Study reconstructs old storms to help predict changes in tropical cyclone hotspot
WOODEN HOLE, Mass., November 16, 2020 / PRNewswire / – Intense tropical cyclones are expected to become more frequent as climate change increases temperatures in the Pacific Ocean. But not all regions will experience storms of the same magnitude. New search of the Woods Hole Oceanographic Institution (WHOI) published in Geosciences of nature reveals that tropical cyclones were in fact more frequent in the south Marshall Islands during the Little Ice Age, when temperatures in the northern hemisphere were colder than they are today.
This means that changes in atmospheric circulation, driven by differential warming of the oceans, strongly influence the location and intensity of tropical cyclones.
In the first such study so close to the equator, the lead author Jacques Bramante reconstructed 3,000 years of storm history on Jaluit atoll in the south Marshall Islands. This region is the cradle of tropical cyclones in the western North Pacific, the most active tropical cyclone zone in the world. Using differences in sediment size as evidence of extreme weather events, Bramante found that tropical cyclones occurred in the region about once per century, but increased to a maximum of four per century from 1350 to 1700 CE. era, a period known as the Little Ice Age.
Bramante, young graduate of the Joint MIT-WHOI Program in Oceanography / Applied Ocean Science and Engineering, claims that this finding sheds light on how climate change affects where cyclones can form.
“Changes in atmospheric circulation due to modern human-induced global warming are the opposite of changes in circulation due to the Little Ice Age,” notes Bramante. “So we can expect to see the opposite effect in the deep tropics – a decrease in tropical cyclones near the equator. This could be good news for the south. Marshall Islands, but other areas would be threatened as the average location of the cyclone generation moves north, ”he adds.
During major storms, coarse sediments are stirred up and deposited by currents and waves in “blue holes“, ancient caves that collapsed and turned into sinkholes that filled with seawater for thousands of years. In a 2015 field study, Bramante and his colleagues took samples of a blue hole on Jaluit Atoll and found coarse sediment among the finest grains of sand. After sorting the grains by size and analyzing data from Typhoon Ophelia, which devastated the atoll in 1958, the researchers had a model to identify other thunderstorm events appearing in the sediment record. They then used radiocarbon dating – a method of determining the age by the ratio of carbon isotopes in a sample – to date them. sediment in each layer.
Armed with data previously collected on the ancient climate from tree rings, coral coral and fossilized marine organisms, the researchers were able to reconstruct the conditions that existed at the time. By linking this information to the recording of storms stored in the sediments of Jaluit Atoll, the researchers demonstrated by computer modeling that the particular set of conditions responsible for the equatorial trade winds had a strong influence on the number, intensity and size. location where cyclones would form.
Jeff donnelly, a senior scientist from OMSI and co-author of the study, used similar methods to piece together the history of hurricanes in the North Atlantic and Caribbean. He plans to expand the Marshall Islands study west to The Philippines study where tropical cyclones have historically formed and how climatic conditions influence the path and intensity of a storm. A better understanding of storm behavior under previous conditions will help scientists understand the causes of changes in tropical cyclone activity and help people living in coastal communities prepare for extreme weather conditions in the future, a- he declared.
“With the geological record, we can get a baseline that tells us how much of a risk we really are in a given location,” Donnelly said. “It turns out that the past provides useful analogies for the climate change we are currently experiencing. Earth has already done this experiment. Now we are trying to go back and determine the drivers of tropical cyclones.”
Additional co-authors of this study include geologist WHOI Andrew Ashton; WHOI physical oceanographer Caroline Ummenhofer; Murray Ford (University of Auckland, New Zealand); Paul Kench (Simon Fraser University, British Columbia, Canada); Michel Toomey (US Geological Survey, Reston, Virginia); Richard sullivan of Texas A&M University; and Kristopher karnauskas (University of Colorado, Boulder).
Key points to remember
The researchers reconstructed the history of tropical cyclones in the south Marshall Islands over the past 3000 years. The western North Pacific is the most active area for tropical cyclones, but has been under-studied compared to the North Atlantic.
During the Little Ice Age, tropical cyclones formed in the deep tropics of the Pacific Northwest more often than at any other time in the record. The sediment sample data recorded four tropical cyclones per century, which is well above the average of 3,000 years of one per century.
Climate change should create conditions opposite to the Little Ice Age, indicating that tropical cyclones will form less often in the south Marshall Islands, even if storms are expected more frequent and intense at higher latitudes.
This research was funded by the Strategic Environmental Research & Development Program, a partnership between the Department of Defense, the Department of Energy and the Environmental Protection Agency.
The Woods Hole Oceanographic Institution (WHOI) is a private, non-profit organization Cape Cod, Massachusetts, dedicated to marine research, engineering and higher education. Founded in 1930, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate an understanding of the role of the ocean in the changing global environment. WHOI’s pioneering discoveries stem from an ideal combination of science and engineering, which has made it one of the most reliable and technically advanced leaders in fundamental and applied ocean research and exploration. WHOI is known for its multidisciplinary approach, superior naval operations and unparalleled deep-sea robotics capabilities. We play a leading role in ocean observation and operate the world’s most comprehensive suite of data collection platforms . Top scientists, engineers and students collaborate on more than 800 simultaneous projects around the world, both above and below the waves, pushing the boundaries of knowledge and possibility. For more information, please visit www.whoi.edu
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SOURCE Woods Hole Institute of Oceanography