Weather is not Climate: And here’s why.

Recent cold snaps and winter storms have taken over the news media with some claiming, “How can global warming be happening when it’s below zero?!” The answer is that the long-term warming trend results in both hot and cold short-term temperature extremes and this article will explain how.



The No Nonsense Science:

Weather is not climate. Weather is the short term changes we see day to day in temperature and precipitation. Climate is defined as the weather averaged over many years.

The polar vortex has always existed and separates, by way of the jet stream, the polar air surrounding the poles to the mild air in the subtropics

As the earth warms, the temperature contrast on either side of the jet stream becomes weaker, and the jet stream becomes wobblier A wobblier jet stream means cold, arctic air will dip into the U.S. more frequently

The warmer air results in increased moisture, and this is increased fuel for these more frequent winter storms

It seems like the media has revolted against the recent cold weather trend with tweets and posts claiming “Wouldn’t be bad to have a little of that good old fashioned Global Warming right now!”. While I won’t begin to unpack the falseness of that statement, I will give you the “good old fashioned” no nonsense science behind it all!

First off, weather is not climate. Climate is the result of every day weather averaged over a long period of time (at least 30 years) in a given region of the world. If it rained one day in your hometown, you wouldn’t argue that you live in a rain-forest, so the analogy also applies to winter weather. My favorite climate scientist and idol, Katherine Hayhoe of Texas Tech put it this way: “I think it is important to say, ‘No, just because it snowed once in winter on the East Coast doesn’t mean that decades worth of observation that’s tracking the warming of the entire planet are somehow invalidated‘”.

It is true that this past month has seen several large winter storms track across the U.S., bringing feet of snow, below freezing temperatures, and cancelling hundreds of flights and closing interstates. This may seem like the nature of winter in January, but is it? With buzz words like “Polar Vortex” being thrown around, it’s time to examine the true meaning of that phrase. The polar vortex does exist, year round in fact, around the arctic circle. It is a pool of extremely cold arctic air that exists at each pole, strengthening for us in the northern hemisphere winter, when the arctic circle is permanently shrouded in darkness, strengthening the temperature contrast with the mid-latitudes to the south. The mid-latitudes stretch from about 30 to 60 degrees north (or south) of the equator, or more simply, about the region of the continental U.S.

When this temperature contrast is strongest in winter, it strengthens the jet stream. The jet stream is a river of fast flowing air in the upper atmosphere (about where planes fly) that can at times have wind speeds exceeding 250 mph from west to east. The jet stream exists as a result of the extreme cold polar air to the north interacting with the milder sub-tropical air to the south, and serves as a barrier between the two. When this barrier dips south, it brings that arctic air into the U.S., and consequently the cold air extremes we are seeing. So what causes this jet stream to dip?

The jet stream does naturally rise and fall, much like an actual river, however we have begun to see this happening more and more frequently with the overall global warming trend. As the earth heats up, it makes the temperature contrast between the polar air and the sub-tropical air less stark. You can think of it as though the ice melted in your iced mocha cold-brew while it sits next to your pumpkin spice latte, and the temperatures become more luke warm as a result. The jet stream then becomes wobblier, and dips and rises more often. In winter, these dips mean more polar air streams across the U.S. creating these extreme cold temperatures and winter storms.

Here you can see the polar vortex and how it affects the jet stream in a warmer world, where it becomes wobblier, allowing cold arctic air to slip south more frequently.

A warmer world also means more moisture available for these winter storms, resulting in more precipitation in the form of snow and freezing rain. Warm air is able to ‘possess’ more moisture than cold air. This is because as air heats up, the particles are more energetic and are more likely to take the form of vapor as you increase the temperature. You can visualize this as the steam that builds up on your bathroom mirror when you’re taking a shower. The warm water coming out of the shower head increases the temperature in the room, which in turn energizes the particles turning many of them into vapor that collects on the mirror. The combination of more moisture and a wobblier jet stream means increased winter storms that also may be more powerful, such as the nor’easters hitting the New England coast.

The next time you hear the news or a friend commenting on the recent cold snap and why this is, you can reference them to the jet stream! There’s no doubt that the polar vortex is naturally occurring and has always been around, however, the influence of climate change has lessened the temperature contrast between air masses and made these extreme cold spells more frequent. The polar vortex is alive and well and always has been, and the influences our changing climate has on it will continue to affect us for winters to come. You may need to get used to these below 0 wind chill temperatures!

