Wet bulb temperatures are breaching safe levels and the consequences will be tragic

Wet bulb temperature is a measure of the heat stress experienced by humans due to high temperatures and humidity. It is the lowest temperature that can be achieved through evaporative cooling of a wet surface. It is measured by covering a thermometer’s bulb with a damp cloth. The wet bulb temperature is important metric because there is a threshold beyond which humans are unable to cool their bodies by evaporation - sweating - alone. Once the wet bulb temperature passes the safe threshold it inevitably means an increase in heat-related illnesses and deaths.

Wet bulb temperature issues have been known about for more than a century. Above 31°C it is impossible for humans to undergo any exertion - working, running, etc. - whilst at 35°C death occurs within a matter of hours.

Global warming is on track to raise wet bulb temperatures above 35°C on a more and more frequent basis. The arrival of the El Niño weather system will mean that extremes which have only been previously reached in areas of Northern India and Pakistan, will spread south into the Indian peninsular and north through Asia and even into Southern Europe.

The dangers of wet bulb temperatures are becoming more apparent as global temperatures continue to rise. The effect of rising carbon dioxide concentrations in the atmosphere has increased the rate at which temperatures are increasing. Whilst we continue to dump greenhouse gases into the atmosphere the rate on increase will continue to accelerate and the impact will be felt in more areas around the world.

For richer nations that may mean turning up the air conditioning during the summer months, but for those who have done the least to contribute to the problem, this means a growing threat to life.