Global Heating, Floods and Extreme Weather

At the same time (April/May) as heatwaves are continuing across south and south east Asia there have been record breaking floods on every continent. Climate scientist Michael Mann posted on twitter that “dangerous climate change is here. It’s a question of how bad we’re willing to let it get”. Recent images of cars floating down thoroughfares in China, Europe (Germany, Netherlands) and the Middle East (Turkey, Dubai) are common on the internet and news channels. The death tolls from floods in Brazil and Kenya are in the hundreds. In Gippsland on Boxing Day we had our own flash flood in the Buchan reserve with floating cars, caravans and two fatalities.

The warnings of extreme weather events exacerbated by global warming have been with us for a long time. Twenty years ago, A. Barrie Pittock, a long time visitor to Gippsland, wrote: “small changes in average climate have a disproportionately large effect on the frequency of extreme events. This is because the nature of frequency distributions (how frequency changes with magnitude). Extremes occur at the low frequency ‘tails’ of these frequency distributions. Frequencies in these ‘tails’ change rapidly as the frequency distribution moves up or down with the average. Moreover, variability can change, and this also rapidly changes the frequency of extremes.” (Climate Change CSIRO, 2005, p.117)

Barrie Pittock continued that this “is particularly important for high rainfall events, as global warming increases the moisture holding capacity of the atmosphere, and thus preferentially increases the likelihood of high intensity rainfall.” As another way of illustrating  this the image above shows how a small move in the average of frequency distribution of the normal curves dramatically increases the ‘tail’ of extreme weather events. Similarly Barrie talks of ‘thresholds’ and ‘abrupt’ changes and it is already clear, as Michael Mann states, that some of these ‘thresholds’ have been crossed and that abrupt changes are occurring.

Another example Barrie gives of this is “the wind speed threshold for damages… [where] peak wind gust speeds show a disproportionate increase in costs when wind speeds exceed 50 knots… A 25% increase in gust wind speed above this threshold causes a 650% increase in building damages” (p.111). As with the floods, the extreme wind event across Gippsland in February probably crossed this threshold with substantial damages including some week-long power blackouts, numerous trees down and the loss of the Bairnsdale Historical Society museum roof. The towns of Metung and Mirboo North were hit particularly badly.

It hardly needs pointing out that extreme wind events are often associated with “high intensity rainfall”. Research just published states “the bigger picture is now very clear: a hotter world is likely one with higher risk of extreme floods, often driven by extreme rain from supercharged thunderstorms.” We wonder how bad it will get before governments and the populace at large, realise we are in a climate emergency and that the floods are only a small part of an enormous problem.