[editor’s note, I do appreciate the irony in this post following the previous one Time to Pack a Bug-Out Bag, Hurricane Season from Hell Predicted but a single year is irrelevant to long term trends.]
by John Shewchuk
Tropical cyclone data from global sources show that tropical cyclone activity is slowly decreasing during [a period of] global warming. Unfortunately, there seems to be very little (if any) literature explaining why this is happening. This paper attempts to address this issue. For the remainder of this paper, named global tropical cyclones will simply be referred to as hurricanes.
Figure 1 shows hurricane activity from 1980 to 2023. The light grey linear trend line reflects the slow trend of decreasing hurricane activity.
Figure 1. Global hurricanes (Categories 1 to 5) from 1980 to 2023, with a 5-year centered weighted smoothing filter, and a thin grey linear trend line. Data source: https://tropical.atmos.colostate.edu/Realtime/index.php?arch&loc=global
Unlike mid-latitude polar front storm systems which depend on horizontal temperature gradients for storm growth, tropical thunderstorms, which are essential for hurricane formation, are more dependent on vertical temperature gradients. This study shows that global warming is weakening tropical vertical temperature gradients and the hurricane growth environment.
The United Nations’ Intergovernmental Panel on Climate Change (IPCC) climate models have been predicting that global warming will warm the tropical upper troposphere faster than the lower troposphere. John Christy and Richard McNider investigated these IPCC forecasts by using radiosonde (weather balloon) sounding data which confirmed that the tropical upper troposphere was indeed warming faster than the lower troposphere.1 The results of their study can be seen in Figure 2 as a dashed line. The author performed another study using only radiosonde data from oceanic regions between latitudes 5 and 25 degrees (north and south); and only for the 5 months of maximum hurricane activity (NH: Jul-Nov, SH: Dec-Apr) which is why this study found trend data that is almost twice as large as the Christy & McNider study. Except for Hong Kong, only island station data were used to best represent hurricane formation regions where more than 90% of hurricanes develop. The solid line in Figure 2 shows these results. Atmospheric cooling is observed above the tropopause.
Figure 2. Pressure-level temperature trends. The DAHSED profile represents data extracted from the Christy & McNider (2017) study which analyzed four radiosonde datasets (1979-2016) over the tropical region 20N to 20S. The SOLID profile represents 15 radiosonde stations from island stations between 5 and 25 degrees latitude (north and south) which had both 00Z and 12Z sounding data for the years 1980 and 2023 for the primary hurricane formation months (NH: Jul-Nov, SH: Dec-Apr).
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1 Christy, J.R. and R.T. McNider, 2017: Satellite bulk tropospheric temperatures as a metric for climate sensitivity. A-P J. Atmos. Sci., 53(4), 1-8, DOI:10.1007/s13143-017-0070-z.
Table 1 lists the 15 island stations (except Hong Kong) used for this study, which resulted in the solid profile line seen in Figure 2, above.
Table 1. Upper-air sounding locations (that have both 1980 and 2023, and 00Z and 12Z sounding data) from island stations between 5 and 25 degrees (north & south) latitude.
The tropospheric vertical temperature slope (also called the vertical temperature gradient) is critical for convection. A stronger vertical temperature gradient, means a larger temperature difference between the upper and lower levels of an atmospheric layer – such as the troposphere. The greater the vertical temperature difference, the greater the temperature gradient, and the greater the potential for convection. Convection is necessary for thunderstorm growth and the early stages of hurricane growth.
While there are other atmospheric and thermodynamic processes involved with hurricane development, only the tropical vertical temperature gradient is studied here. Specifically, the tropical troposphere’s Convective Available Potential Energy (CAPE) is examined. CAPE is a function of the atmosphere’s vertical temperature gradient and indicates the potential for convection. Higher CAPE levels indicate greater thunderstorm potential, while lower CAPE levels indicate reduced thunderstorm potential.
Composite soundings from hundreds of 1980 and 2023 sounding profiles were created by the RAOB Program (www.raob.com). RAOB was also used to calculate CAPE and plot the composite soundings in Figure 3.
Figure 3 shows the results of this study. It shows two composite sounding profiles: a 1980 composite sounding (blue) and a 2023 composite sounding (red). The mean CAPE values were produced from an average of three CAPE calculations: surface based (SBCAPE), mixed layer with 25 mb depth (MLCAPE/25), and mixed layer with 50 mb depth (MLCAPE/50). Results show that the upper tropospheric warming reduced CAPE values by 17%. The reduction in CAPE reduces the potential for tropical thunderstorm growth, which inhibits the early stages of hurricane development, and thus helps explain why hurricane activity is decreasing during global warming.
Figure 3. Pressure level temperature trend comparison and associated CAPE differences between 1980 (Blue) and 2023 (Red) composite profiles from 15 tropical island stations between 5 and 25 degrees latitude (NH: Jul-Nov, SH: Dec-Apr). Mean CAPE values are an average of three CAPE calculations: Surface based (SBCAPE), mixed layer w/25 mb depth (MLCAPE/25), and mixed layer w/50 mb depth (MLCAPE/50).
Story Tip
China’s Flag Is Red, Not Green
https://www.wsj.com/articles/chinas-flag-is-red-not-green-emissions-water-pollution-coral-reefs-1d9fc481
China started caring about their environment about ten years agp.
What they cared about was urban air pollution. Not CO2.
New cleaner coal power plants are part of the solution. It is CO2 emissions China does not care about, just real air pollution.
Not much progress in the past ten years but at least the urban air pollution stopped increasing.
Our friend’s son pilots a Michigan corporate private jet to China frequently and reports on the progress. Or lack of progress. He watched the Chinese air pollution increase for 20 years before it leveled off about a decade ago.
The Guardian says hurricanes are becoming more intense. Models say it because of GHG emissions.
– – – – – – – – –
Hurricanes are intensifying more rapidly – and the most vulnerable communities are hit hardest
Hurricanes are more frequently escalating quickly, and the places they destroy may be those disadvantaged by racist housing policy
https://www.theguardian.com/us-news/2024/mar/07/hurricane-strength-global-warming-intensification
Observed increases in North Atlantic tropical cyclone peak intensification rates
Quickly intensifying tropical cyclones (TCs) are exceptionally hazardous for Atlantic coastlines. An analysis of observed maximum changes in wind speed for Atlantic TCs from 1971 to 2020 indicates that TC intensification rates have already changed as anthropogenic greenhouse gas emissions have warmed the planet and oceans.
https://www.nature.com/articles/s41598-023-42669-y
The Guardian and Nature articles are not credible. The first ignores rapidly weakening cyclones while the second actually grays-out weakening cyclone data — so you can’t see what they are hiding.
I know the Guardian is an alarmist rag. But unfortunately, a huge amount people take it as the truth. And don’t forget, hurricanes are racist. 😉
The satellite images always show the clouds as “white” so maybe you’re on to something! 😎
The Guardian is very reliable if you reverse everything they claim by 180 degrees. They would print a climate chart upside down if that would help the global warming crisis narrative.
The narrative around hurricanes has huge uncertainty built in and fortunately for the alarmist fraternity few people check hurricane data.
“”…tropical cyclone activity is slowly decreasing during [a period of] global warming. “”
But the media is telling people…
“”Hurricanes are intensifying more rapidly – and the most vulnerable communities are hit hardest”” https://amp.theguardian.com/us-news/2024/mar/07/hurricane-strength-global-warming-intensification
BBC Verified / sarc
Hurricanes can be fickle.
Maybe they’re pissed that some are given male names?
For the sake of inclusivity, isn’t it about time we had a transgender hurricane?
Hurricane Mulvaney?
(Look what it did Bud-Lite!)
Climate alarmism is simply hot air.
Nice post. First I had heard about CAPE. Makes sense.
CAPE is a key analysis parameter in the meteorologists’ toolbox, especially for thunderstorm potential.
Wow ???? You must not comprehend stuff you read. Or your memory is failing.
https://wattsupwiththat.com/2022/07/23/ocean-atmosphere-response-to-solar-emr-at-top-of-the-atmosphere/
You even made comments. On that post.
Standard SkewT diagram training for pilots, meteorologists…never mentioned by CliSci types…
https://www.weather.gov/source/zhu/ZHU_Training_Page/convective_parameters/skewt/skewtinfo.html
The Ventusky weather map website has an option to display the CAPE index under their Thunderstorms view.
Can also be found at “earth.nulschool(.)net”
Maybe lighten up on the booze.
Welcome to something I wrote HERE about 17 years ago.
Any tiny increase in the warmth of the air at higher altitudes causes a near squared decrease in the power differential that drives these storms. Why “near” squared? Not a flat Earth.
Although CAPE is important, if there is significant shear in the atmosphere, a storm will not develop or at least be hindered from realizing full potential. A study in the trends of shear would be both useful & potentially enlightening
It would be better to split the hemispheres.
As the peak solar intensity increases in the NH, it is inevitable that the NH will have more convective instability and the SH less. At this stage, the SH is falling faster than the NH is increasing but that will likely change as the NH oceans really get warm.
Attached is the differences for OLR and SWR by latitude from 2001 to 2023. Quite dramatic changes and most noticeable difference is just north of the Equator. This is due to expanding extent of 30C warm pools in August and September north of the Equator and the associated convective instability. Changes at these low latitudes are not going to spin up cyclones. But the warm pools are expanding north. In 2023 ocean off Japan got up to 30C.
I will be surprised if there is not an increase in NH cyclones in coming years. The warm pool extent in the NH is increasing by 2.5% of the ocean area each decade. That trend is locked in for quite a few centuries.
The other noteworthy aspect is that atmospheric water over oceans is increasing on average at 0.4mm/decade. From the Equator to 15N it is increasing at 0.8mm/decade. The extra atmospheric moisture also finds its way to land and more CAPE is developing over land. Australia is starting to look a bit like the Amazon in recent years. One tropical low this year spun up over land and persisted for more than a week.
The Mediterranean is also hitting the 30C limit and developing CAPE conducive to spinning up tropical storms. These storms will eventually transform Northern Africa.
is there any data that plots the trend in the average differential temperature from the tropics to the north and south poles?
Has this differential been increasing or decreasing with “climate change”?
The ITCZ is migrating northward at about 3km a year on land and a bit less over water.
The sea ice in Antarctica is not much changed so the drop in temperature per latitude is slightly lower in the SH.
The NH depends on the extent of sea ice in the Arctic. It is trending down probably at about the same rate the ITCZ is migrating north. So not much difference overall in the NH.
It is a bit different on a local basis. The northward currents of the western Pacific and Atlantc are taking warmer water further north. So there is greater temp/degree in certain regions. Most noticeable is Alaska. Warmer water on the southern side but still Arctic water on the Northern side. Last year in October, there was 9C across the 9 degrees latitude of Alaska.
This situation was noticeable this past winter with Alaska getting a lot of snow and particularly early season snow.
The South Pacific will have 30C at 15S in March and -1C at 60S. So 31C/ 45 degrees. Somewhat less than across Alaska.
Decreasing since 1975 as the northern half of the NH warms much faster than the southern half of the NH.
Since Arctic warming is in the six colder months of the year, the declining temperature differential mainly affects those six months. Those six months do not exactly match the traditional six month Atlantic hurricane season (June through November), but they are close.
This decline of the temperature differential since 1975 should cause fewer extreme weather events in the Northern Hemisphere. And that has happened.
Just eyeballing Figure 1, it seems like there’s a rough correlation between ENSO and hurricane count, but it’s the opposite of what you would guess. Warm ENSO seems to encourage higher total storm counts, La Niña lower counts. Is that because of the difference between how each phase manifests in the Northern and Southern Hemispheres?
It is often “opposite” because ENSO is incorrectly viewed as a key indicator of hurricane activity. ENSO is just one of many inter-related factors, including the MJO, QBO, AMO, PDO, AO, NAO, Brewer-Dobson circulation, Hadley & Walker circulations, sunspot cycles, an occasional volcano, and probably some others we don’t yet know about. This is why no one can accurately predict the next season’s hurricane activity.
Hang on, I thought the tropical hotspot was a myth. Now it isnt?
Well, aside from the warmunists’ blather about models, we actually have two rather extreme models that are actual planets in our solar system.
Venus has the hottest atmosphere of any planet in the solar system. At the surface of this rocky planet, the average atmospheric temperature is approx. 870 deg F or 465 deg C. But there is very little “weather” experienced on the surface of Venus, where winds average less than 5 km/h, a moderate walking speed, and there is very little variation of winds across the surface, and almost no diurnal variation in either temperature or wind speeds. The latter is believed to be due to the very slow rotational speed of Venus and it’s very small axial tilt compared to earth, the atmosphere and weather of which is heavily influenced by the Coriolus Effect, and by the presence of oceans of water covering 70% of the planet’s surface. The atmosphere of Venus is of course constituted mostly of carbon dioxide.
Contrast Venus to Jupiter, considered the stormiest planet in the solar system. Jupiter is a gas giant planet, not a rocky planet. Jupiter is also one of the coldest planets in the solar system, with an average atmospheric temperature of minus 234 deg F/145 deg C. Jupiter is known, of course, for its extremely stormy atmosphere, with wind speeds of up to 1,118 mph/1,800 km/hour.
So much for hot atmospheric temperatures causing storminess, and cold temperatures suppressing storminess.
Of course, there are numerous factors affecting storminess, and storminess also varies with height in the atmosphere above ground, if in fact there is ground (as on a rocky planet, vs. gas giants which have no solid surface). Planetary rotational speed, axial angle of rotation, presence of liquid water at the surface, atmospheric chemical makeup, atmospheric density, etc. etc.
The warmunists keep insisting that there is one and only one “temperature knob” for Earth, and that is CO2 concentration, and that knob also controls every other aspect of our atmosphere including storminess. They merely reveal their own ignorance of physics and chemistry.
US landfalling hurricanes have been declining since the late 1800s. Those years included natural global warming from 1910 to 1940, global cooling from 1940 to 1975 and global warming from 1975 to 2024
Thie data here started at 1980 in the first chart. That makes me suspicious
Japanese typhoons have been in a declining trend since the mid-1950s.
Meaning we have a known global decline of hurricanes for almost 70 years.
But this author seems to be interested only in the past 43 years, which is almost all of the past 48 year global warming trend.
I am rejecting this article for my blog’s daily recommended reading list because it appears to cherry pick data for the period that best supports a theory.
CAPE or Convective Available Potential Energy is the amount of fuel available to a developing thunderstorm. More specifically, it describes the instability of the atmosphere and provides an approximation of updraft strength within a thunderstorm.