Climate change supercharging extreme events, scientists say, as 'super cyclone' Amphan hits Bangladesh and India
BANGKOK: As a powerful “super cyclone” tore into the coastline of the Bay of Bengal on Wednesday (May 20), leading experts warned of the impacts climate change was having on supercharging extreme weather events.
Cyclone Amphan brought with it severe winds, very heavy rainfall and the risk of damaging storm surges as it made landfall over India’s West Bengal and Bangladesh, a region with a dense and highly vulnerable population.
It was only the second “super cyclone” to have been recorded in the north-eastern Indian ocean and the most powerful since the 1999 Odisha storm.
More than three million people are at risk, with authorities warning that Amphan presented a more serious threat than the coronavirus pandemic.
Tropical cyclones get their energy from warmer temperatures and the preceding weeks have provided the perfect conditions for this powerful and fast forming storm system, climate scientists say.
They observed sustained, abnormally high sea surface temperatures of 32 to 34 degrees in the Bay of Bengal throughout May. In less than a day, Cyclone Amphan formed and morphed into a monster.
“There was a rapid intensification from a category one cyclone to a category five cyclone, in a very short time span - 18 hours - which is unprecedented. It’s one of the strongest cyclones the Bay of Bengal has ever seen,” said Dr Roxy Mathew Koll, a scientist with the Indian Institute of Tropical Meteorology and lead author of the United Nations' Intergovernmental Panel on Climate Change (IPCC) special report on oceans and cryosphere.
“From the data, we feel that ocean temperature is a major component in this intensification. We saw that the temperatures were very much high before the cyclone formation,” he said.
The fast development of Cyclone Amphan gave authorities only a short window to prepare. Millions of people were forced to evacuate and emergency and aid services were on standby for Amphan’s arrival, in a period when both India and Bangladesh are in a form of lockdown due to the global COVID-19 pandemic. It further complicated an already logistically problematic evacuation effort.
“We are particularly concerned about communities in low-lying areas, many of whom stand to lose their livelihoods. Mass evacuations have been taking place in recent hours and days, however, this is made all the more difficult by COVID-19 and efforts to enforce social distancing,” Bidisha Pillai, the CEO of Save the Children in India, said in a statement.
Cyclones are fairly common in this part of the world. In 2007, Cyclone Sidr wreaked havoc in Bangladesh, killing about 3,500 people. Further back, more than 138,000 people died in a 1991 cyclone and storm surge disaster.
Yet as global temperatures increase due to climate change, so too does the risk of more regular powerful super cyclones like Amphan, according to Prof Mark Howden, IPCC vice-chair and director of The Climate Institute at the Australian National University.
“It’s becoming increasingly key that climate is a key driver, even if we can’t say for any given cyclone that this is caused by climate change,” he told CNA.
“What is clear is that climate change, which is driving high sea surface temperatures, is resulting in a tendency towards higher cyclone strength. We’re seeing more category 3, 4 and 5 cyclones, in both absolute numbers and in the proportion of cyclones.
“Any category 4 or 5 cyclone is a real potentially life threatening event. When you see them developing so quickly it tells you something about the energy they’re drawing from, and that energy is connected to climate. It’s terrifying,” he added.
In the Bay of Bengal - and many other parts of the world - there is a compounding effect of “multiple extremes” interacting at the same time with each other, all fuelled by climate change, Dr Koll explained.
“For example you have increasing sea levels in the background and then have you high tides and along with that heavy rains and storm surges due to tropical cyclones. When you have these multiple elements working together, the impact is high,” he said.
A new report released this month by the American Meteorological Society reinforced views that extreme rain events in monsoonal areas were becoming more frequent due to global warming and were likely to aggravate flooding in coastal areas when combined with other factors, like cyclones and sea level rise.
“All around the Indian Ocean, these are mostly low lying lands with high populations vulnerable to these extreme events. Only a few of them have early warning systems or the means to adapt or mitigate climate change, so when these extreme events happen together it can seem hopeless,” Dr Koll said.
Some scientists have also suggested that the lack of air pollution, an otherwise welcome outcome in a typically heavily polluted region, could have added to this cyclone’s intensity.
Aerosols, tiny particles that are the product of pollution, provide a cooling effect and can help boost cloud formation and reduce solar radiation, which heats up the surfaces of the ground and sea.
The Bay of Bengal recorded clear skies and a lack of wind, in addition to high surface temperatures, before the formation of Cyclone Amphan. At the same time, India has recorded record low levels of emissions in recent weeks.
As Prof Howden explained, aerosols can impact how a cyclone behaves. “Aerosols tend to reduce the strength of cyclones and wind speed and also reduce their duration. They do that by generating rainfall - instead of at the centre of a cyclone - further out at the edges of the cyclone,” he said.
But there are complex forces at play in the atmosphere. While climate change impacts are clearer, more studies need to be done to connect air pollution and the intensity of this cyclone.
“This might just be a factor of whether there’s clouds or not. Whether there were less clouds because there are less aerosols or air pollutants over the ocean, we don’t know how much direct impact there is," Dr Koll said. "I don’t see a direct connection just yet.”