Atmospheric Sciences Research Spotlight

Polar Warming Makes the Jet Stream Stable, Not Wavy or Blocked

An idealized climate model suggests polar warming stabilizes the jet stream and reduces atmospheric blocking at midlatitudes.


Over the past few years the working hypothesis among many climate scientists is that global warming—specifically strong polar warming—is causing an increase in extreme weather events at midlatitudes. The leading proposed mechanism revolves around two main factors: the midlatitude jet stream and atmospheric blocking. Although the idea has been well covered in public discussions and in the media, the actual physical basis behind it is still under considerable debate. In their new study, Hassanzadeh et al. suggest that previous research has overlooked one crucial detail, and in the process gotten the connection between polar warming and midlatitude extreme weather backwards.

Based on previous research, the proposed mechanism tying polar warming to extreme weather worked like this: By increasing the temperature in the Arctic faster than at the equator, climate change is reducing the meridional pressure and temperature gradients, and the speed of west-to-east zonal winds. Slower winds cause a more “wavy” jet stream and more incidences of atmospheric blocking at midlatitudes. Atmospheric blocking causes regions of high or low atmospheric pressure to become stuck in place, causing weather patterns to stagnate for days or even weeks at a time, resulting in heat waves, cold spells, long, deep droughts, or periods of seemingly endless precipitation.

Using a highly idealized model of atmospheric circulation, however, the authors of the current study show that this previous research had overlooked one important factor: polar warming doesn’t just reduce the meridional pressure and temperature gradients; it also reduces the variabilities of pressure and temperature at the jet stream’s altitude. Polar warming, they find, stabilizes the atmospheric circulation.

In their idealized model, which accounts for changes in pressure and temperature variabilities, the authors found that rather than making the jet stream wavier and causing more atmospheric blocking, polar warming is actually streamlining the jet stream and reducing the incidence of blocking events. (Geophysical Research Letters, doi:10.1002/2014GL060764, 2014)

—Colin Schultz, Freelance Writer

Citation: Schultz, C. (2015), Polar warming makes the jet stream stable, not wavy or blocked, Eos, 96, doi:10.1029/2015EO023125. Published on 3 February 2015.

© 2015. The authors. CC BY-NC 3.0
  • STeamPlayer

    This is one of those findings that seems quite intuitive in hindsight. The first piece is the well-documented observation that global warming is disproportionately affecting the polar regions. This is possibly a simple consequence of heat transfer: starting from a pre-Anthropogene steady state, we’ve imposed extra heat on the planet, and one would expect most of that heat to initially flow to the coolest regions. The second piece is that heating the coolest regions decreases the temperature contrast between low and high latitudes, which would tend to reduce the overall energy available to drive planetary weather, hence we should expect in general fewer and less intense extreme events (except for heat waves of course).

    And kudos to eos for continuing to report on quality research papers regardless of whether they fit the scientific consensus. There’s little doubt that anthropogenic warming is occurring, but the evidence for an accompanying increase in extreme weather events (again, other than hot weather) is much thinner, as acknowledged in the most recent IPCC report.

  • Larry Dingman

    It does seem that the jet stream has been very “wavy” lately, causing western US to be unusually warm and the eastern US to be cold. AGUWhat did the original tank experiments show about the relation of Rossby-wave amplitudes and latitudinal temperature gradients?

  • Barb Richman

    Please note that Research Spotlight articles summarize research that has been published in AGU journals and that has been selected by the AGU journal editor to be highlighted. You might want to contact the authors of the journal article directly. — Barbara T. Richman, Editor in Chief, Eos

  • The claim made in this article flies in the face of direct observations. Makes me wonder what the aim is here (?). Looks like more denialist obfuscation designed to confuse the lay person.

    • Pedram Hassanzadeh

      Hi Edward, I am the lead author of this paper and I assure you that the sole purpose of this work is to
      improve our understanding of extreme events and how they might change in the future. Direct observations and climate models have produced very conflicting results regarding how blocking events and waviness of the jet streams change with Arctic warming. You might be interested in looking at a recent article by two of the experts of this field that summarizes the current state of understanding
      of this problem:
      Barnes, E. A. and Screen, J. A. (2015), The impact of Arctic warming on the midlatitude jet-stream: Can it? Has it? Will it?. WIREs Clim Change. doi: 10.1002/wcc.337

      • Pedram,
        Thanks for the reply and the references for me to read. I must confess to some confusion as it appears to me that the arctic jet stream has become less stable in recent years as it appears to be slowing.

        In his report of your work Schultz uses the phrase, ” Using a highly idealized model of atmospheric circulation” you have somehow been able to turn the issue ‘up side down’ if you will. The article make no mention as to what your assessment of whether climate issues are any type of threat and what, if anything, we should be doing about it. I would be keen to get you position on that. I realize that any particular persons position (especially mine) has little bearing on reality. However, if your claim is that your work is “I assure you that the sole purpose of this work is to improve our understanding of extreme events and how they might change in the future.” as stated then what do you consider is mankind’s best course of action to take? Simply hoping to understand how continuing asymmetric polar warming might affect future weather events seems a bit remote from the problem.

        I realize that “models” have returned incoherent results (to the point of differing from already observed events) and that relying on them is possibly foolhardy. As you know, missing even one vector will skew any results. This is why those who deny that a climate problem exists often point to failed models as proof that climate scientists are perpetrating some elaborate hoax just to keep grant money flowing or to protest possible future carbon taxes, etc,,

        Thanks again and I look forward to further discussing this issue with you.
        Best regards,