Chinese-led research is challenging the idea of a direct link between warmer temperatures and more extreme typhoons, with a new study suggesting that bigger and deadlier tropical storms occurred in the past when temperatures fell.
An international team led by Chinese Academy of Sciences researcher Chen Tianran found that over the past few hundred years, the frequency and intensity of typhoons in the South China Sea increased at times when global temperatures dropped.
The pattern was uncovered in sediment and historical records from China’s southern coastal province of Guangdong, according to their paper, published in the journal Geophysical Research Letters last month.
Between 1600 and 1900, world temperatures dropped by 1 to 1.5 degrees Celsius (1.8 to 2.7 Fahrenheit) – a period known as the Little Ice Age.
Before that, about three or four typhoon landfalls were recorded each year in Guangdong. By the middle of the 17th century, the number had peaked at around 12.
The researchers also analysed a sediment sample drilled from a sand pit on Guangjin Island, near the Yongle Atoll in the disputed Paracel Islands, which China calls the Xisha Islands.
Chen’s team and researchers from the University of Queensland in Australia sieved and counted grains of sediment. They proposed that the higher the proportion of larger particles in a given period, the bigger and more frequent the storms were in that time, because stronger wind could carry larger grains.
They determined the age of the sediment by testing uranium and thorium elements in fragments of coral, and found that their sediment records tallied almost perfectly with the numbers of typhoons logged by Chinese government officials in coastal areas.
Huang Fei, professor of atmospheric science with the Ocean University of China in Qingdao, said the discovery was not entirely a surprise.
“Cooling can increase the ice cap and widen the temperature gap between the polar region and equator – which in theory can boost tropical storm activities,” Huang, who was not involved in the study, said.
“I don’t think these results are in conflict [with other forecasts of global warming increasing the risk of extreme weather].
“Rising temperatures can weaken the westerly [a belt of prevailing westerly winds in the northern hemisphere that acts as a constraint on the Arctic wind]. Chilling winds would therefore venture further south in winter and trigger stronger responses in the tropical atmosphere.”
Huang added that more than one such phenomenon determined the storm patterns.
Some studies, including one by a separate team of Chinese scientists published by journal Scientific Reports in 2014, have suggested the present warm phase could end over the next few decades, ushering in a 250-year cool phase.
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This article Why global warming may not mean more typhoons, according to new study first appeared on South China Morning Post