Extreme Weather #1 – Long term trends in Frequency and Intensity of Landfalling Tropical Cyclones
The latest IPCC report, AR6, was released in draft form in 2021 and in what seemed like an approved released form early 2022. You can download each chapter from ipcc.ch (Working Group 1 is “the physical science basis”).
Chapter 11 covers extreme events – “Weather and Climate Extreme Events in a Changing Climate”.
Here’s the simple version of what they say about long term trends in tropical cyclones (severe tropical storms):
For long term trends of landfalling tropical cyclones, we have a data quality issue. We do have good data for the USA going back to 1900 and there’s been no increase. We do have good data for Australia going back to the late 1800s and there’s been a decrease. On a global basis the data quality isn’t good enough to have any confidence in trends in intensity or frequency.
The actual text, from p. 1585-1586, is in the Notes at the end of this article.
This how the executive summary for the chapter captures the essence of this apparently good news, p.1519:
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That’s the main dish.
Here’s an extract from Thomas Knutson et al 2019:
One of their summaries:
In summary, no detectable anthropogenic influence has been identified to date in observed TC- landfalling data, using type I error avoidance criteria. From the viewpoint of type II error avoidance, one of the above changes (decrease in severe landfalling TCs in eastern Australia), was rated as detectable, though not attributable to anthropogenic forcing (9 of 11 authors), with one dissenting author expressing reservations about the historical data quality in this case.
It’s important to note that landfalling TCs are only a small subset of TCs that form out over the ocean, and in the next article we’ll look at this.
Notes
Text of AR6 from p. 1585-1586 about long term trends in tropical cycles:
Identifying past trends in TC metrics remains a challenge due to the heterogeneous character of the historical instrumental data, which are known as ‘best-track’ data (Schreck et al., 2014). There is low confidence in most reported long-term (multi-decadal to centennial) trends in TC frequency- or intensity-based metrics due to changes in the technology used to collect the best-track data. This should not be interpreted as implying that no physical (real) trends exist, but rather as indicating that either the quality or the temporal length of the data is not adequate to provide robust trend detection statements, particularly in the presence of multi-decadal variability..
..A subset of the best-track data corresponding to hurricanes that have directly impacted the USA since 1900 is considered to be reliable, and shows no trend in the frequency of USA landfall events (Knutson et al., 2019)…
..A similarly reliable subset of the data representing TC landfall frequency over Australia shows a decreasing trend in Eastern Australia since the 1800s (Callaghan and Power, 2011), as well as in other parts of Australia since 1982 (Chand et al., 2019; Knutson et al., 2019). A paleoclimate proxy reconstruction shows that recent levels of TC interactions along parts of the Australian coastline are the lowest in the past 550–1500 years (Haig et al., 2014).
References
Seneviratne et al, 2021: Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
Knutson, T.R. et al., 2019: Tropical Cyclones and Climate Change Assessment: Part I: Detection and Attribution. Bulletin of the American Meteorological Society