SOMETHING NEW TO WORRY ABOUT--QUASI-RESONANT AMPLIFICATION

Picture a river flowing down from the mountains to the plains. In the high country, where the river's descent is steep and hedged in by canyon walls, it's likely to follow a relatively straight path, basically tracing the shortest route down. Once it gets to the plains, however, there's no big difference between one path and another, and the river will begin to meander.

 Meandering river

Credit: Alana Whitman

Something similar is true for the jet streams, vast rivers of air that circle the globe from west to east, sometimes reaching speeds of 250 miles per hour. Like rivers, jet streams typically meander north and south. The size of those meanders and the speed with which they gradually drift eastward have major impacts on the weather. The UK, for example, was deluged by record floods in 2007 and again in 2012 when the jet stream looped far to the south and then stalled, unleashing extended periods of heavy rains.

Meandering polar jet stream

Credit: NASA/Goddard Space Flight Center 

That, in turn, gets us to climate change and quasi-resonant amplification (QRA). 

One of the most dramatic impacts of global warming and climate change is that the far north and south are warming much faster than the mid-latitudes and the tropics, a phenomenon known as polar amplification. What this means is that the temperature difference between the poles and the tropics-- which is what creates and drives the jet streams--is reduced. And like a river crossing a plain, this reduced gradient lets the jet stream meander farther north and south, and also tends to make the individual loops, known as Rossby waves, drift more slowly from west to east.

At the extreme, the meanders in the jet stream can form a stable sequence of exaggerated loops around the planet that can stay in place for weeks or months. This is known as quasi-resonant amplification  (QRA) and its results can be devastating. Warm, sunny days can extend into deadly heat waves, droughts and wildfires; while cool, rainy weather can linger, drenching an unlucky region with unprecedented rains and floods.

Michael Mann, a distinguished professor of atmospheric science and Pennsylvania State University, says that as of 2018 this phenomenon has now passed from the theoretical to the all-too-real and threatening. "It played out in real time on our television screens and newspaper headlines in the form of an unprecedented hemisphere-wide pattern of extreme floods, droughts, heatwaves and wildfires," he says.

Unfortunately, Mann adds, climate models indicate that such QRA-caused weather extremes will grow more frequent and more severe unless we get a handle on global warming. Recent research reinforces the link between reduced Arctic sea ice and the meandering jet stream, along with equally dire predictions. We can hope that humanity (and the politicians and corporations who hold the reins) will get their act together. In the meantime, however, we can all expect more QRAs and the devastating weather extremes they bring coming to a region near us.

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You can read an earlier post on this subject here.

For more detail on arctic warming and its impacts on our weather click here.

And for a new study that shows that these destructive "blocking events" will cover greater areas as the world heats up, navigate to this URL.

(As-yet unpublished research shows that these stalled atmospheric waves have the potential to cut crop production across much of the northern hemisphere.)

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SCIENTISTS CAN NOW LINK WEATHER EXTREMES TO CLIMATE CHANGE

Climatologists have traditionally been leery of linking a specific event--an extended drought, an exceptional run of hurricanes, massive flooding--to climate change. The most they could be coaxed to say was something along the lines that climate change might have increased the odds of the extreme event, often with a comparison to rolling loaded dice or to an athlete on steroids.

Recently, however, some researchers have started to be more specific. For example, Frederika Otto, a climate scientist at Oxford University, and her colleagues recently reported that South Africa's three-year mega-drought, during which Cape Town came nerve-wrackingly close to running out of water, was demonstrably three times as likely as it would have been without human-caused climate change.

This new capability goes beyond just pinning down the increased odds of an extreme event. In three cases recently, researchers have felt confident enough to say that certain events simply could not have happened without human climate forcing. These included devastating heatwaves in Asia in 2016, the global heat record set the same year, and shockingly high sea temperatures in the Gulf of Alaska and the Bering Sea between 2014 and 2016. 

A review of 170 similar attribution studies between 2004 and 2018 found that two-thirds of the extreme weather events studied were more likely or more intense because of human caused climate forcing.

 South Africa's Theewaterskloof Reservoir, nearly empty on March 11, 2018

Credit: Zaian

So the question is, what's changed? Why are climate scientists now able to make such specific attributions of the impacts of human-caused climate change?

In principle, the answer is remarkably simple. Researchers use multiple state-of-the-art computerized climate models to run thousands of simulations with slightly different initial conditions. Some of the simulations run with current levels of greenhouse gas levels while others use pre-industrial levels. The researchers can then see how many times a comparable event shows up in each scenario. A drought as long and intense as the one that drained Cape Town's reservoirs to the brink of catastrophe happened three times more often under current atmospheric greenhouse gas levels than in models using pre-industrial levels.

In practice, it's a bit more challenging. The multiple computer simulations that are needed are costly and need a lot of time even on the fastest supercomputers. Otto and her colleagues got around this by tapping into weather@home, a network of thousands of volunteers who offer up time on their computer to help perform these massive calculations. In addition, current climate models are not fine-grained enough to model smaller events, such as a crop-destroying hailstorm or an outburst of tornadoes.

Still, scientists now have what it takes to specify to what extent many extreme events, such as a drought, massive flooding or a killer heat wave, can reliably be attributed to human-caused climate change. We can expect much more frequent, accurate and meaningful reports of this kind in the near future.

These attribution studies are not likely to convince dyed-in-the-wool climate change deniers, but they are already proving helpful to planners at all levels. For example, Helen Davies, with the Western Cape's Department of Economic Development and Tourism, now knows that the devastating drought was not a once-in-a-lifetime event. "This is an incredibly strong message which we cannot afford to ignore. We may need to work on a radically new approach to water management."

Otto hopes that this approach will soon be fast and accurate enough to be linked to extreme weather events in real time. Germany may become one of the first countries to do this on a regular basis. 'It’s part of our mission to illuminate the links between climate and weather,” says Paul Becker, Vice President of the German Weather Agency. “There is demand for that information, there is science to provide it, and we are happy to spread it.”

One example of real-time attribution is the assessment by scientists at the Lawrence Berkeley National Laboratory that Hurricane Florence is 50 miles wider and will inundate the Atlantic Coast with 50 percent more rain than a comparable hurricane before human-caused climate change.

And a new study using the supercomputers at the Lawrence Berkeley National Laboratory was able to detail the additional rainfall provoked by global warming in 15 hurricanes that took place in the last ten years, and predict even more rainfall and more intense winds if warming continues.

Let's hope that the entrenched climate change denial on the part of the current US president and congress does not keep this important emerging science from being used here at home.

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The Nature article from which most of this information comes can be found here.

The article summarizing 170 different studies, including a useful interactive map, can be found at this URL.

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SIGNS OF THE TIMES: PROFESSORS OF CYBERPSYCHOLOGY AND EXTREME-WEATHER RISKS

My email today included notices of two new academic posts that I found eye-opening:

KIT, the Karlsruhe Institute of Technology, in Germany, has endowed a new professorship dedicated to the study of the risks from extreme weather events. I guess they haven't been convinced by the arguments of climate-change deniers.

Tornado, Andarko Oklahoma, May 1999/Credit Dizpics1/Wikipedia
Intense, large-scale tornado outbursts like this are happening more frequently

The University of Warwick, in the UK, has appointed its first cyberpsychologist, Monica Whitty. Professor Whitty joins other researchers at the university's Cyber Security Centre. Her focus is "on the human element . . . behaviour online to identify cyber criminals and in turn protect people from becoming victims."

Maybe if Hillary Clinton had known about Dr. Whitty a year or two ago, we'd have a different person taking the oath of office on January 20.