I predicted several days ago that some people would be tweeting that this early season snowstorm in parts of the Rocky Mountain region somehow refutes anthropogenic climate change. Rob Bailey, a computer engineer in Ohio, brought the Tweet at this link to my attention. I am sure there are many more just like it. It was as predictable as the sunrise or a pendulum changing sides. By now, we are used to seeing people tweet such things on a cold day or when it snows. The counter punch that I often hear is that “people do the same thing with a hot day or a heatwave.” The reality is that cherry-picking one day, one storm, or one week of weather to describe climate change is problematic and may reveal a lack of understanding of weather and climate. Here’s why the snowstorm in the Rockies and surrounding regions says nothing about climate change.
Temperature anomalies in the U.S. showing that most of the country is warmer than normal but colder ... [+]
Before I head too far down this rabbit hole, I want to consult the American Meteorological Society Glossary of Meteorology for basic definitions of “weather” and “climate.” According to the Glossary:
Weather: The state of the atmosphere, mainly with respect to its effects upon life and human activities...As distinguished from climate, weather consists of the short-term (minutes to days) variations in the atmosphere....Climate: The slowly varying aspects of the atmosphere–hydrosphere–land surface system. It is typically characterized in terms of suitable averages of the climate system over periods of a month or more, taking into consideration the variability in time of these averaged quantities.
This definition is your social media antidote for that Tweet that you see dispelling climate change because of this storm or the temperature on a given day.
Ok, I will now turn to this snowstorm. According to the National Weather Service (NWS) in Great Falls, Montana over 2 to 3 feet of snowfall has fallen in the storm. A public information station issued on September 29th by the National Weather Service said that the highest amount was about 40 inches at Browning at the time of writing. According to the NWS, blizzard warnings are still up for many locations.
A couple of points are worth noting. People who make contrarian arguments about climate change often bring up cold events (Remember the snowball in Congress). In reality, there is nothing unusual about snowfall at this time of year in the Mountain West. In 2017, meteorologist Jon Erdman wrote at Weather.com:
Snow can fall over the highest peaks of the Rockies even in late summer. September snow is considered average in the Washington Cascades, the Bitterroots and highest peaks of Colorado. Otherwise, October typically heralds the arrival of the season's first flakes in lower elevations of Montana, Wyoming, eastern Idaho, the Wasatch, Colorado's foothills and mountain valleys, and the mountains of northern New Mexico.
According to a table in Erdman’s article, the earliest snow for Great Falls, Montana was August 22nd, 1992, and the average first snow falls by October 2nd. The bottom line is that there is nothing climatologically-weird about snow there right now.
So why is the region experiencing such record cold and snow conditions in terms of magnitude of the event? To answer this question, we have to look to the jet stream. According to the NWS Glossary, the jet stream is a region of “relatively strong winds concentrated in a narrow stream in the atmosphere, normally referring to horizontal, high-altitude winds....The position and orientation of jet streams vary from day to day.” The wavy pattern of the jet stream is a very strong determinant of general weather patterns, particularly in terms of temperature and wetness. With this storm, the jet stream plunged southward bringing extremely cold air into the region. An upper-level low approaching from the Pacific region supplied the moisture.
To be clear, this is a weather event. I am not attributing it to climate change at all. However, I want to conclude with something that is very counterintuitive to many people. There is a growing body of evidence (and a few counter-narratives) in the peer review literature that suggests that because the Arctic region is warming, there is less of a difference in temperature between the polar and tropical regions. That difference, called a gradient, is what determines the strength of the jet stream. If the difference is smaller due to so-called Arctic Amplification (warming in the Arctic), the jet stream would be wavier. The “so what” is that a jet stream with greater wave amplitude means more extreme troughs or “dips” with cold air and more extreme ridges or “humps” with warm air. In other words, the extremes on both sides of the temperature range are amplified.
Warming and The Jet Stream
In addition to Arctic amplification, there is a credible body of scientific literature that finds that extreme snowfall events may be connected to climate change. The NOAA National Centers For Environmental Information website says:
Years with heavy seasonal snow and extreme snowstorms continue to occur with great frequency as the climate has changed....
The physics behind such relationships may be baffling to many people because the concept of “climate warming” and cold things doesn’t make sense to them. However, I have often found that there are many people who don’t believe that it can be cold in a desert either. The reality is that a warming atmosphere-ocean system can prime rainstorms (and snowstorms) with greater moisture availability. A 2018 paper published in the Bulletin of the American Meteorological Society asked “Was the January 2016 Mid-Atlantic Snowstorm “Jonas” Symptomatic of Climate Change?”
Again, I want to be crystal clear that I am not linking this current blizzard to climate change. However, I am establishing that the knee-jerk reaction of some to use such an event to refute climate change is silly and may even illustrate a lack of understanding of the current body of scientific literature.
