Rare event that amplified fires in Australia in 2019 is not expected to happen again
This article is adapted from a research brief by the ARC Center of Excellence for Climate Extremes. Find the original here. The authors, Martin Jucker of the ARC Center of Excellence for Climate Extremes and Thomas Reichler of the University of Utah, are co-authors of the study.
In the southern hemisphere spring of 2019, generally very strong winds in the stratosphere, around 186 mph (300 km / h) at a height of 18.6 miles (30 km), almost completely collapsed within days – a So-called Sudden Stratospheric Warming (SSW) was underway. These high atmospheric events are known to influence the surface wind structure and cause abnormal weather conditions on the ground. The stratosphere affects surface weather and climate on a global scale, and the ongoing global warming is causing major changes in this influence.
This is why, at the beginning of September, the The stratospheric research community has argued that something very rare is happening and could make matters worse.
Unfortunately, the researchers were right.
Spring 2019 has been exceptional for Australia: scorching heat, the culmination of a three-year drought and bushfires raging much earlier in the season than at any time in history. In the summer, the fires and the loss of flora, fauna and human life, as well as the impacts on respiratory health, were on a catastrophic scale. While the reasons for this devastating natural disaster were many and are still the subject of intensive research, a new study Geophysical research letters shows how rare one of the major contributors to this extreme fire weather was and how, in a hotter future world, it will become even rarer to the point of being nearly impossible.
Interestingly, Australia’s usual weather suspect of fires, the El Niño Southern Oscillation (or ENSO) did not do much that year. But in 2019, there was another factor: a strongly negative Southern Ring Mode (SAM), which is known to be linked to the hot, dry conditions over eastern Australia. The SAM can be flown by many different things, but in 2019 the obvious driver was indeed very rare.
Sudden stratospheric warming
However, SSWs are much more common in the northern hemisphere than in the southern hemisphere. In the north, SSWs occur at irregular intervals, but on average every two winters. The winters 2017-18 and 2018-19 saw SSWs, and one event in January 2021 lasted until February.
SSWs affect the weather over all of the high northern latitudes. They create extremely cold conditions over the North Atlantic, Northern Europe and Asia, while the eastern Canadian Arctic tends to be warm. SSWs are also bringing more storms to southern Europe, increasing the risk of flooding in the Mediterranean, while parts of Scandinavia and the British Isles tend to experience drought. These conditions last up to two months, which is of great practical importance as they help scientists make weather forecasts sometimes beyond the regular 7-10 day forecast.
It’s the global impacts that make SSWs so interesting. Scientists all over the world seek out SSWs, creating opportunities for international collaborations. For example, this work represents a collaboration between the University of Utah, the University of New South Wales in Australia and Johns Hopkins University in Baltimore.
An SSW has only been recorded once before in the southern hemisphere, in the spring of 2002 (which was also followed by fires that summer). What we do know from climate models is that events like these are usually followed by hot, dry conditions in Australia, and these conditions prevail for many months (e.g. in the southern hemisphere summer ).
But since this had only happened for the second time, it was impossible to say How? ‘Or’ What this event was rare and, most importantly, we did not know if this frequency would change with climate change. Was this second event after 2002 the result of climate change? Does that mean we should expect this to happen more? The only reliable measurements of the stratosphere come from satellites, and they have only existed since the late 1970s. Before that, balloon measurements give us an indication that nothing similar has happened since the 1950s. this we have no idea.
Modeling of the stratosphere
Running climate models that include a good representation of the stratosphere is very expensive, but people didn’t think it was important to do these surveys, at least in relation to what the oceans and other things are doing in the world. local climate and weather. As a result, the climate model simulations we had of this part of the atmosphere were generally unreliable or just too short.
That’s why we used a really good climate model for a long time – 9,900 years to be precise (the time simulated, not the time it took us to run it) at the Center for High Performance Computing (CHPC) in read.
The generous IT support of the U CHPC was absolutely crucial for this research. The climate model simulations took several years of computing time and created terabytes of data. While the data is now stored in an external IT facility, the analysis of the large amount of data is carried out entirely at CHPC. These simulations have also served as the basis for several other scientific publications.
With this simulation, we were able to determine how many times events like 2019 would have happened. We found that they would have occurred about once every 22 years under conditions similar to 1990. This fits well with the 17 years between the sudden stratospheric warming events of 2002 and 2019. However, we also found that in the future (a world similar to 2080), due to greenhouse gas emissions, these events tend to decrease rapidly, occurring about once every 300 years.
We’re already one-third of the way to 2080 (since 1990), so these stratospheric events in the southern hemisphere are already happening less frequently than once every 22 years. So what will the world be like 300 years from now if this is the next time an SSW event in the Southern Hemisphere occurs? Probably nothing like 2021 (remember the year 1721?), But it is likely that until another such event occurs we will have to deal with many more catastrophic events related to the climate change. All in all, it might be better to have a few more SSW events and learn how to deal with them than to deal with the consequences of climate change. But the stratosphere still influences our weather, whether there is SSW or not.
Find the full study here.