Its potentially disastrous repercussions in the long term are well documented but some countries are already starting to face the ominous headwinds.
Bangladesh ranks among these vulnerable countries, where the temperature has been rising exponentially since the 1960s. The phenomenon has also been closely linked to an increase in infectious disease outbreaks by researchers.
In the last six decades, the average temperature has risen by 0.7-1 degree Celsius in Bangladesh. It may rise by 1.4 degrees Celsius in the next three decades, experts warn.
A look at the annual mercury readings from 1960 to 2020 shows a marked upturn in the average highest temperature, as well as the lowest temperature, said Dr Abdul Mannan, senior meteorologist of Bangladesh Meteorological Department. “On average, the region has faced an increase of 0.7 to 1 degree Celsius in temperature.”
AVERAGE HIGHEST TEMPERATURE IN PAST DECADES
Average Highest Temperature
30.3 degrees Celsius
30.1 degrees Celsius
30.2 degrees Celsius
30.1 degrees Celsius
30.4 degrees Celsius
31.2 degrees Celsius
31.1 degrees Celsius
Dr Mannan said he noticed an upward trend in the highest and lowest temperature from May 2020 to October 2021. He attributed the jump in temperature to the frequent heatwaves and other natural disasters befalling the country.
“After 2015, the rate of temperature rise was greater than usual. Sometimes, the mercury rose up to 3 degrees Celsius in the last one and a half years.”
Global warming has affected the climate in Bangladesh and the region of South Asia. Over the past 44 years, Bangladesh experienced a 0.5°C temperature increase, the World Bank said in its Climate Afflictions report.
“The summers are getting hotter and longer, winters are warmer, and the monsoon seasons are being extended from February to October. With these patterns, the country’s distinct seasonal variations are becoming blurred. By 2050, the temperatures are predicted to rise by 1.4°C in Bangladesh,” the report said.
The urban areas, especially the metropolitan areas, are experiencing hotter weather than the rural parts of the country.
Heatwaves have been quite prominent and have swept over the capital with greater frequency in recent years, experts said.
During these hot spells, the mercury hovers between 29 degrees Celsius and 34.5 degrees Celsius on average in Dhaka’s 'heat islands' -- the urbanised neighbourhoods that experience higher temperatures than their outlying areas.
A heatwave typically occurs when a vast area experiences a high temperature for three consecutive days.
A temperature between 36-38 degrees Celsius signifies a mild heatwave, 38-40 degrees Celsius a moderate heatwave, while the level above 40 degrees Celsius is considered an extreme heatwave.
“There's a rising trend of heat waves sweeping over the country, mostly in July. The time and range are changing [for these natural phenomena],” Dr Mannan said.
"For the last few years, heatwaves didn't dominate the pre-monsoon period. This year, a good number of them swept through the country, especially from March to May. At least four of them were strong and lasted for a long time.”
Dhaka and other densely-populated major cities like Khulna, Barishal and Rajshahi are gradually becoming prone to heatwaves, according to Mannan.
"Sylhet was among the places that would never experience heat waves due to the local weather and heavy rains. But a recent analysis showed that Sylhet is also becoming vulnerable to heatwaves,” the meteorologist said.
This year's heatwaves expanded up to Sylhet. Chattogram seldom experienced heatwaves in the past. This year, areas from Sitakunda to Rangamati were affected. The mercury rose to 39.3 degrees Celsius."
An analysis of the daily heat index shows that all these regions are gradually facing hotter weather. The climate pattern which was eminent in the northern part of Bangladesh has now shifted to the south and south-eastern part.
Earlier, the western part of Bangladesh, including Chuadanga, Rajshahi and Khulna, would experience cold waves more frequently. However, this cycle has now shifted to the northern part in the past few years.
Rangpur and Mymensingh divisions in particular are experiencing more cold waves, the meteorologist said. “This marks a shift in the weather pattern.”
“Overall, the temperature in Bangladesh is rising gradually and it is leading to more Nor'westers, floods, flash floods, heatwaves and heavy rain.”
The World Bank study, “Climate Afflictions”, finds a link between the shifting climatic conditions and the increase in respiratory, waterborne, and mosquito-borne diseases as well as mental health issues.
With further climate change predicted, more physical and mental health issues are likely to emerge, it said adding the most vulnerable are children and the elderly, and those living in large cities like Dhaka and Chattogram.
Erratic weather conditions played a key role in the 2019 dengue outbreak in Dhaka city, where 77 percent of the country’s total dengue-related deaths occurred. That year, Dhaka recorded more than three times the average February rainfall followed by high temperature and humidity between March and July.
Compared to monsoon, the likelihood of contracting an infectious disease is about 20 percent lower in the dry season.
The propensity for respiratory illnesses also rises with the increase in temperature and humidity.
For a 1°C rise in temperature, people are more likely to suffer from respiratory illnesses by 5.7 percentage points, while for a 1 percent increase in humidity, the chances of catching a respiratory infection rise by 1.5 percentage points.
The weather pattern also affects mental health. More people suffer from depression during winter while the level of anxiety disorders increases with temperature and humidity. Further, women are at higher risk than men for depression, while men are more susceptible to anxiety.
Rising temperature has both direct and indirect impacts, said public health expert Mushtuq Husain. "Bangladesh is one of the countries vulnerable to climate change. It would definitely impact public health," he said.
“The main victims of climate change are humans and animals. Earlier, we used to think that viral fever is a seasonal disease, but now we see it happening all the time. It has become unpredictable. There’ll be an increase in rainfall and both communicable and non-communicable diseases will be prevalent.”
“Due to climate change, animals will transmit their virus to humans and new viruses will emerge. A virus may lead to a communicable disease and sometimes, it may turn into a pandemic. There’ll be a surge in insect-borne diseases like dengue, chikungunya, malaria or filaria,” he added.
AKM Saiful Islam, a professor at BUET's Institute of Water and Flood Management, tied the prevalence of diseases such as diarrhoea and cholera to the regular heatwaves gripping the country.
"Scientists believe that the effects of climate change will lead to outbreaks of diseases such malaria and dengue,” said the BUET professor.
Climate change could also have a profound impact on agriculture as the phenomenon has increased water salinity and the extraction of groundwater due to dry conditions, according to experts.
The rising sea level, increased salinity in the water, smaller harvests and deforestation are evident as an aftereffect of climate change, Mushtuq said.
People from the marginal groups will face the biggest problem of all -- a lack of nutrition. The authorities must plan their initiatives around public health issues, according to him.
Besides the global efforts, Bangladesh can deal with outbreaks of infectious and other climate-sensitive diseases by strengthening its healthcare system, according to experts.
Also, awareness building and community mobilisation through the creation of self-help groups will help the country address the physical and mental health issues more effectively.
Prof Saiful warned that a 1 degree Celsius rise in temperature is already taking a heavy toll on many parts of the country and the situation will only worsen in the future.
“We can see extreme weather events all over the world. Floods, droughts, wildfires, landslides, cyclones -- these are all intensifying and sometimes taking on stronger forms. In Bangladesh, we have seen two major floods and two cyclones in the last five years.
"We are also experiencing extreme heat and heatwaves, while the pattern of the monsoon is changing. The monsoon sets in later than before and also lasts longer. There are so many things we are already observing. We will see more in the future."
As world leaders converged in the Scottish city of Glasgow for a COP26, a UN conference critical to averting the most disastrous effects of climate change, a report by the World Meteorological Organisation (WMO) made grim findings on the extent of global warming.
The global mean sea level rose by a factor of two within a period of 10 years, rising by 2.1mm per year between 1993 and 2002 and 4.4mm per year between 2013 and 2021, according to the WMO.
Highlighting the potential effects of the rising sea level, he said, "Some areas in the country will be underwater. Salinity is increasing and this will affect public life. The tidal surges will also be higher than before and the amount of rainfall will increase along with the intensity of cyclones."
"As the volume of rainfall increases during the monsoon, areas with less rainfall during the winter [Barendra, Rajshahi] may experience a moderate drought," he added.
The rains will cause erosion which in turn will result in the flooding of the coastal areas. Urban floods will also affect the protected areas of the city, while there will likely be more landslides in mountainous areas and flash floods will frequently sweep across the Haors (backswamps), he warned.
[Written in English by Sabrina Karim Murshed; edited by Turaj Ahmad]