COMMENT
CLIMATE: COULD 50°C BECOME THE NEW NORMAL?
A recent heatwave in Jacobabad, Pakistan saw temperatures hit a record 51˚C – dangerously close to the limit of human survivability
More and more heatwave records are shattered every year. Last month, we saw temperatures max out at around 51˚C in central Pakistan, while last year saw a nearly 5˚C toppling of the previous temperature record in western Canada. For some of India’s current heatwaves, we have estimated that climate change has made them 100 times more likely, and by the end of the century, we predict that heatwave temperatures of 50˚C will be an annual occurrence in the region. The numbers vary depending where you are on the globe, but one thing we can be sure about: more extremes are coming.
The feeling of being hot or cold doesn’t simply depend on temperature, but a range of weather conditions.
Humidity, wind speed, and solar radiation can all add or subtract from our perceived temperature, and in certain combinations, they can be deadly.
WET BULB, DRY BULB
At the heart of this combination is ‘dry-bulb temperature’. This is what we normally think of when we say temperature, and what you would measure if you stuck a thermometer above your head and read off the mercury. But meteorologists often prefer to use a ‘felt temperature’, known as wet-bulb temperature, which is also measured with a thermometer but wrapped in a wet cloth, to mimic many of the same heat transfers that are regulated by our bodies.
Most of us know the uncomfortable feeling of being unable to cool down on a humid night – the same mechanisms are at play here. Physiologically, this makes sense. Humans, and indeed all mammals, sweat to cool down, a process of losing moisture from our bodies. If the humidity is too high, the sweat cannot move from our skin, so this cool-down mechanism is prohibited.
We know the human tolerance level pretty well – it is a wet-bulb temperature of 35˚C. At this point, humans cannot survive for more than a couple of hours because we can no longer transfer heat from our body to the environment. This might not sound like much, but the numerical value of the wet-bulb is always lower than that of the dry-bulb (except at 100 per cent relative humidity). This means a 35˚C wet-bulb temperature can easily equate to an over 50˚C dry-bulb temperature, even at moderate humidity levels.
So, have we ever exceeded a 35˚C wet-bulb temperature threshold? The answer is yes, but very rarely. There have only been about 10 reported cases, all in the Middle East, in and around India, in Australia and in Mexico. Even when wet-bulb temperatures do not reach this high, the large, densely packed cities in these regions compound the heat-health problem, and so it is commonplace to see hundreds of heat-related deaths every year in some of the major urban centres.
In general, the richer and more modern the city, the less of a problem this is, and in some of the larger Middle Eastern cities they have learnt to adapt very well. Indeed, the locals in Dubai and Abu Dhabi know to dress up warm in the height of summer, because they travel by car from building to building, with the AC maxed out and without ever needing to walk outdoors.
The poorer and more rural-based citizens of the world do not have this luxury.
But will climate change make this worse? Given the increase in temperatures, we expect more exceedances of the 35˚C survivability threshold in the future, but these cases are likely to remain rare and only occur for a few hours at a time. We expect them to be limited to locations in the tropics and subtropics, and even then only during certain years. We predict that the likelihood of these exceedances significantly diminishes if we can adhere to the Paris Agreement climate goals – that is, keeping the rise in global mean temperature below 2˚C.
“Adapting to new heat norms is inevitable, but the good news is that we already have a wealth of heat-reduction strategies available to us”
Even if temperatures do not exceed survivability limits, though, heat can still kill. Adapting to new heat norms is inevitable, but the good news is that we already have a wealth of heat-reduction strategies available to us. Even in Europe, we see many streets surrounded by tall rows of buildings, able to shade inhabitants from the penetrating sunlight. We also see buildings painted in lighter colours, reflecting the Sun’s heat and providing a cooler environment.
For countries closer to the equator, more drastic measures have been implemented. AC, where financially viable, is an excellent option, but many of the poorer countries do not have the power infrastructure to make this technology reliable. One near-universal strategy that has been shown to work is introducing more nature-based spaces, trees, and water bodies in cities. While not always feasible if your climate is not conducive to such ecosystems, where it is implemented it has been shown to include a wealth of physical and mental health benefits.
In this world of ever-increasing urbanisation, we have spent decades paving over nature – now is the time to let nature claim some of that back.
Dann is a professor of climate science at the University of Bristol’s School of Geographical Sciences.