AC exhaust units are a common feature of urban landscapes in many parts of Asia, clinging like limpets to towering apartment blocks in Hong Kong or tucked in a cross formation between the windows of a building in Cambodia.

They offer relief from temperatures that have toppled records in recent weeks, with many countries in the region hitting 40 degrees Celsius (104 Fahrenheit) or higher.

Scientists have long warned that human-induced climate change will produce more frequent, longer and more intense heatwaves.

Only 15 percent of homes in Southeast Asia have air-conditioning, according to a 2019 report by the International Energy Agency (IEA).

But that figure obscures vast variations: ranging from around 80 percent installation in Singapore and Malaysia, to less than 10 percent in Indonesia and Vietnam, the IEA said.

Forecasts suggest that higher temperatures and better wages could see the number of air-conditioning units in Southeast Asia jump from 40 million in 2017 to 300 million by 2040.

That would stretch local electricity capacity, which is already struggling under current conditions.

Myanmar is producing only about half the electricity it needs each day, with the junta blaming weak hydropower because of scant rains, low natural gas yields and attacks by its opponents on infrastructure.

Thailand has seen record power demand in recent weeks, as people retreat indoors to cooled homes or businesses.

Air-conditioning is already responsible for the emission of approximately one billion metric tons of carbon dioxide per year, according to the IEA, out of a total of 37 billion emitted worldwide.

Still, cooling options like air-conditioning are a key way to protect human health, especially for those who are most vulnerable to the effects of extreme heat: children, the elderly and those with certain disabilities.

With demand surging, dozens of countries last year signed up to the United Nations' Global Cooling Pledge, a commitment to improve the efficiency of air conditioners and reduce emissions from all forms of cooling.

Some countries have been trying to reduce the impact of cooling for years.

Since 2005, Japan has encouraged office workers to ditch ties and jackets so air conditioners can be kept at 28 degrees Celsius.

The annual "Cool Biz" programme took on new significance during power shortages in 2011 following the shutdown of nuclear plants after the Fukushima disaster.