SUPER cyclone Amphan has recently left trails of devastation in the south-west of Bangladesh and in parts of the neighbouring in Indian state of West Bengal. The death toll, according to EcoWatch (May 22, 2020), was at least 84.
The UN’s office in Bangladesh estimated that 10 million people were affected and 500,000 people may have lost their homes. Media reports said: Millions of people in Bangladesh and India were evacuated to cyclone shelters before the cyclone hit. The storm, according to the Guardian (May 21, 2020), ‘smashed windows, pulled down trees and pylons and overturned cars’ in Kolkata.
The cyclone that devastated parts of the southwestern Bangladesh and the Indian city of Kolkata was born in the Bay of Bengal, a place of birth of majority of the deadliest storms. According to Weather Underground (May 15, 2020), 26 of the 35 ‘deadliest tropical cyclones in world history have been Bay of Bengal storms’. ‘[T]he frequency of intense cyclones has risen in the Bay of Bengal in recent decades.’ (BBC, May 19, 2020)
Cyclone Nargis, the report referred, hit the Irrawaddy Delta in Myanmar in May 2008 with the death toll reaching at least 140,000. Its impact displaced two million people. The last super cyclone to hit the region was in 1999 and the Indian state of Odisha received the hit, which took toll with about 10,000 deaths. (ibid)
Western Australia battened down for its worst storm in 10 years on May 24, 2020. Remnants of a tropical cyclone met a cold front with heavy rains and storm surges. Peak wave heights were, it was warned, to reach seven to 10 meters. Homes were destroyed and tens of thousands of people were without power as a ‘once in a decade’ storm that pummelled the western half of Western Australia on May 24, 2020.
In the United States, tropical storm Arthur brushed the North Carolina coast in May. In 2019, Hurricane Dorian, a monster Category 5 storm, devastated the Bahamas. The Union of Concerned Scientists said: ‘Cutting edge research is beginning to be able to attribute individual hurricanes to global warming.’ (July 16, 2008; updated June 25, 2019) And, cyclone season in the United States, officially the hurricane season is June 1–November 30, is going to begin within days. In Bangladesh, cyclones are regular incidents threatening life and livelihood.
Climate change sparks stronger hurricanes
A NEW study (James P Kossin, Kenneth R. Knapp, Timothy L. Olander, and Christopher S Velden, ‘Global increase in major tropical cyclone exceedance probability over the past four decades’, Proceedings of the National Academy of Sciences, May 18, 2020) by scientists at the US National Oceanic and Atmospheric Administration and the University of Wisconsin at Madison has found climate change is making hurricanes more powerful than these were four decades ago. The risk of hurricanes/cyclones/typhoons reaching Category 3 or higher has been increasing 8 per cent per decade, which means these are turning larger and more intense.
James P Kossin, a NOAA scientist and the lead author of the study report, explained to CNN (May 18, 2020) the ‘8 per cent increase per decade’: ‘[D]uring its lifetime, a hurricane is 8% more likely to be a major hurricane in this decade compared to the last decade.’
And, category-3 storms, according to the Saffir-Simpson Hurricane Wind Scale, create ‘Devastating damage […]: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.’ (NOAA, National Hurricane Centre and Central Pacific Hurricane Centre)
The study found: in almost every region of the world where hurricanes form, their maximum sustained winds are getting stronger.
‘Our results show that these storms have become stronger on global and regional levels, which is consistent with expectations of how hurricanes respond to a warming world’, Kossin said in a statement. (W News, University of Wisconsin-Madison, May 18, 2020)
The focus of the study was the identification of global changes in tropical cyclone intensity. The TCs are referred to by different names in different regions, eg, hurricanes in the North Atlantic and typhoons in the western North Pacific. But, for simplicity, the scientists conducting the study have referred to any Saffir-Simpson category 1 or greater intensity as ‘hurricane’ intensity, and Saffir-Simpson category 3 or greater intensity as ‘major hurricane’ intensity regardless of geographic region.
The significance of the study, as the study report says, is: ‘The TCs, and particularly major TCs, pose substantial risk to many regions around the world. Identifying changes in this risk and determining causal factors for the changes is a critical element for taking steps toward adaptation. Theory and numerical models consistently link increasing TC intensity to a warming world, but confidence in this link is compromised by difficulties in detecting significant intensity trends in observations. The study identifies significant global trends in TC intensity over the past four decades.’
The results, says the report, should serve to increase confidence in projections of increased TC intensity under continued warming.
The study analysed 40 years of satellite images including infrared temperature measurements to estimate hurricane intensity.
Theoretical understanding of the thermodynamic controls on the TC wind intensity, and numerical simulations implies a positive trend in TC intensity in a warming world, says the report.
However, the report says, the global instrumental record of TC intensity is known to be heterogeneous in both space and time and is generally unsuitable for global trend analysis. To address this, a homogenised data record based on satellite data was previously created for the period 1982–2009. The 28-year homogenized record exhibited increasing global TC intensity trends, but they were not statistically significant at the 95 per cent confidence level. Based on observed trends in the thermodynamic mean state of the tropical environment during this period, it was argued that the 28-year period was likely close to, but shorter than, the time required for a statistically significant positive global TC intensity trend to appear.
The study, therefore, extended the homogenised global TC intensity record to the 39-year period 1979–2017, and statistically significant (at the 95 per cent confidence level) increases were identified. Increases and trends were found in the exceedance probability and proportion of major (Saffir-Simpson category 3 to 5) TC intensities, which is consistent with expectations based on theoretical understanding and trends identified in numerical simulations in warming scenarios. Major TCs pose, by far, the greatest threat to lives and property. Between the early and latter halves of the time-period, the major TC exceedance probability increases by about 8% per decade.
Potential intensity has been increasing, in general, as global mean surface temperatures have increased, and there is an assumption that the distribution of TC intensity responds by shifting toward greater intensity.
The study results say: ‘Over the past 40-y (and longer), anthropogenic warming has increased sea surface temperature (SST) in TC-prone regions, and, in combination with changes in atmospheric conditions, this has increased TC potential intensity in these regions. An increase in environmental potential intensity is expected to manifest as a shift in the TC intensity distribution toward greater intensity and an increase in mean intensity. More importantly, the shift is further expected to manifest as a more substantial increase in the high tail of the distribution, which comprises the range of intensities that are responsible for the great majority of TC-related damage and mortality. Consequently, detection and attribution of past and projected TC intensity changes has often focused on metrics that emphasize changes in the stronger TCs.
‘The greatest changes are found in the North Atlantic, where the probability of major hurricane exceedance increases by 49% per decade. Large and significant increases are also found in the southern Indian Ocean. More modest increases are found in the eastern North Pacific and South Pacific, and there is essentially no change found in the western North Pacific. The northern Indian Ocean exhibits a decreasing trend, but it is highly insignificant and based on a small sample of data. With the exception of the northern Indian Ocean, all of the basins are contributing to the increasing global trend.’
The new study finding is the latest evidence that capitalism-induced global warming is creating cyclones with deadly force and frequency which take heavy toll on life and economy.
Farooque Chowdhury writes from Dhaka.
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