CHANGE IN WEATHER EVENTS
By Masooma Amjad Khokhar
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 temperatures. It's easy to blame global
warming, but extremes have not
only become hotter and drier, but 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 blog, we're going to 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 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 what's
happening both today and down the road, the safer we can be. Let's dive in. 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 we know one
researcher “Judah Cohen” that is a climatic researcher whose work focuses on this
exact question. The strength of the jet stream is very much dependent on how large
is the 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 the 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, but there is some
kind of this new idea that really didn't exist 10 years ago, that this weaker
jet stream also leads to slower-moving weather systems, and also a more
amplified or greater wave inside the jet stream. If the waves and the gesture
have a much larger north-to-south extent, there's a much more vigorous mixing of
air masses. So you bring cold air from, you know, let's say the Arctic or
Alaska brings 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 the 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 offshore 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 strongly connected to changes in the jet stream. 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 to dissect properties of the climate that are
related to changes in the jet stream.
Source: www.discovermagazine.com
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 there are many areas where the jet stream is covering these really long timescales. And this of course has a big impact on weather changes that we've seen over the last millennium.
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 begun. 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, some places will keep getting hotter and dryer
as the jet stream delivers less and less moisture from the ocean. Due to
climatic changes many already dry regions becoming drier and wet regions
becoming wetter. 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 my blog “Facts about climatic change”. 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 so don’t
forget to comment below. Until next time, stay safe and calm.
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