Explained | Bangladesh Experiences Sizzling Heatwave: What Factors Causing It And Its Impacts?

A heatwave is currently being experienced by millions of Bangladeshis, with temperatures consistently hovering around 40 degrees Celsius, significantly higher than the country's average maximum of 33 degrees during April.

The severe heatwave in Bangladesh has led to school closures, disruptions in agriculture, and increased risks of heat stroke and other health complications, as reported by The Daily Star.

Bangladesh Sizzling Heatwave: What Factors Causing It And Its Impacts?

The prevailing severe heatwave in Bangladesh is highlighted by concerns as climate change is seen to be spinning out of control. Heatwaves are recognized as one of the most dangerous manifestations of climate change. The occurrence of deadly heatwaves would have been all but impossible without climate change, which is accelerating the intensity, duration, and severity of heatwaves, as per the local newspaper report.

Furthermore, Bangladesh's geographical location in the tropical region amplifies the effects of climate change. Despite contributing only a tiny fraction of global carbon emissions-0.56 percent, according to one count-Bangladesh is suffering disproportionately from their effects.

Historical data reveals that the average daytime temperatures in Dhaka have risen by approximately 2.75 degrees over the past two decades, much higher than the global average of around 1.2 degrees and already exceeding the Paris Agreement's elusive goal of keeping warming below 1.5 degrees. Experts predict that temperatures in Bangladesh will rise even more in the coming decades.

The primary reason for record heatwaves is a heat dome, which is a self-reinforcing, sprawling area of a persistent and strong high-pressure system that traps hot air in the upper atmosphere. It is called a heat dome because the trapped air in the system acts like a lid on a boiling pot.

As the high pressure forces the stationary air in the dome to sink, it gets compressed and heats up, pushing temperatures upwards. At the same time, the dome squeezes clouds away, giving the sun an unobstructed view of the ground, which then bakes in the sunlight, as reported by The Daily Star.

Consequently, heat energy quickly accumulates and temperatures rise. The heat dome leads to extreme temperatures with high humidity, without any precipitation or rainfall, and can last for weeks, making cities like Dhaka feel like ovens under the open sky. Climate change's exacerbation of heat waves is further compounded by the three-dimensional complexity of cities, disappearing lakes, and green spaces, among others, giving rise to the urban "heat island effect" that modifies some of the climatological factors in their immediate vicinity.

With the loss of evaporative cooling normally provided by trees, lakes, and exposed soil, the gain of reradiated heat from the surfaces of high-rise buildings, narrow spaces between tall structures, dark surfaces, pavements, unshaded roads, sewers, air-conditioners, and industries that generate heat as a byproduct, the mean temperature of Dhaka and other cities in the country is on the rise. While the heat island effect does not produce dramatic temperature changes, over the years the cumulative effect is noticeable.

Another effect of climate change that augments heatwaves is balmy nights. During the last 50 years or so, overnight low temperatures during summer months worldwide have been warming at a rate nearly twice as fast as afternoon high temperatures, according to the state-run National Oceanic and Atmospheric Administration (NOAA) of the US, as per media reports.

The asymmetrical warming is because the greenhouse effect, responsible for global warming, operates round the clock, and nighttime temperatures are inherently more sensitive to climate forcing. At this time of the year, Kal Baishakhi (northwestern storms), a meteorological phenomenon characterized by rapid changes in weather, with strong winds, lightning, and thunderstorms accompanied by brief torrential rainfall, usually cools down the temperature considerably, thereby bringing relief from the scorching heat.

However, the absence of Kal Baishakhi, another victim of climate change, is contributing to the oppressive heatwave. In the 1980s, the duration of an April heatwave in Bangladesh was two to three days, and the temperatures were relatively mild, hovering around the mid-30s.

Last year, the heatwave was intense, lingering for about a week and reaching a high of 42.2 degrees recorded in Rajshahi in mid-April. The Union of Concerned Scientists warns that in the next few decades, if greenhouse gas emissions continue to grow, we will see 20 to 30 days of very intense heat waves, as reported by The Daily Star.

Understanding the Impact of Heatwaves on Human Tolerance and Climate Change Response

So, what is the hottest temperature that humans can tolerate? Well as per the report shared by the Bangladeshi newspaper, the answer to this question lies in the wet-bulb temperature (WBT) of 35 degrees Celsius, which considers both heat and humidity and differs from the ambient air temperature. Here are the following other factors:

• Most warm-blooded mammals, including humans, cool themselves by converting sweat into water vapour, aiming for a constant body temperature of 37 degrees Celsius.
• If the wet-bulb temperature (WBT) exceeds 35 degrees Celsius, it can hinder the body's ability to cool down, potentially leading to life-threatening heatstroke.
• Fortunately, the wet-bulb temperature (WBT) in Dhaka, with a high temperature of 40 degrees Celsius and 45 per cent humidity, is currently at 30 degrees Celsius.
• However, if humidity levels rise to 70 per cent or if temperatures reach 50 degrees Celsius with 45 per cent humidity, the wet-bulb temperature (WBT) would surpass the critical threshold to 35.2 degrees Celsius.

Efforts to address climate change extend beyond mere technological challenges and necessitate long-term strategies to mitigate its impacts.

• Unfortunately, most strategies devised by world leaders fail to effectively target the root cause: harmful greenhouse gas emissions.
• Their inability to comprehensively address this complex issue is seen as a temporary fix.
• Moreover, as heatwaves escalate at an alarming rate, these inadequate policies and adaptation strategies will soon prove insufficient in safeguarding people and protecting global infrastructure and natural ecosystems.

The world is experiencing rising temperatures, increased aridity, altered precipitation patterns, and other unusual climate phenomena.

• The future holds decades of heatwaves, wildfires, severe storms, floods, and prolonged droughts as inevitable consequences.
• The actions taken now will determine whether we can sufficiently slow global warming to avoid the most severe impacts of climate change.
• With ethical consideration, collective action, and unwavering dedication, it is possible to mitigate global warming and ensure a habitable planet for future generations.
• However, this endeavour will require time and concerted efforts.
• In the meantime, proactive preparation for future heatwaves and support for vulnerable populations enduring extreme heat are imperative measures.