- We've seen so much extreme weather recently
that it's hard to keep up with all the records
that have been broken.
In fact, in 2021, 10.6% of all weather stations
recorded record temperatures.
It's easy to blame global warming,
but extremes have not only become hotter and drier,
they've also gotten wetter, snowier, windier, and colder.
So we have to dig a bit deeper to understand
why and where these extremes are happening
so that we can prepare for what's actually coming our way.
In this episode, we're gonna explore
groundbreaking new research
that reveals one common factor
connecting almost all of these extremes,
and even suggests what we can expect in the future.
And to do this, we'll start by zooming out.
Way, way out to the troposphere.
Then we're going back in time
by drilling into Greenland's ice sheet
to uncover clues about our very uncertain future.
The changes we experience in our climate and weather
are fascinating and definitely overwhelming at times.
But the more we understand about what's happening
both today and down the road, the safer we can be.
And if you wanna see more content
on changing weather and how to prepare,
give us a like and subscribe.
Let's dive in.
(foreboding tense music)
- The jet stream is this meandering, waving, buckling
band of west-to-east moving winds
that are situated in the mid-latitudes.
And they're really important for us as humans
in our day-to-day lives because the jet stream
seems to dictate much of the weather that we experience.
So any change in weather that we have, actually,
is related to how these upper atmosphere winds are changing.
- And as we'll see, shifts in the jet stream
connect most of the extremes we saw in 2021.
The jet stream forms where warm air from the tropics
meets cold air from the poles,
and it moves weather systems from west to east
due to the rotation of the earth.
Without it we'd see far fewer changes in our daily weather.
Exactly how much effect climate change has
on the jet stream is hotly debated.
But Judah Cohen is a climate researcher
whose work focuses on this exact question.
- Strength of the jet stream is very much dependent
on how large is that temperature difference
between the equator and the North Pole.
The Arctic is warming two to three times faster
than the rest of the globe.
So that means that temperature difference
is slackening or weakening.
With the weaker temperature difference,
also the jet stream is kind of weakening or slackening.
The winds are not as fast.
Now that I think everybody agrees on,
but there are kind of this new idea
that really didn't exist 10 years ago,
that this weaker jet stream also leads
to a slower moving weather systems,
and also a more amplified or greater
waves inside the jet stream.
If the waves and the gesture have much larger
north to south extent, there's much more vigorous
mixing of air masses.
So you bring cold air from, you know,
let's say the Arctic or Alaska
bring it down to Texas and Georgia, right?
And so it's very anomalous.
You know, if it's cold in Fairbanks, they can handle it.
They're used to it.
Well if that cold, same cold air,
is quickly transported into Dallas, Texas,
or Atlanta, Georgia, you know,
they're not used to it and it causes havoc
with our infrastructure and to human lives.
- This theory may be new,
but 2021 made a pretty convincing case.
In fact, it's hard to find examples
of major weather events from last year
that aren't connected to the changes in the jet stream.
The Texas deep freeze was caused by the jet stream
becoming so wavy that it brought Arctic air
from the poles to the Southern US.
Later, the jet stream was so coiled and slow
over the Pacific Northwest,
that it trapped a high pressure system over that region
allowing hot summer sun to heat stagnant air to new highs.
A similar pattern caused flooding in Europe
and fires in Siberia.
Then hurricane Ida slowed as it hit the Gulf states,
and instead of being pushed off shore by atmospheric winds,
it was blocked by a high pressure system
and dropped record rain over the Eastern US.
- So I mean, how do we build resiliency to climate change?
And it really will come down to a large part
changes to extreme weather.
And again, extreme weather is very much
strongly connected to changes in the jet stream.
- [Presenter] Okay, and that is happening more
because of Arctic amplification, correct?
- So that you know this is a controversial idea.
That's an argument that I'm making.
- And Judah is not alone.
So we'll see in the coming years how this debate plays out,
but it's not just wind direction and speed that can change.
In fact, the entire system might be migrating,
which could mean even more significant
and long lasting changes to our climate at ground level.
Matthew Osman from the University of Arizona's
Climate Systems Center recently discovered chilling data
that suggests the jet stream is moving north.
- If we want to understand how climate change
is going to evolve in the future,
we need to understand how and why
it has changed in the past.
- Okay, so how do you figure out climate changes
and jet stream locations before satellites
were documenting them?
- [Matthew] So in this case, what my team was able to do
was to collect measurements of glacial ice
from across Greenland,
and combine those measurements together
in order to dissect properties of the climate
that are related to changes in the jet stream.
- [Presenter] By doing this, they were able to find changes
in the jet stream's position and intensity
going back 1200 years.
And they found evidence of big changes.
- Going back a thousand years into the past,
we see that changes in where it's positioned
across space can be on the order
of 10 or more degrees latitude.
So this is a lot of area that the jet stream
is covering on these really long timescales.
And this of course has big impacts on changes in weather
that we've seen over the last millennium.
- [Presenter] Over the last hundred years,
we've been emitting greenhouse gases into the atmosphere
causing the climate to warm.
And remember the jet stream is created
where warm southern air meets cold northern air.
And if the earth warms, then the place
where those air masses collide might move north
because there's less cold air.
- So what we've seen is the slight trending
of the jet stream's position towards the north
over the last 40 years,
but it hasn't been clear whether or not this is driven
by natural changes, or whether this is human caused.
- And one convincing way to separate
human cause jet stream migration
from its natural variability,
is that the jet stream's average location
goes outside of the historic range.
- And what we can do is actually compare
projected changes in the jet stream that we get from models
with the range of variability
that we see in our reconstruction.
This is essentially the range of natural variability.
And what we see is that
for high greenhouse gas emission scenarios,
we might find ourselves in a position
where the jet stream becomes effectively distinct
from the range of natural variability
within the coming decades by as early as 2060 CE.
Observations that we have from satellites
as well as estimates of the climate system
that we get from models,
both agree that the onset of changes
in the jet stream's position has already began.
It probably began about 20 years ago
in the late 20th century.
And this is really important
because when we start to think about
climate extremes, right?
So extremes and precipitation or temperature,
we care about where the edges of those variations exist.
- This is because, as the jet stream migrates
beyond the limits of its historic range,
we're likely to see even greater extremes in our climate
than we're used to.
- If we continue to emit greenhouse gases,
we will see a migration of the jet stream
further and further to the north.
And as we push the north Atlantic jet stream
outside its natural range,
we will see consequences in where the temperature extremes
as well as precipitation extremes
fall for the places where you and I live today.
- If this pattern continues to play out,
places like California and much of the American Southwest
will keep getting hotter and dryer
as the jet stream delivers less and less moisture
from the ocean.
While some more temperate regions
like the Pacific Northwest,
will receive even more moisture than they currently do.
This means many already dry regions becoming drier,
and wet regions becoming wetter.
And the same pattern would likely hold true
across much of southern and northern Europe.
Our understanding of these changes is still evolving,
but Matt and Judah's work underscores
the need for preparation.
And I, for one, feel a lot better
when I understand and when I'm ready
for what's coming our way.
For a deeper dive on how to cope,
check out our previous episodes
on drought, flooding, and winter weather.
And finally, we'd love to hear
what you think about this subject,
as well as what other weather and climate topics
you'd like for us to cover in the future.
Until next time, stay safe.
(calm foreboding music)