Speaking of evidence, among lazy slogan-slinging alarmists nothing is more common than to hear them insist that global warming means more and more extreme weather. Supporting evidence is unnecessary, of course, it’s just something everybody knows. So we tend to take note of studies showing the opposite. This week’s example is a new study by a team of Chinese meteorologists led by Shifei Tu of Guangdong Ocean University showing, as the article title says, that there has been a decreasing trend in the destructive potential of tropical cyclones (TCs) in the Southern Indian Ocean (SIO) since the mid-1990s. In fact, the trend has been downward elsewhere in the world as well, although only in the SIO is the trend significant. But what is also significant is that nowhere is the trend upwards.
There are many ways to measure the destructive power of hurricanes. The number of storms, their durations, maximum wind speeds, size, etc. all matter. So hurricane meteorologists have come up with various measures, one of the most popular being something called the Power Dissipation Index or PDI which combines all the main parameters together into one index, the one on which these authors focus. It requires satellite monitoring to assemble complete PDI values each year so the data only go back to the 1980s.
Tu and his coauthors computed the PDI for every available year (1982 to 2021) for all the major hurricane basins around the world. The results were as follows:
What they noticed was that the PDI tended to increase early in the data set but peaked in the 1990s and has been level or dropping since then. The trend down in the SIO was statistically significant. And again, orthodoxy insists on the growing impact of human greenhouse gases on the badness of the weather so an early trend that then ends or reverses directly contradicts one of their key prediction/assumptions.
Which raises the obvious question: why? The authors note:
“The influence of environmental thermodynamic conditions is considered in order to explore a possible mechanism of influence. Previous studies have suggested that TC intensity may increase with global warming, especially TCs in the more intense categories.”
They discuss various theories that have been proposed, based on models, to predict that global warming will cause tropical cyclones to be more intense and destructive. A typical line of reasoning is that if the sea surface warms up that will translate into more destructive TCs. But, the authors note, hurricanes are very complex and their formation relies on a lot of conditions coming together just so, including some thermodynamic systems that may become less common under global warming. So there is a discrepancy between some of the theories and observations. To put it mildly.
Despite the weighty assurances of António Guterres, Al Gore and Greta Thunberg, the destructive potential of tropical cyclones is declining, not increasing.
