NASA/Wikimedia Commons
Tim Woollings, University of Oxford
When prolonged periods of severe weather strike, two things often get the blame these days: climate change and the jet stream. Many have expressed concerns that the rapidly melting Arctic is now disturbing the jet stream, bringing more frequent bouts of wild weather. But potentially even more powerful changes are afoot in the tropics – and the consequences could be severe.
The northern hemisphere’s jet stream is a current of fast-moving air encircling the globe from west to east in the middle latitudes – the zone between the baking tropics and the freezing Arctic. The strongest winds are about ten kilometres high, near the altitudes at which planes fly, but the bottom of the jet can reach all the way down to the ground, forming the prevailing westerly winds familiar to many. The southern hemisphere’s counterpart is what gives rise to the Roaring Forties – similarly treacherous winds between latitudes 40° and 50°.
The jet forms a relatively sharp dividing line between the warm tropical and cold polar air masses. The strongest winds are concentrated in a band several hundred kilometres wide. But this band is not fixed. It meanders and snakes its way around the globe, sometimes touching the edge of the tropics and at other times scraping the polar regions
ESRL/NOAA, CC BY
As a result, the jet can have a wide array of impacts across the hemisphere. If it passes over your location, expect to be repeatedly bombarded by the whirling storms that are carried along by it. As a recent example, the severe flooding in the North of England in November 2019 arose in part from a shift of the jet, which put the UK right in the middle of a region where storms tend to grow.
If the jet shifts to pass north of you, you’ll find yourself under the warm, dry zone of the atmosphere which lies south of the jet. This brings generally settled and pleasant weather in summer, but can set the scene for droughts and heatwaves. And if the jet moves south instead, you’ll be on its cold polar side, so you’d better hope this doesn’t happen too much during winter.
Weather worries
The jet has always varied – and has always affected our weather patterns. But now climate change is affecting our weather too. As I explore in my latest book, it’s when the wanderings of the jet and the hand of climate change add up that we get record-breaking heatwaves, floods and droughts – but not freezes.
The coldest weeks of any given winter will occur when the jet brings masses of cold air directly from the polar regions. But severe though this may feel, records show that similar events in past decades were even colder than they are now. While the jet is largely doing the same as it always has, the planet-heating greenhouse gases we’ve added to our atmosphere mean that invasions of polar air these days are just that bit milder.
The flip side, of course, is that when the jet moves north in summer, bringing warm air from the south, we often have to endure temperatures beyond anything in living memory.
NASA
It is clear and well understood how climate change and the jet can combine like this to cause truly extreme weather events. But whether climate change is directly changing the jet’s behaviour is a much harder question to answer.
Some have suggested that the rapidly warming Arctic is weakening the jet, by reducing the temperature contrast between the tropical and polar air to either side of it. As a result, the jet meanders more to the north and south, and these meanders can remain fixed over one location for longer – as happened when the “Beast from the East” placed much of Northern Europe under a bitter chill.
There are certainly some interesting ideas here, but many still do not find the logic compelling, and more convincing evidence from observations and computer models will be needed for these theories to become widely accepted.
Scientists are however increasingly confident that important changes are afoot in the tropics. Driven by the vast quantities of energy pouring in from the Sun directly overhead, these are the great powerhouses of Earth’s climate. Indeed, the power of the tropics is evident in the worldwide weather disruption caused by El Niño events – subtle increases or decreases in temperatures in the equatorial Pacific Ocean, that in turn disturb the jet stream.
climate.gov
Over the past few years, it has become apparent that at high altitudes, the Earth’s tropical regions are heating up more quickly than the rest of the world. At least partly because of this, the tropical regions of the atmosphere have been widening, expanding ever so slightly away from the equator, and impinging more on the jet stream.
Tug of war
We are in the early days of a great battle in the air above our heads between the Arctic and the tropics, for the future of the jet stream. At best, there might be a stalemate, leaving the jet stream distorted but otherwise unmoved.
However, if one of the competitors outweighs the other, regional climate patterns could be severely altered as the climate zones shift along with the jet. It’s too early to say with any confidence which of these will win out, but many computer models predict the jet will shift a little towards the pole, consistent with a greater influence of the tropics.
In this case, we should expect to see the warm, dry regions at the edge of the tropics extend a little further out from the equator. The strongest impacts of this would likely be felt in regions such as the Mediterranean, which are already highly sensitive to fluctuations in rainfall. A northward jet shift would act to steer much needed rainstorms towards central Europe instead, leaving the Mediterranean at greater risk of drought.
So, the jet may not become more erratic as the Arctic warms, but it may well change profoundly. And one thing is clear: the stress of increased temperatures and altered rainfall patterns from our destabilising climate will leave us even more vulnerable to the weather patterns brought by the whim of the wandering jet stream.
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Tim Woollings, Associate Professor in Physical Climate Science, University of Oxford
This article is republished from The Conversation under a Creative Commons license. Read the original article.
HT/TonyN
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From the article: “Many have expressed concerns that the rapidly melting Arctic is now disturbing the jet stream”
What rapidly melting arctic ice? Arctic ice is not melting rapidly. This is an unproven claim which the author apparently takes as fact, demonstrating the author’s ignorance of the subject.
From the article: “The strongest winds are concentrated in a band several hundred kilometres wide. But this band is not fixed. It meanders and snakes its way around the globe, sometimes touching the edge of the tropics and at other times scraping the polar regions”
A good, simple explanation of basic jet stream movement.
From the article: “The jet has always varied – and has always affected our weather patterns. But now climate change is affecting our weather too. As I explore in my latest book, it’s when the wanderings of the jet and the hand of climate change add up that we get record-breaking heatwaves, floods and droughts – but not freezes.”
There is no evidence that human-caused climate change (that is what you are talking about isn’t it? Why not spell it out? Oh, I see, you want everyone to do like you do and assume human-caused climate change is real, so there’s no need to add in the “human-caused”. That would be redundant, wouldn’t it.)
Therefore, since there is no evidence for human-caused climate change, all the “record-breaking heatwaves, floods and droughts” you refer to must have come about as a result of natural causes (Mother Nature). Until proven otherwise. You are invited to prove that human-caused climate change is real. The truth is you are assuming things not in evidence. You are assuming too much and expecting us to believe your conclusions based on these erroneous assumptions.
It’s just amazing how many science-types don’t connect the basic dots. Human-caused climate change doesn’t cause anything because there is no evidence that it exists. Assuming it exists is self-delusion/gullibility/ignorance.
Billy Madison comes to mind
Rossby Waves anyone?
From the article: “The coldest weeks of any given winter will occur when the jet brings masses of cold air directly from the polar regions. But severe though this may feel, records show that similar events in past decades were even colder than they are now. While the jet is largely doing the same as it always has, the planet-heating greenhouse gases we’ve added to our atmosphere mean that invasions of polar air these days are just that bit milder.”
The “planet-heating” greenhouse gases we’ve added so far have resulted in a 0.4C cooling of the globe over the last three years, so where is this “planet-heating” you are claiming to see?
This author seems to be assuming the temperatures are going up, up, up. They are not. See below. You are assuming too much, sir. That’s not scientific.
The UAH satellite chart:
http://www.drroyspencer.com/wp-content/uploads/UAH_LT_1979_thru_October_2019_v6.jpg
From the article: “The flip side, of course, is that when the jet moves north in summer, bringing warm air from the south, we often have to endure temperatures beyond anything in living memory.”
Where?
Rapidly melting? If it were, Al Gore would be doing a victory lap dance.
Sadly, the media cannot or will not recognize the points in the narrative where the author departs from the educational basics to the unverified speculation. It does not help that the tone stays the same to imply that no leap has occurred.
Once upon a time, the American Southwest (and parts of Mexico) received far more rain than they do today. Then for reasons no really understands (except for the 97% consensus scientists who apparently understand everything) the rains became less frequent, lands dried up, and indigenous peoples scattered to the winds leaving only the structures of their once proud civilizations behind.
It would not surprise me at all if this has to do with colder climate versus warmer climate – all part of natural cycles. It would not surprise me that as climate generally warms (with cycles of cooling ever now and again), the American Southwest may become wetter again.
It *could* be related to the jet streams…since we didn’t have satellites orbiting the Earth back 1,200 years ago (some say that’s all Trump’s fault), we cannot really predict much about how they will behave – just speculate.
From the article: “It is clear and well understood how climate change and the jet can combine like this to cause truly extreme weather events.”
What a ridiculous statment! How can it be clear and well understood how “human-caused” climate change and the jet stream can combine when there is no evidence that human-caused climate change is real or exists?
This has got to be a mental disorder. What should we call “assuming things not in evidence, to be facts”? Delusional? Gullible? Credulous? Certainly, “ignorant”. But why? These people don’t appear to be stupid, yet they propose these unsupportable claims.
I think I have to assign most of it to groupthink. And innate intelligence doesn’t seem to be a defense against falling into this fuzzy thinking. If the groupthink goes against your innate intelligence, some people go with the groupthink, and throw their curiosity out the window. It’s easier mentally, to go with the flow, than to oppose the groupthink, for some.
More importantly, how can the interaction of the jet stream and climate change be well understood when (1) we’ve only been studying the impacts of climate change for a few decades now under circumstances where “climate” can only be quantified using many decades of measurements that are averaged to distinguish “climate” from “weather;” and (2) there are no practical applications to test your understanding of climate change, let alone its interaction with the jet stream.
Statements like this are pure BS because such asserted “understanding” can’t be demonstrated.
No freezes???? What does this look like over the next 10 days for my area, … https://www.weatherbug.com/weather-forecast/10-day-weather/douglas-city-ca-96052
The above forecast shows the 10 day at below freezing every night. Thursday night is forecast for 11 F, and that would likely be a record for this time of year.
I’ve read that over 2000 ‘lowest temperature since records began’ records were broken in the US this month. The warmers just ignore it because that destroys their argument.
Looks like Thanksgiving is going to set a record low for the day by 1 or 2 degrees for here. The two nights either side of Thursday are also going to be close to record setting at 15 F forecast. Hope I can keep my lime tree safe through this.
Wooly thinking from the University of Oxford.
The Arctic has not substantially changed since 2007.
Fantasy strawman established. Now the author will try to induce fear.
Fabricating and conflating to ensure frightening nonsense.
Jet Stream, NASA
Eight to twelve miles high in altitude, (12 km to 19 km). That lower altitude level is at the poles, while the higher altitude level is around the Equator.
The ground only reaches the stratosphere, where jet streams are found, when the mountains are high enough. That is, nowhere. Mt. Everest only reaches the 29,000 feet level, (8,840 meters); nor is Mt. Everest near the poles.
Meaning that the author above is again fantasizing.
The author’s claim:
Is totally unsupported by the author’s link to NASA. The link is to allege NASA support for the author’s preposterous claim.
Another article full of false strawmen, fantasies and fallacies.
This article was full of assertions; where is the evidence for his assertions?
Is this man the Paul Krugman of his profession?
“Rapidly warming Arctic…”
Yes, soon they will be selling time-share condos up there. Data for far less than 100 years from two or three thermometers in the Arctic. Just exactly how warm was it in 1850? No one knows, you say?
Amazing the amount of garbage that is published as news these days….
This piece sounds like an EXCUSE….
to wit: “…..if there is global COOLING, that is proof of global warming’s effect causing the jet stream to go southward”.
“The flip side, of course, is that when the jet moves north in summer, bringing warm air from the south, we often have to endure temperatures beyond anything in living memory.”
Fortunately, we have records of the heat waves of the Dust Bowl era.
“But now climate change is affecting our weather too. “
No evidence of that. The only evidence I saw was that he has a book to sell.
the climate is NOT a force, has no power and has NEVER caused even one weather event
A very important point, often missed.
Pay no attention to that ice continent at the south pole.
The storm stalled across the UK and remained almost static for 24 hours while heavy rain fell constantly it was not surprising that there were floods. The ENSO signal has been weak for the last four years does that mean that this modern warming period is over then.
Take a look at the top of the globe and see how the large pressure differentials, rotating in Polar Vortex fashion are at times spilling out into the lower latitudes. Some become meridional ridges, (Rossby waves) which interfere with the zonal circulation (Jet stream).
While the physical properties of Rossby waves have been well described in the literature, specific application to their influence on the Jet Stream have also been around for years. I recall Tim Ball writing about it in articles as much as 17 years ago and several other meteorologists since then. Even WIKI is not half bad on this one!
Postings as well as comments would greatly improve if people would take the trouble to get into some basic literature first.
Whence the Polar Vortex? That’s another interesting story.
Mental pollution: this what you suffer when you read something like this. It derails any attempt at logic. It takes a while to get your thinking back on track. It is, however, a fine example of confirmation bias.
Are the Arctic areas, really rapidly warming?
it’s when the wanderings of the jet and the hand of climate change add up that we get record-breaking heatwaves, floods and droughts – but not freezes…records show that similar events in past decades were even colder than they are now. While the jet is largely doing the same as it always has, the planet-heating greenhouse gases we’ve added to our atmosphere mean that invasions of polar air these days are just that bit milder.
So, are those the records that the past keeps getting colder, while the present remains the same? You might convince me of something, if I hadn’t seen how older records are being reduced in temperature. It seems this article, which includes no graphing, gif or other data accumulation to show how the jetstream is becoming any more wild than the past, nor any larger or slower excursions to support, well, anything, I think it’s just a writer doing his part to express “CLIMATE EMERGENCY”, which was recently discussed as the “duty” of news agencies everywhere, to take part in the Greta Thundberg Climate Disaster Telethon.
There’s nothing unusual about the recent jet-stream. It has ALWAYS had a big effect on the weather around it, it always changes & will continue to do so. Indications are it will produce a colder-than-avg winter this yr in the east-half of the US, especially starting in Jan.