Climate change may lead to more severe tropical cyclones in mid-latitude cities such as New York, Beijing and Tokyo due to rising temperatures.
Tropical cyclones are named after the fact they occur almost exclusively at low latitudes.
Key to these storms are warm sea surface temperatures of at least 81°F (27°C) and converging low-level winds that force air to rise and form storm clouds.
The planetary spin interaction with moist rising air will cause it to turn cyclically as long as it is sufficiently far from the Equator.
The jet streams limit cyclones’ range at higher latitudes, just like cyclones are not formed too near the equator.
Research by Yale University-led experts, however, suggested that global warming will reduce the temperature differential between the equator and the poles.
This, they warn, could weaken the jet stream at mid-latitudes, allowing cyclones to form — by 2100 — over a wider range than they have in the last 3 million years.
The ability for more tropical cyclones to form at mid-latitudes, where most of the world’s population lives, will place millions more within their devastating reach.
The rising temperatures could lead to more tropical storms striking mid-latitude cities, such as Tokyo and New York. Pictured: a satellite image of ‘Sam’, the strongest tropical cyclone to form in 2021’s Atlantic hurricane season
Tropical cyclones are named after the fact they occur almost exclusively at low latitudes. Pictured: Typhoon Goni batters the coast of the central Philippines’ Sorsogon province on November 1, 2020
The investigation by physicist Joshua Studholme of Yale University and colleagues was inspired in part by September 2020’s subtropical storm Alpha — the first ever cyclone to make landfall in mainland Portugal.
‘We hadn’t observed this before,’ Dr Studholme told BBC News.
“You were hit by a typical mid-latitude storm. […]Its decay created the conditions necessary for a tropical storm to form.
Portugal had not seen this before.
Their study reviewed the existing literature on the effects of climate change upon the jet streams and tropical atmospheric circulation.
They did so, however, through the lens of how these effects interact with the complex physical processes that occur on the scale of individual storms.
Studholme stated, “What we did was make clear the connections between the physical processes that go on in storms and the dynamic of the atmosphere at the planet scale.”
“This is an extremely difficult problem, because the physics of this issue isn’t well simulated in modern numerical models.
Key to the formation of tropical cyclones (aka hurricanes) are warm sea surface temperatures of at least 81°F (27°C) and converging low-level winds that force air to rise and form storm clouds. If the developing system is sufficiently far from the equator then planetary rotation will be able to interact with moist air flowing in, which causes it to spin cyclically. This is the Northern Hemisphere hurricane structure.
Pictured: Earth’s atmosphere on July 22, 2017, as captured by NASA . This day was special as it featured the largest number of simultaneous tropical cyclones in the satellite record
The team noted that simulations of Earth’s past warm climates — such as found in the Eocene (56–33.9 million years ago) and Pliocene (5.3–2.6 mya) epochs — suggest that typical cyclones can form and intensify at higher latitudes than today.
This team has confirmed a series of other studies that show climate change can increase the chance of future tropical cyclones.
In fact, the Intergovernmental Panel on Climate Change wrote in their sixth assessment report last August that they had a ‘high confidence’ that humanity’s influence on the climate was leading to a strengthening of tropical cyclones.
They concluded that ‘The global proportion of severe tropical cyclones and average peak tropical wind speeds will rise with rising global warming’.
Alongside being able to strike populated areas that were previously out of bounds, the mid-latitude tropical cyclones enabled by climate change may sport dangerous differences from their lower latitude counterparts.
‘Tropical cyclones in the mid-latitude band could experience other changes such as slower motion and heavier rainfall,’ hurricane researcher Gan Zhang — formerly of Princeton University and who was not involved in the present study — told the BBC.
He said that “These tropical cyclones, along with pronounced coastal sea-level rise, might compound potential social impacts.”
The team noted that simulations of Earth’s past warm climates — such as found in the Eocene (56–33.9 million years ago) and Pliocene (5.3–2.6 mya) epochs — suggest that typical cyclones can form and intensify at higher latitudes than today. Pictured: Tropical cyclone tracks seen in the present (top) as compared to the Eocene and the preceding Palaeocene epochs (bottom)
The team did have some good news, however — noting that tackling climate change by drastically reducing carbon emissions over the next decade could help to stop tropical cyclones from forming at mid-latitudes in the first place.
Studholme stated that the temperature gradient between the poles and the tropics is what controls this. This has a strong connection to global climate change.
“By the middle of this century, it will be clear that there is a significant difference in how high-emission scenarios compare to low emission ones.
“It can have a significant impact on how the hurricanes will play out.”
Nature Geoscience has published all of the findings.
WHAT IS IN A NAME CYCLONES VS. HURRICANES, VS. TYPHOONS
Photo: Flooding in Houston, Texas in 2017 after Hurricane Harvey. Because of the location on Earth where it happened, the tropical cyclone is called a hurricane.
The meteorologists call them a “Tropical Cyclone”, which is the generic term for the rotating storm system that can also be called hurricanes, storms, cyclonic thunderstorms or tropical depressions.
Hurricane is the specific name for these phenomenon when they are located over the Atlantic or north east Pacific oceans.
The designation of typhoon, meanwhile, refers to those that occur over the north-western Pacific, south Pacific, Indian Ocean and — very rarely — above the South Atlantic.
Regardless of the name used, all feature a rapidly rotating storm system characterised by strong winds, a spiral arrangement of thunderstorms that produce both heavy rain and sudden squalls, all of which circulate around a low-pressure centre — sometimes called the ‘eye’ of the storm.