Ongoing heatwave - is it the impact of El Niño?
18 April 2023
Dr Matiur Rahman :
The country is burning in the intense heat of April. The intense heat wave is flowing over eight districts, including Dhaka. The weather department said that this situation might continue. A fierce heat wave is sweeping Dhaka, Faridpur, Manikganj, Pabna, Bagerhat, Jessore, Chuadanga and Kushtia districts. A mild to moderate heat wave is sweeping other parts of the country. This situation may continue.
On April 14, 2024, Dhaka's temperature rose to 40.2 degrees Celsius. Before that, in 1965, the temperature of Dhaka rose to 42 degrees Celsius. And the highest temperature in the history of Dhaka was recorded in 1960. The mercury rose to 42.2 degrees Celsius.
Over the last few years, extreme heat during summer and intense rainfalls during rains have been increasingly challenging human civilization. But why is this climate hostility? Experts say that along with global warming, these natural disasters are occurring under the influence of El Nino and La Nina.
The climate of the Pacific region goes through a cycle of three phases. This cycle is called the Enso cycle. Three stages of the Enso cycle: El Niño and La Niña; when these two are not dominant, it is called Enso neutral.
El Nino is the dry season with less rain than usual and less flooding. During this time, the temperature rises excessively. And during La Niña, there is more rain and more flooding. The temperature drops below normal.
El Nino means boy in Spanish, and La Nina means girl. But these two words are known to be serious environmental polluters. Their definition depends on the temperature of the central and eastern Pacific regions. A temperature limit is set here. The long-term average temperature is 3 to 5 degrees Celsius. When it goes down, it is called La Nina; when it goes up, it is called El Nino.
However, if this rise or fall in temperature lasts more than five months, it is called an El Niño or La Niña episode. Usually, this condition lasts from 9 months to 12 months. Sometimes it can last up to 3 years. This cycle may return every two to seven years.
Many scientists refer to El Nino as the heartbeat of the earth. The ocean and adjacent atmosphere suddenly warm up a few months in the eastern Pacific every few years. This results in massive changes in the global climate. Scientists call these cyclic ups and downs of the atmosphere the earth's heartbeat.
Although El Niño indicates drought or no rain, experts say its effects generally increase surface pressure along the Indian Ocean, Indonesia and Australia. Air pressure decreases over Tahiti and the eastern and central Pacific. The South Pacific trade winds weaken or begin to blow eastward. As warm air condenses near Peru, precipitation begins in the northern desert region of Peru. Warm water from the Indian and Western oceans spreads into the Eastern Pacific. It carries with it a large amount of water vapour, i.e. rain. As a result, the western Pacific region burns with drought, while the eastern Pacific receives abundant rainfall.
According to climate scientists, the effects of La Nina increase the severity of winters in the eastern Pacific Ocean. The threat of tropical cyclones grows. Precipitation increases in the southern and eastern parts of the Pacific Northwest. Precipitation increases in parts of North America. Winters in Canada become more severe, and snowfall increases. In mid-1987, temperatures in the central Pacific Ocean dropped 20 degrees Celsius below normal.
The causes of El Nino are still being researched. El Niño events begin when the trade winds are interrupted for many months as part of the Walker circulation process. Many Kelvin waves combine to create relatively warm water several centimetres high and hundreds of kilometres wide, making a warm sink near North America.
El Nino years typically experience below-normal rainfall in the greater Ganges-Meghna-Brahmaputra basin; Drought situation prevails. As happened in Bangladesh in 1982-83 and 1997. However, in Bangladesh this year, the rainfall was not as much as it should have been; it was somewhat droughty. For El Nino, the monsoon winds did not move as fast as they were supposed to from east to west. Rainfall has also decreased due to weak monsoon winds.
During El Niño years, storms increase in intensity. Scientists have warned that the return of the El Niño climate phenomenon later this year will cause global temperatures to rise "off the charts" and deliver unprecedented heat waves.
Early forecasts suggest that El Niño will return after 2023, fueling more extreme weather around the world and that it is "very likely" that global warming will exceed 1.5 degrees Celsius. The hottest year, 2016, was recorded by a major El Niño driven.
This year is already predicted to be warmer than 2022, which global datasets rank as the fifth or sixth warmest year on record. But El Niño occurs in the Northern Hemisphere winter and takes months to feel its warming effects, meaning a new global temperature record will likely be set in 2024.
Greenhouse gases emitted by human activities have increased the average global temperature by about 1.2C. It has already led to catastrophic effects worldwide, from heat waves to flooding, cyclone and fires in many parts of the globe. Under climate change, the impact of El Niño events will be stronger, and we're likely to see unprecedented heat waves during the El Niño.
(The writer is a researcher and
development worker).
