What is the Jet Stream, and how is Climate Change influencing it?

Our collective understanding of the extreme weather consequences of climate change is limited. Hollywood, that influential cultural mirror, provides us with intriguing glimpses of potential effects of a changed ecosystem. Before we explore how climate change affects our weather, we must first ask: what is the jet stream?

In the 2004 film 'The Day After Tomorrow,' the collapse of the Atlantic Ocean currents triggers a massive superstorm that freezes the entire Northern Hemisphere. Later, in the 2017 film 'Geostorm,' tsunamis, tumultuous tornadoes, and mysterious flame geysers emerge—elements not yet found in Earth's geothermal repertoire.

The point is, most people with a basic understanding realize that our weather is changing, but if you were to ask someone on the street how it will impact their community in the next 10 or 50 years — most of us would probably struggle to provide any kind of accurate prediction.

How Climate Change Will Influence Weather Patterns

Climate scientists, due to their expertise, know more than the general public — but even they don’t always agree on how climate change will specifically impact weather patterns in different regions. A controversial study from 2012 challenged previous assumptions about the mechanisms through which climate change affects our weather: rising temperatures will lead to more heatwaves, hotter summers will result in worse droughts, and a warmer atmosphere will hold more moisture, resulting in heavier rainfall and flooding.

Shifting Weather Patterns

While the study's findings may be correct, it also suggested that something else could be happening — the once predictable flow of Earth's weather is changing. Due to shifts in the behavior of the jet stream, particularly in the middle latitudes, weather patterns are becoming 'stuck,' lingering for extended periods and intensifying local impacts, including severe droughts, floods, and extreme heatwaves.

This concept has sparked debate, as the forefront of any research often has both proponents and critics. However, a study published in the journal Nature Scientific Reports supports the idea that climate change is modifying the world’s weather patterns, especially the wind systems responsible for weather anomalies. A 2012 NASA animation, based on weather and climate data from NASA's MERRA dataset, demonstrates a 30-day pattern of the Northern Hemisphere's jet stream. The jet stream’s behavior is clearly shifting.

What is the Jet Stream?

There are four primary jet streams — the polar jet streams and the subtropical jet streams, two of each. The subtropical jet streams are located closer to the equator, while the polar jet streams are found in both the northern and southern hemispheres.

Jet streams are fast-moving air currents high in the atmosphere that flow from west to east, driven by the Earth's rotation. These currents form when warm air masses collide with cold air masses in the atmosphere.

Jet Streams Generate Weather Patterns

Jet streams play a critical role in shaping our weather. Even though the winds in a jet stream flow in a single direction, the temperature contrast between the poles and the equator causes these winds to form wavy, north-south patterns. When the temperature at the poles rises more quickly than at the equator, it disrupts the balance that governs the jet streams.

"Just as a coaxial cable guides electromagnetic waves to our televisions with minimal energy loss," explains Michael Mann, professor of atmospheric science at Penn State, via email, "the atmosphere traps waves in the jet stream in a way that enables them to travel with minimal energy loss."

Fluctuations in the Jet Stream

When the temperature difference between the poles and the equator is large, the jet stream flows more vigorously and the waves become shorter. However, when the poles warm at a faster rate than the equator, as we are seeing now, the atmospheric waves tend to stretch, and the flow weakens.

"These large, north-south meanders are linked to extreme weather and the phenomenon of weather getting 'stuck' in place, resulting in prolonged regional droughts, floods, and heat waves," Mann explains. "We demonstrate that climate change is making the temperature patterns that foster these conditions more frequent."

Signs of Extreme Weather Events

Extreme weather events are easy to find in recent history, with some regions experiencing prolonged impacts. In 2010, a powerful low-pressure system in Pakistan brought unparalleled monsoon rains, resulting in devastating floods. The disaster claimed 2,000 lives and displaced 18 million people, destroying homes, crops, and livelihoods. Similarly, persistent high-pressure systems have led to catastrophic heat waves and droughts, such as the 2003 European heat wave, which caused 35,000 deaths, the 2010 Russian heat wave and wildfires, the 2011 drought in Oklahoma and Texas, and the 2015 California wildfires.

As we gain a clearer understanding of how climate change is shaping life on Earth, Mann and his colleagues are exploring ways this knowledge can guide us moving forward.

"This paper aims to contribute to the ongoing conversation about the significant dangers that climate change presents," says the author. "Additionally, the data could help us forecast when extreme weather events are most likely to take place."