Like other extreme events, tropical cyclones are difficult to directly attribute to global warming. AR6. The WG1 report states that "there is low confidence in the observed long-term (40 years or more) trends in the intensity, frequency and duration of the TC [tropical cyclone] and any observed trends in tornadoes and hail... ..." However, although statistical analysis does not show a clear trend in the intensity or frequency of tropical cyclones, extratropical cyclones are another matter.

Weather patterns and storm tracks are largely controlled by global wind patterns (called cells), which are roughly organized by latitude (described in post #36). The tropical cell, called the Hadley cell (named after the lawyer and meteorologist George Hadley), circulates about 10-15 kilometers up the equator, and then circulates towards the poles, at approximately 30° N/S latitude Descend to cooler air. Here, the Hadley circulation meets the downward circulation of the Ferrer circulation, which is another circulation zone extending from approximately 30-60° N/S. Tropical cyclones are generated in Hadley Unit.

In the past fifty years, as the heat in the atmosphere has increased, the efficiency and energy content of Hadley cells have also increased. The model suggests that they may expand. This is consistent with observations of general wind patterns and storm behavior. "[I] The paths of extratropical storms in the northern and southern hemispheres are likely to have shifted to the poles, and as greenhouse gases (GHG) continue to warm, the heavy rainfall and average maximum wind speed associated with TC will increase..."

There is ample anecdotal evidence that there are catastrophic severe extratropical cyclones [ETC] in the United States: Superstorm Sandy in 2012 and Hurricane Ida in 2021 were two that swept Pennsylvania after landing in Louisiana. However, the statistical evidence is not so strong: “The overall confidence in the total number of ETCs in the two hemispheres has been low [and] since the 1980s, there has been moderate confidence in the polar movement of the storm tracks in the two hemispheres. In general, due to Inter-annual and inter-decadal changes are great, and confidence in the past century's trends in the number and intensity of the strongest ETC is also low."

Taking into account the changes in number and intensity between each year and ten years, the sample size of annual hurricanes is small enough that we cannot confidently say that they are stronger or more common than before. However, we can say that large cyclones are advancing farther to the poles than before, causing more damage to the temperate zone and increasing heat transfer from the tropics to high latitudes.

[Note: I should probably publish one more frequently: the AR6.WG1 report specifically asks not to cite it, rather than the final draft. I understand this, but I think this information is too important to be made public. After all, the report is already available here for free. )

Tomorrow: The climate in the United States is normal.

Be brave and be in good health.