A new paper advances our understanding of the link between anthropogenic global warming and the apparent uptick in severe weather events we’ve been experiencing. Let’s have a look at the phenomenon and the new research.
Climate Change: The Good, The Bad, and the Ugly.
It is mostly bad. Sometimes it is ugly. I was looking at crop reports from the USDA and noticed an interesting phenomenon in Minnesota, that is repeated across much of the US this year: Fewer acres are in crops but among those acres that are planted there is a high expected per-acre yield. The higher yield will make up for the lost acreage this year. Unfortunately, that is about as good as it gets.
The lost acreage, at least in Minnesota as I understand it, comes from a late spring followed by a wet early summer. And holy crap was it wet, and fairly cool. My own tomatoes were utterly confused. One plant produced a single tomato that ripened a month and a half early, then waited for weeks to make its next move. I think organisms do that sometimes; when they think they are about to die they reproduce desperately, which for a tomato plant, is producing one premature tomato and then trying to not be noticed for a while. In any event, many Minnesota farmers live with an interesting conflict. There are parts of their farms they can’t plant in a given year because it stays too wet too long, and that varies from year to year. The rest of the farm is irrigated much of the summer. This year, it seems that there has been enough extra rain to increase productivity of the irrigation season, but acreage was lost between the encore of a sort of Polar Vortex mimic and a lot of rain.
- See: Minnesota’s Amazing June Weather and Minnesota’s Current Weather Disaster — Don’t worry we’ll be fine.
The extra productivity was a lucky break, and is limited in its effects. The same weather phenomenon that made June nearly the wettest month ever in the upper plains has contributed significantly to a longer term drought in California, which is on the verge of ruining agriculture there. Severe flooding or extreme dry can do much more damage to agriculture than is accounted for by minor increases in productivity because of the extra water vapor provided by Anthropogenic Global Warming.
And the floods can be downright dangerous. I was talking to my friend and former student Rusty several months ago about the flooding in Colorado. I asked her about how her husband was doing (they both happen to be climate scientists by the way).
“Oh he’s probably fine but I’ve not heard from him in three days. His cell phone battery is probably out. I imagine he’s clinging to some high ground up on the Front Range about now.”
He is a volunteer first responder and had headed up into the canyons year boulder during the big floods there. Which were like the big floods in Calgary. And Central Europe. And the UK. And that rainy June here. And the flooding that just happened in several parts of the US.
All of it, all of those floods, and some significant drought, and the Polar Vortex that hit the middle of North America last winter, all caused, almost certainly, by the same phenomenon.
Wildfires are probably enhanced by recent weather phenomenon as well, with extreme rains causing the build up of fuel, followed by extreme dry providing the conditions for larger and more frequent fires.
On the more extreme end of effects for severe weather is the Arab Spring phenomenon. It is one thing to have a bad year for corn because of a wet spring. It is worse to have a multi year drought that could seriously affect our ability to buy almonds, avocados and romaine from California. But what happens when an agricultural system fails for several years in a row, the farmer abandon the land and move to the cities where they become indigent, a civil war breaks out, and next think you know a Caliphate is formed, in part on the wreckage of one or two failed regimes, failed in large part because of severe weather conditions caused by human induced climate change?
- *See: 500,000 people evacuate massive 2-week long flood; 40+ dead, Don’t forget Canada’s memorable storm, Today’s Weather Icestorm Noreaster Flooding Ruh Roh, and UK Hammered, not in a good way.
I’ve discussed this at length before. (See: Linking Weather Extremes to Global Warming and Global Warming and Extreme Weather) The relationship is pretty simple, to know how it works all you have to do is remember one word:
AGWAAQRaRWaWW. Rhymes with “It’s stuck in my craw, paw!”
Let me parse that out for you.
AGW -> AA -> QR-RW -> WW
AGW – Anthropogenic Global Warming
Anthropogenic global warming (AGW) is caused mainly by added CO2 in the atmosphere from burning fossil fuel. By definition, the burning of fossil fuels is the release of energy by separation of carbon previously attached to other atoms by biological processes typically a long time ago, and over a long period of time. We humans are spending a century or two releasing tens and tens of millions of slow storage of Carbon, all at once in geological time, causing the chemistry of our atmosphere to resemble something we’ve not seen in tens of millions of years.
AA – Arctic Amplification
The CO2 by itself would warm the Earth to a certain degree, but it also produces what are called positive feedbacks. Which are not positive in a good way. For example, added CO2 means there is more water vapor in the atmosphere (because of more evaporation and ability for the atmosphere to hold water). Water vapor is, like CO2, a greenhouse gas. So we get even more warming. In the Arctic, there are a number of additional positive feedbacks that have to do with ice. The Arctic, with its additional positive feedbacks, warms more than other parts of the planet. This is called Arctic Amplification.
QR-RW – Quasi-resonant Rossby waves
Normally, heat from the equator makes its way towards the poles via air and sea. Giant currents of air are set up by a combination of extra equatorial heat and the rotation of the earth. Part of this system is the so-called “trade winds” (winds that typically blow in a typical direction) and the jet streams.
The jet streams occur at high altitude between major bands of trade winds that encircle the earth. The trade-wind/jet stream systems are typically straight rings that encircle the earth (a bit like the bands on the major gas planets) and the jet streams move, normally, pretty straight and pretty fast. But, with the warming of the Arctic, the differential between the equator and the poles is reduced, so all sorts of strange things happen, and one of those things is the formation of quasi-resonant Rossby waves.
A Rossby wave is simply a big giant meander in the jet stream. Quasi-resonant means “almost resonant” and resonant means that instead of the meanders meandering around, they sit in one place (almost).
It appears that Quasi-resonant Rossby waves set up when there is a certain number (roughly a half dozen) of these big meanders. When this happens, the jet stream slows down. The big bends in the jet streams block or stall weather patterns, and the slow moving nature of the jet stream contributes to the formation of either flash droughts (as Paul Douglas calls them) where several weeks of nearly zero rain menace a region, or extensive and intensive rainfall, like all the events mentioned above.
WW – Weather Whiplash
That’s the term that refers to dramatic shifts between the extreme weather events created by Quasi-resonant Rossby Waves, the result of Arctic Amplification, caused by Anthropogenic Global Warming.
And that’s how you get yer AGWAAQRaRWaWW. Rhymes with “It’s stuck in my craw, paw!”
Quasi-resonant circulation regimes and hemispheric synchronization of extreme weather in boreal summer
Which brings us to Quasi-resonant circulation regimes and hemispheric synchronization of extreme weather in boreal summer. This is the title of a paper by Dim Coumou, Vladimir Petoukhov, Stefan Rahmstorf, Stefan Petri, and Hans Joachim Schellnhuber. Here is the “for the people” abstract of the paper:
The recent decade has seen an exceptional number of boreal summer weather extremes, some causing massive damage to society. There is a strong scientific debate about the underlying causes of these events. We show that high-amplitude quasi- stationary Rossby waves, associated with resonance circulation regimes, lead to persistent surface weather conditions and therefore to midlatitude synchronization of extreme heat and rainfall events. Since the onset of rapid Arctic amplification around 2000, a cluster of resonance circulation regimes is ob- served involving wave numbers 7 and 8. This has resulted in a statistically significant increase in the frequency of high- amplitude quasi-stationary waves with these wave numbers. Our findings provide important new insights regarding the link between Arctic changes and midlatitude extremes.
The effects of climate change have occurred (and will occur) on a number of time scales. Over a century we’ve had a foot of sea level rise, which is showing its effects now. Storminess, in the form of changes in tornado regimes and tropical storms, has probably been with us for a few decades. But Agwaaqrarwaww has probably only been with us since about the beginning of the present century.
I blogged about this before. In “Global Warming And Extreme Weather” I described an earlier paper produced by the same research team, in which they presented this graphic:
I sent that to one of the authors, which may have inspired the production of a different graphic but showing the same trend, for the current paper:
Look how recent this phenomenon is. It is now, current, happening at sub-climate time scales. We don’t know enough about it, and we need to address it.
I asked Stefan Rahmstorf, one of the paper’s author and the scientists I was exchanging graphics with, to elaborate on the signficance of this recent study and to explain why it is important. He told me, “Previous studies have failed to find trends linked to global warming which could explain the recent spate of unusual extreme events. For example they have looked at trends in the occurrence of blocking or in the speed of the jet stream. But you need to know what you are looking for in order to find it. The planetary wave equation reveals what the resonance conditions are which make the waves grow really big, causing extreme weather. So we knew what trends to look for.”
I also asked him if severe weather events post dating the end of his study period conform to expectations as Rossby Wave events. “I can’t say for sure because we have not done the analysis for the very latest data yet – studies like this take time,” he told me. “But I suspect there have been more resonance events. They are not necessarily constrained to July and August either. The record flooding in May/June 2013 in Germany of the Danube and Elbe rivers, for example, was associated with large planetary wave amplitudes. Dim Coumou has assembled a young research team now that will work on further data analysis.”
Damian Carrington has written up this research at the Guardian, and notes:
Prof Ted Shepherd, a climate scientist at the University of Reading, UK, but not involved in the work, said the link between blocking patterns and extreme weather was very well established. He added that the increasing frequency shown in the new work indicated climate change could bring rapid and dramatic changes to weather, on top of a gradual heating of the planet. “Circulation changes can have much more non-linear effects. They may do nothing for a while, then there might be some kind of regime change.”
Shepherd said linking the rise in blocking events to Arctic warming remained “a bit speculative” at this stage, in particular because the difference between temperatures at the poles and equator is most pronounced in winter, not summer. But he noted that the succession of storms that caused England’s wettest winter in 250 years was a “very good example” of blocking patterns causing extreme weather during the coldest season. “The jet stream was stuck in one position for a long period, so a whole series of storms passed over England,” he said.
I’m not convinced that the seasonality of Arctic Amplification matter much here, and I note that we’ve not looked closely at the Antarctic. Also, “blocking patterns” and QR waves are not really the same exact thing. They may be different features of the same overall phenomenon, but QR Rossby Waves are a more general phenomenon, and a “blocking” is something that happens, probably, when that phenomenon interacts with certain kinds of storms.
It occurs to me that there is a huge difference between Agwaaqrarwaww happening randomly in space vs. blocking and steering waves setting up for long periods of time over the same place, and appearing in those places typically. Like Godzilla. We know that over time Godzilla will usually destroy Tokyo and not London, because Godzialla, while sometimes random, is usually geographically consistant. Can we expect Rossby Waves to usually causae drought in California, flooding on the Front Range or Rockies, and drenching rains in the Upper Midwest and Great Lakes Region, for example? I asked Stefan about that as well.
“We have not looked at this aspect yet, but the recent paper by Screen and Simmonds has indeed found such a preference of the wave troughs and crests to sit in certain locations.