The cold Spring this year is triggering responses turning natural factors upside down and backwards, confusing causes and effects.  For example, this article at Science Daily Snow chaos in Europe caused by melting sea-ice in the Arctic.  The simplistic appeal to “climate change” is typical: “It is the loss of the Arctic sea-ice due to climate warming that has, somewhat paradoxically, been implicated with severe cold and snowy mid-latitude winters.”  In fact, as we shall see below, it is the wavy Polar Vortex causing both cold mid-latitudes from descending Arctic air, and melting ice from intrusions of warmer southern air.  Importantly, global warming theory asserts that adding CO2 causes the troposphere to warm and the stratosphere to cool.  What we are experiencing this Spring is an unstable Polar vortex due to events of Sudden Stratospheric Warming  (SSWs), not cooling.

Seasoned meteorologist Judah Cohen of AER shows the mechanism this way:

My colleagues, at AER and at selected universities, and I have found a robust relationship between two October Eurasian snow indices and the large-scale winter hemispheric circulation pattern known as the North Atlantic or Arctic Oscillation pattern (N/AO).

The N/AO is more highly correlated with or explains the highest variance of winter temperatures in eastern North America, Europe and East Asia than any other single or combination of atmospheric or coupled ocean-atmosphere patterns that we know of. Therefore, if we can predict the winter N/AO (whether it will be negative or positive) that provides the best chance for a successful winter temperature forecast in North America but certainly does not guarantee it.

He goes on to say that precipitation is the key, not air temperatures, and ENSO is a driving force:

As long as I have been a seasonal forecaster, I have always considered El Nino/Southern Oscillation (ENSO) as a better predictor of precipitation than temperature across the Eastern US. I think this is supported by the observational or statistical analysis as well as the skill or accuracy of the climate models.

There have been recent modeling studies that demonstrate that El Nino modulates the strength and position of the Aleutian Low that then favors stratospheric warmings and subsequently a negative winter N/AO that are consistent with our own research on the relationship between snow cover and stratospheric warmings. So the influence of ENSO on winter temperatures in the Mid-Atlantic and the Northeast may be greater than I acknowledge or that is represented in our seasonal forecast model.


As Cohen’s diagram shows, there is an effect from warming, but in the stratosphere. Global warming theory claims CO2 causes warming in the troposphere and cooling in the stratosphere. So whatever is going on, it is not due to CO2.

Cohen’s interview with the Washington Post.

The current situation is described in Cohen’s most recent post at his Arctic Oscillation blog:

The stratospheric PV always disappear in the spring due to the increasing solar radiation in the polar stratosphere. However, during some springs in addition to the radiative warming of the polar stratosphere, there is also dynamic warming of the polar stratosphere due to the absorption of upwelling Wave Activity Flux (WAFz) from the troposphere. This occurred last spring, which did result in a cool May and even some rare snowfall in the Northeastern US. The predicted return of Ural blocking coupled with Northeast Asia/northern North Pacific troughing is conducive to more active WAFz. The latest PV animation (see Figure ii) shows the stratospheric PV filling (weakening) and meandering over the northern Asia in response to the more active WAFz. This could be the beginning of a dynamically assisted Final Warming that could result in a period of cooler temperatures in parts of the mid-latitudes.

Figure ii. Observed and predicted daily geopotential heights (dam; contours) and anomalies (shading) through April 21, 2021. The forecast is from the 00Z 5 April 2021 GFS ensemble.

Background is at post No, CO2 Doesn’t Drive the Polar Vortex 

via Science Matters


April 13, 2021 at 04:13PM