SINGAPORE — We have become acutely aware of the financial storm threatening to sweep the world. But what about nature’s most powerful storms? Will global warming cause more frequent and intense tropical cyclones, increasing the already heavy annual toll of death, damage and injury in densely populated coastal Asia?
A panel of scientists advising member states of the United Nations on climate change told policymakers late last year that it was likely future tropical cyclones “will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical sea-surface temperatures.”
The latest scientific research on cyclones, published last month, suggested that global warming has already made storms more destructive. However, the study by three U.S. weather researchers made no reference human causes for rising sea temperatures, such as the release of carbon dioxide and other greenhouse gas emissions into the atmosphere — mainly from burning coal, oil and natural gas, and clearing tropical forests. Much of this activity is happening in Asia.
The weather researchers examined photographs and other data from a single set of satellites from 1981 to 2006, a period in which sea surface temperatures rose to 28.44 C from 28.22 C. They concluded that the highest wind speeds of the most violent storms averaged 251 kph in 2006, up from 225 kph in 1981. The increases in cyclone intensity were most marked in the Atlantic and Indian Oceans, but less evident in the North Pacific, where most tropical cyclones occur. The study also found that more common and less powerful cyclones — about two-thirds of all the storms — had not become stronger in the 26 years to 2006.
An average of 90 cyclones form around the world each year. Around 50 of the most powerful reach wind strengths of 118 kph (74 mph) and above. In the North Pacific, they are known as typhoons; in the Atlantic, as hurricanes. Typhoons regularly strike Taiwan, Hong Kong, China, the Philippines and Japan in the storm season from late June until December, gathering strength in the Pacific Ocean or the South China Sea before weakening over land.
Although the Bay of Bengal has been the scene of some of the world’s deadliest cyclones, most of them have struck Bangladesh and India, not Myanmar. However, Cyclone Nargis, which hit Myanmar last May, appears to be the first high-strength storm recorded in the populous Irrawaddy River Delta in Burma, and this has prompted speculation that these cyclones may be extending their reach and striking in new places.
Shortly before the catastrophic Hurricane Katrina struck the Bahamas, Florida and Louisiana in 2005, causing nearly $100 billion in damage, Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology, attracted worldwide attention when he published a study showing hurricanes had become significantly more violent due in part to global warming. His latest research, which came out last April, confirmed that there had been a big rise in hurricane power in the last 25 years but cast doubt on whether this trend would continue in the future as the world got warmer.
Some scientists have linked stronger storms to rising sea surface temperatures in the Atlantic and elsewhere. They propound the so-called heat engine theory: because tropical cyclones draw energy from warm water and warm moist air, the warmer the water and the atmospheric temperature, the more intense the storm.
However, the three U.S. weather researchers previously mentioned found that cyclones are also affected by factors not related to ocean temperatures and that these can prevent some storms from gathering devastating strength. The shaping factors include where cyclones originate, how close they are to land, solar activity, El Nino and La Nina ocean-atmosphere cycles, as well as the speed, direction and height of wind shear.
The trouble is that even when these factors are considered disadvantageous statistically to storm development, some storms are able to emerge as banshees of destruction.
Michael Richardson is a visiting senior research fellow at the Institute of Southeast Asian Studies in Singapore.