Global warming could be impacting tropical cyclones by shifting distribution patterns, says study
'This work provides a piece of strong evidence that the anthropogenic forcing has likely been generating a considerable impact on global tropical cyclone statistics'
A new study of four decades of data has found that global warming has resulted in shifting patterns in the distribution of tropical cyclones. The number of tropical cyclones originating in the North Atlantic and Central Pacific has slightly increased, while fewer have occurred in the Southern Indian Ocean and Western North Pacific
The study was conducted by researchers at the Geophysical Fluid Dynamics Laboratory, part of the National Oceanic and Atmospheric Administration in Princeton. Other factors, such as large volcanic eruptions and the human-driven release of aerosols, have also played a role in altering the global distribution of cyclones.
Storms that develop in the tropical oceans at least 5-30 degrees latitude north or south of the equator are called tropical cyclones. In these areas, sea temperatures are at least 27 degrees Celsius.
Strong tropical storms in the North Atlantic and the central and North Pacific are called hurricanes while those in the northwest Pacific are called typhoons and those in the South Pacific and the Indian Ocean are simply called tropical cyclones.
Researchers studied reliable observed tropical cyclone intensity data at the global scale — this data has only been available since 1980 — to quantify changes in tropical cyclone activity and high-resolution dynamical models to deduce the causes of change.
The study's climate models also projected decreasing trends in the number of tropical cyclones in the North Atlantic toward the end of the 21st century because of the dominant effect of increases in carbon dioxide concentrations, assuming no volcanic eruptions.
Researchers also noted that human-driven climate change is the most likely driver of increases in cyclones in the central Pacific Ocean, which surrounds Japan and the Marshall Islands.
However, it is important to note that there is currently no consensus on whether climate change is driving an increase in the global number of tropical cyclones. The world currently experiences almost 100 tropical cyclones a year.
The current study period does not include 2019 – a record year for cyclones in the Indian Ocean, told Professor Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research (NCAR) in Colorado, who was not involved with the research to Carbon Brief.
He said, "In 2019, there were four spectacular cyclones in the Indian Ocean and two of these, in the southern Indian Ocean, were unprecedented – belying the decrease found here. The 2018-19 South-West Indian Ocean cyclone season was the costliest and the most active season ever recorded since reliable records began in 1967."
Dr Hiroyuki Murakami also spoke to Carbon Brief regarding the study in which he was involved, saying, "Greenhouse gases are warming the upper atmosphere and the ocean [in these regions]. This combines to create a more stable atmosphere, with less chance that convection of air currents will help spawn and build up tropical cyclones."
Dr Murakami also said, "We don’t find any clear trend in the number of global tropical cyclones over the last 40 years. This is because there are regions showing increases or decreases. They are all canceled out, leading to no change in the total number."
Dr Shuai Wang, an atmospheric physicist from Imperial College London, who was not involved in the study told Carbon Brief, "As stated by the authors themselves, there is still uncertainty that we should bear in mind when digesting the information of this paper. Nevertheless, this work provides a piece of strong evidence that the anthropogenic forcing has likely been generating a considerable impact on global tropical cyclone statistics."