Cyclone Amphan: Exploring links with climate change
Waves crashing into the Patenga Beach in Chattogram on Tuesday, May 19, 2020, as the country braces for cyclone Amphan.
Cyclone Amphan -- a storm promising to break many an old record -- is expected to make landfall in India and Bangladesh on May 20 late in the afternoon.
Amphan is now the strongest storm on record in the Bay of Bengal, with sustained wind speeds of 270kmh, making it even stronger than the 1999 super cyclone.
Experts and multiple studies have said that climate change is increasing the damage that cyclones cause.
As this storm comes amid the Covid-19 pandemic, serious repercussions are expected for Bangladesh.
"Cyclone Amphan, which is about to hit Bangladesh, is going to compound the Covid-19 pandemic as well as lockdown and social distancing measures," opined Dr Saleemul Huq, Director of the International Centre for Climate Change and Development, Independent University Bangladesh.
"While Bangladesh has an enviable system of cyclone warning and cyclone shelters, it will be almost impossible to practice social distancing in those shelters," he added.
A NEW WORLD OF SUPER CYCLONES
Bangladesh has been subject to cyclones for years now but stronger cyclones have become more common across the world and scientists project that climate change will continue to make them even more powerful.
The strength of cyclones affecting the countries bordering the Indian Ocean has been increasing as the planet has warmed, according to multiple studies.
Cyclones are also fueled by heat. Warming seas can make cyclones more powerful by increasing the potential energy available to them, effectively increasing their power ceiling or speed limit.
The potential storm surge from Amphan may be among the most dangerous threats from the storm. Increases in storm surge related to climate change can be due to rising sea levels, increasing size, and increasing storm wind speeds.
India and Bangladesh could experience dramatic annual coastal flooding by 2050, affecting 36 million people in India and 42 million in Bangladesh, according to a major 2019 study in the journal Nature.
A growing proportion of tropical cyclones are developing quickly, known as rapid intensification, according to multiple studies -- these changes are linked with climate change. This is a threat because it makes it harder to forecast how a storm will behave and thus prepare before it makes landfall.
"Our research shows that high ocean temperatures are conducive for rapid intensification of cyclones in the north Indian Ocean," said Dr Roxy Mathew Koll, Scientist, Indian Institute of Tropical Meteorology, Lead Author, IPCC Oceans and Cryosphere.
"In the current case, Bay of Bengal has been particularly warm, which may have had some role in the rapid intensification from a depression to a cyclone and then to a super cyclone in a very short time. For example, some of the buoys in the Bay of Bengal registered maximum surface temperatures of 32-34°C consecutively for the first two weeks of May," Dr Roxy further said.
The scientist also said, "These are record temperatures driven by climate change -- we have never seen such high values until now. These high temperatures can super charge a cyclone since tropical cyclones primarily draw their energy from evaporation at the ocean surface. The high sea surface temperatures were recorded by the INCOIS/NIOT moored buoys in the Bay of Bengal. The temperatures drop once the depression or cyclone is formed."
LOCKDOWNS AMPLIFYING CYCLONE STRENGTH?
There is a complex relationship between air pollution and cyclones, and it is possible that reductions in air pollution in the region, due to the Covid-19 restrictions, may have influenced Cyclone Amphan.
Aerosols, from human-caused air pollution, can partly reduce the strength of cyclones in various ways. One factor is that aerosols reduce the amount of sunlight reaching the Earth's surface, cooling it slightly. Reductions in air pollution may have slightly increased sea surface temperatures in the Bay of Bengal, adding to the effect of climate change.
But another factor that influences cyclone strength, wind shear, has the opposite relationship with air pollution. Higher air pollution tends to reduce wind shear, which generally allows stronger cyclones to form. So reduced air pollution could, in this respect, limit cyclone strength.
So, while there may be a relationship between the reduction in air pollution, due to the Covid-19 restrictions, and Cyclone Amphan, it is too soon to say exactly what influence cleaner air has had on the storm.
"Global warming is leading to an increase in the heat content of the upper oceans around the globe. This is also true for the oceanic regions around the Indian region. This is one of the causes of the increasing number of cyclonic activities in our region during pre-monsoon times," said Dr V Vinoj, assistant professor, School of Earth, Ocean and Climate Sciences, Indian Institute of Technology, Bhubaneswar.
"However, what is different now than the past is the world's largest Covid-19 lock-down in the South Asian region led by India. This lockdown has significantly reduced human emissions into the atmosphere. This decrease means that surface warming due to the removal of human-made aerosols has increased and atmospheric warming has decreased significantly during this time. This surface warming extends over the waters in the Bay of Bengal. Therefore, the global warming effect which tends to increase the strength of cyclones, if any, is now amplified due to this human-induced lockdown effect. This may be the reason why Amphan has strengthened into a super cyclone, a second one only to the 1999 super cyclone," Dr V Vinoj added.
"Overall, I feel lockdown may have strengthened this cyclone due to the additional warming of the ocean waters over the Bay of Bengal. This will need to be investigated in the future."