5 January, 2020
5 January, 2020
Deadly heatwaves
Hot and humid heatwaves predicted
You may already have already been through a heatwave. Relentlessly hot temperatures lasting over several days, with nights too hot to get any rest may sound all too familiar.
For many it's exhausting, and for the young, old or sick, heatwaves can easily become dangerous.
What makes a heatwave so dangerous is the combination of heat and humidity. The heat raises the body temperature, the humidity makes it impossible to cool down by sweating.
This combination of heat and humidity is shown by something called the wet bulb temperature. It is literally measured by wrapping a thermometer in a wet cloth.
The wet bulb temperature of 35 °C (95 °F) is the limit for human endurance. After that point, our bodies cannot cool down. In a few more hours body temperatures rise to 40 °C (104 °F), and the heat becomes unsurvivable.
It is these kind of temperatures that are forecast for the later part of this century. By 2100, scientists are predicting heatwaves that will reach and exceed survivable wet bulb temperatures, and that it may affect billions of people.
The scary thing is how common those deadly conditions are already
75% of the world population affected
Professor Camilo Mora, associate professor at University of Hawaii and his team of researchers looked at past records of heatwaves around the world, and discovered what they call "the deadly threshold". This is the point at which temperatures and humidity levels become too high for people to survive. They then forecast when and where that would occur as the world gets hotter over the rest of the century.
The results are grim. The researchers say, if we continue to emit greenhouse gases at current levels, "By 2100, almost three-quarters of the world’s human population could be exposed to deadly climatic conditions."
Deadly heat forecast for 2100,
Camilo
Mora and colleagues – Global risk of deadly heat
The good news is still bad. Even if we found a way to remove greenhouse gas, the same scientists found that, by 2100, about a quarter of the world’s land area will exceed "the deadly threshold by more than 20 days per year" and about half the world's population will be exposed to "deadly climates".
According to Professor Camilo Mora, "we are running out of choices for the future".
"The scary thing is how common those deadly conditions are already", says co-author Farrah Powell.
Unhabitable regions
Dr Mora is not alone in his forecast for deadly heatwaves this century. A number of studies return similar results, with each study forecasting more heatwaves that exceed "the deadly threshold" — the wet bulb temperature of 35 °C (95 °F).
Of all regions, Africa will be the worst hit by heatwaves in the coming years. Scientists estimate one third of the African urban population could be exposed to lethal temperatures by 2090. For the larger cities in Western Africa, such as Lagos, scientists predict deadly heatwaves lasting several months, even if carbon emissions were brought under control.
Deadly heatwaves for Africa, Asia and the Persian Gulf,
jozuadouglas,
Pixabay
In China's highly populated heartland, home to 400 million people, in an area extending from Beijing to the north to Shanghai to the south, scientists forecast that by 2100, the region is likely to have experienced a number of "deadly heatwaves", all exceeding the lethal wet bulb temperature of 35 °C (95 °F).
The South Asian nations of Pakistan, India and Bangladesh are already experiencing major heatwaves, which will only get worse. Researchers predict temperatures approaching the 35 °C (95 °F) threshold wet bulb temperature "by the end of the century over most of South Asia." By 2100, 4% of India's massive population will have experienced deadly temperatures.
Always hot, it's no surprise that for the Persian Gulf, scientists forecast "temperature levels that are intolerable to humans". By the end of the century, the wet bulb temperature will have exceeded the deadly 35 °C (95 °F) threshold several times in the major cities of Abu Dhabi, Dubai and Doha.
Heatwaves already deadly
With each decade, heatwaves have been getting more and more lethal.
The first deadly heatwave of the century was across Europe in 2003. Unprepared for the heat, more than 70,000 lost their lives.
Just a few years later in Russia, in 2010, the worst heatwave on record was to take place. 56,000 lives were lost in heat lasting more than 40 days without a break, across a region spanning 2 million square kilometres (772,204 square miles).
Watch: Disasters — extreme heat kills thousands in Paris | BBC
In other countries heatwaves are becoming a common occurrence.
Over the period 2010-2019, Japan struggled through 11 heatwaves, more than one each year on average. While casualties have not been as high as other countries, one heatwave in 2018 left 71,266 hospitalised.
In the space of 30 years, heatwaves have become deadlier, more frequent, and more widespread.
Mega-heatwaves of the future
In the future, heatwaves are likely only to worsen. Mega-heatwaves more severe than the worst experienced so far, worse even than the Russian heatwave of 2010, are predicted to become commonplace in the future, according to an EU study.
If the world warms by an average of 4 °C (6 °F), heatwaves more extreme than the Russian mega-heatwave of 2010 are predicted for every other year, or five times a decade. This prediction covers the eastern U.S, northern Latin America and China.
Watch: Too HOT and HUMID to live: Extreme wet bulb events are on the rise | PBS Terra
For Europe, India, and across Africa, the same mega-heatwaves should take place just once a decade, according to EU scientists.
The scientists also looked at levels of humidity during the heatwaves. They found that at 4 °C (6 °F) global warming, the combination of heat and humidity in eastern U.S., India and China is expected to reach "extreme danger" levels, every one or two years. In these conditions, sunstroke is imminent and often fatal.
The scientists involved in the study questioned whether anyone could continue to live in these regions.
Related articles
