by tropospheric changes. Quote: “We propose and demonstrate a new metric to identify SPV disruptions that isolates stratospheric behaviour rather than conflating anomalies in both the stratosphere and troposphere.”
Precursor Conditions:
High pressure over the Ural region can trigger wave propagation that leads to SPV disruption. *The Aleutian low is also an important link between El Nino Southern Oscillation (ENSO) and the SPV.
Stratosphere-Troposphere Oscillation (STO):
The STO is a newly identified phenomenon, a zonal-asymmetric mode, involving the SPV displacing westwards on the intraseasonal time scale (10-60 days).
The STO is linked to an oscillating phenomena with a deep structure from the troposphere to the stratosphere
The mechanism involves vertical and horizontal Rossby wave propagation. *This phenomenon unifies previous studies into one stratosphere-troposphere coupling framework.
7. Role of the Tropics
Tropical Variability: Modes like the Quasi-Biennial Oscillation (QBO), Madden-Julian Oscillation (MJO), and El Niño Southern Oscillation (ENSO) can influence NH climate through teleconnections. Quote: “The QBO, Madden–Julian Oscillation (MJO) and ENSO are well-known modes of tropical atmosphere and oceanic variability that may have teleconnections with NH climate”
QBO: The QBO influences both tropospheric and stratospheric circulation, with a weaker SPV observed during QBO easterly phase (QBOE) winters.
QBOE conditions can interact with Barents-Kara sea turbulent heat fluxes to create specific atmospheric circulation conditions.
MJO: The MJO can influence large-scale flow in higher latitudes, including the Euro-Atlantic region. Quote: “An active MJO in certain phases influences large-scale flow in higher latitudes, such as the Euro-Atlantic.”
ENSO: La Niña conditions with AA can weaken or shift UB, promoting CAOs over East Asia during early winter.
The weakened PVy during the winter of 2022/23 was amplified by anomalous Arctic warming and tropical Pacific cooling.
Key Point: Tropical modes interact to modulate mid-latitude responses, so they must not be assessed in isolation.
8. Large-Ensemble Climate Model Simulations
Need for Large Ensembles: Large-ensemble simulations are crucial for separating forced responses to AA from internal variability. Quote: “For any individual model in PAMIP and other modelling experiments, the ensemble size (typically between 100 and 500) may not be sufficiently large to fully separate forced response from internal variability”
Model Discrepancies: Significant inter-model differences exist, particularly regarding stratospheric responses to Arctic sea-ice loss.
Responses to sea-ice loss vary among models.
Quantifying Internal Variability: Very large-ensemble simulations can robustly quantify internal atmospheric variability. It is important to have larger ensembles (>=400) to reliably estimate responses to AA and extreme events. Quote: “The uncertainty in the forced response to projected Arctic sea-ice loss arising from internal variability has been extensively studied in recent very large-ensemble climate simulations”
9. Conclusions and Recommendations
Key Linkages: Blocking, SPV disruptions, and tropical modes play crucial roles in connecting AA and mid-latitude CAOs.
Improved Understanding: A comprehensive understanding requires consideration of both large and synoptic drivers, and local factors.
Metric for SPV Disruption: Using stratospheric thickness anomalies allows for better characterisation of SPV disruptions.
PVy: The PVy theory provides a robust perspective for linking large-scale and synoptic events, including AA, ENSO, and SPV disruptions.
It also highlights how Arctic warming can lead to more persistent blocking.
Future Research: Investigate the relative importance of large- and synoptic-scale drivers, and local factors in determining the severity of CAOs.
Further research should focus on how changes in tropospheric precursor patterns impact the stratosphere.
The relative contributions of different tropical drivers should be assessed.
Quote: “Research should investigate the relative importance of both large- and synoptic-scale drivers and local factors (orography, snow/ice cover, clouds, surface energy budget, ABL structure) that determine the local severity of extreme CAOs.”
10. Schematic Overview The document includes a summary figure (Figure 13) that provides a schematic overview of the complex interplay between the Arctic, mid-latitudes and the various drivers of change, such as high-latitude blocking, sea-ice concentration and the SPV.