(Photo by Daniel J. Mancuso, Illinois Valley News)
If the climate is warming then why was this past winter so cold?
Firstly, it’s important to distinguish between weather and climate: Weather reflects conditions of the atmosphere over a short period of time; climate is how the atmosphere ‘behaves’ over relatively long periods of time.
Scientists learn about climate, going back tens of thousands of years, as well as individual weather years, by studying coral reefs, frozen glaciers, ice caps, sediments buried at the bottom of the oceans and lakes and tree rings.
Reliable weather records have been kept since about 1850 and 10 of the warmest years in the historical record have all occurred since 2010. Clearly, the climate is warming. So again, why have some locations (including much of the United States) experienced a cooler-than-average winter?
Also, while it seems logical that a warming climate would melt polar ice and dry areas would become even drier – what about all the huge floods, mega-hurricanes, tornado outbreaks and extreme snowstorms happening worldwide?
In the simplest of terms, scientists say much of the chaos is about the changing jet streams. The warming atmosphere is altering the positions of the planet’s four major jet streams that exist high in the atmosphere (5 to 9 miles above Earth’s surface).
One can think of the jet streams as blowing ribbons of wind and gases, that if visible, would look a lot like rivers. Encircling the Earth in fast-moving currents ranging from 120 to 250 miles-per-hour, the jet streams play a critical role in the location and severity of weather events.
For thousands of years, the two polar jet streams gently undulated near the north and south poles, while the two subtropical jet streams circumnavigated the planet near the equators. Small movements in the jet streams have always caused changes in the winds, affecting conditions nearer to Earth’s surface. These movements create areas of high and low air pressure, which shapes weather.
Even minor changes in the “waviness” of either the polar or subtropical jet streams are well known to cause dramatic weather changes in mid-latitude regions – which is why meteorologists are constantly pointing out the locations and behaviors of the jet streams.
But now, especially in the past few decades, ever-increasing dips and troughs in the jet stream have been recorded, prompting scientists to research whether these dramatic changes are being caused by a warming planet.
One renowned scientist, John Wettlaufer, Professor of geophysics, mathematics, and physics at Yale University, along with his team of international colleagues, have concluded that the nearly 40 billion tons of carbon dioxide emitted into the atmosphere by human activities each year is indeed disrupting the jet streams. Their recent study, published in the Proceedings of the National Academy of Sciences journal, offers compelling evidence to back their theory.
“As the planet warms, we predict that the land-ocean contrast of atmospheric heating enhances the meandering in the jet stream and that implies more of these extreme weather events, such as what we have experienced this summer in Kentucky,” Wettlaufer said, referring to that state’s intense precipitation and crippling floods in the summer of 2022.
Getting back to Oregon’s cold winter: The jet streams create barriers between masses of warmer and cooler air, so when the Arctic jet stream meanders dramatically toward the south, it carries pockets of cold air with it. And if the polar jets stream slows or stays in place, then the icy air also hovers and the weather below stays frigid, producing heavier than normal snowfalls (or, where temperatures are warmer, torrential rains).
Meteorologists often refer to this as a polar vortex: which is simply a large area of low pressure and cold air that always surrounds both of the Earth’s poles. The ‘vortex’ refers to the counter-clockwise air flow that tends to keep the colder air closer to the poles. The vortex weakens in summer, but throughout the winter in the northern hemisphere the polar vortex expands, directing the cold air south along the jet stream.
Bianca Feldkircher, a meteorologist for the National Weather Service, explained how a persistent blocking pattern over the Pacific Ocean combined with cold air migrating south from the Arctic – the polar vortex – created the conditions for widespread snowfall along the West Coast.
“Heat produces moisture, moisture produces storms, and heat and moisture bind to produce even more severe storms,” Feldkircher said, explaining how a warmer world is capable of causing more unstable weather.
The equatorial jet stream is also carrying warm air farther north than it used to – and it’s doing it more often, which is why the Arctic is warming faster than other parts of the Earth, melting glaciers and ice sheets that had been frozen for thousands of years – causing sea levels to rise all over the world.
The debate on whether global warming is real or not has long been over, as the weather events are measurable. In 1850 Glacier National Park had 150 glaciers, now there are about 25, which is prompting officials to consider renaming the park… and ice sheets are receding in the poles and some island nations are starting to disappear. But is this just natural climate variability or is the warming and chaotic weather created by human activities?
While scientific debate remains regarding some patterns, causal factors and outcomes, few of the world’s experts – from across multiple disciplines – dispute that climate change is human-caused; which is one reason this timeframe in Earth’s 4.6 billion-year geologic history has been academically dubbed the Anthropocene (viewed as the period during which human activity has been the dominant influence on climate and the environment).
One good place to learn more is Inside Climate News (https://insideclimatenews.org/), a Pulitzer Prize-winning nonpartisan organization that reports on what they say is “the biggest crisis facing our planet.”