A reconstructed record of cyclone activity going as far back as 1850 doesn’t show what climate alarmists, with their assertions of ‘human-induced’ global warming, might have expected. The intensity question is left for future research. The researchers note that ‘For most tropical cyclone basins (regions where they occur more regularly), including Australia, the decline has accelerated since the 1950s. Importantly, this is when human-induced warming also accelerated.’ [Or so they believe.] ‘The only exception to the trend is the North Atlantic basin’. Of course detailed historical records of natural climate variation may also be hard to find.
– – –
The annual number of tropical cyclones forming globally decreased by about 13% during the 20th century compared to the 19th, according to research published today in Nature Climate Change.
Tropical cyclones are massive low-pressure systems that form in tropical waters when the underlying environmental conditions are right, says The Conversation.
These conditions include (but aren’t limited to) sea surface temperature, and variables such as vertical wind shear, which refers to changes in wind speed and direction with altitude.
Tropical cyclones can cause a lot of damage. They often bring extreme rainfall, intense winds and coastal hazards including erosion, destructive waves, storm surges and estuary flooding.
The Intergovernmental Panel on Climate Change’s latest report detailed how human emissions have warmed tropical oceans above pre-industrial levels, with most warming happening since around the middle of the 20th century. Such changes in sea surface temperature are expected to intensify storms.
At the same time, global warming over the 20th century led to a weakening of the underlying atmospheric conditions that affect tropical cyclone formation. And our research now provides evidence for a decrease in the frequency of tropical cyclones coinciding with a rise in human-induced global warming.
Reckoning with a limited satellite record
To figure out whether cyclone frequency has increased or decreased over time, we need a reliable record of cyclones. But establishing this historical context is challenging.
Before the introduction of geostationary weather satellites in the 1960s (which stay stationary in respect to the rotating Earth), records were prone to discontinuity and sampling issues.
And although observations improved during the satellite era, changes in satellite technologies and monitoring throughout the first few decades imply global records only became consistently reliable around the 1990s.
So we have a relatively short post-satellite tropical cyclone record. And longer-term weather trends based on a short record can be obscured by natural climate variability. This has led to conflicting assessments of tropical cyclone trends.
via Tallbloke’s Talkshop
June 28, 2022 at 04:32AM