Heatwave: This Is How Dangerous Extreme Heat Is to Humans

The headlines coming out of India as it grappled with an extreme heatwave the past few days have been alarming.

A weather station in Delhi recorded a temperature of 52.9 degrees Celsius, which, if confirmed, would be a national record. Animals have died, students have fainted at schools and drinking water taps have dried up. A labourer reportedly died of heatstroke on Thursday.

It's not only India. Mexico is in the grip of a heatwave that has killed at least 48 people since March. The "heat dome" hovering over the central American nation is set to move to the United States in coming days.

Heat is the silent killer that is responsible for more deaths than any other natural disaster. Several severe European heatwave in recent decades, including last summer, have claimed tens of thousands of excess deaths.

Death tolls in developing countries are not properly counted and probably much larger.

But worse is coming and we need to prepare for it.

The average surface temperature on Earth is now at its highes

The headlines coming out of India as it grappled with an extreme heatwave the past few days have been alarming.

A weather station in Delhi recorded a temperature of 52.9 degrees Celsius, which, if confirmed, would be a national record. Animals have died, students have fainted at schools and drinking water taps have dried up. A labourer reportedly died of heatstroke on Thursday.

It's not only India. Mexico is in the grip of a heatwave that has killed at least 48 people since March. The "heat dome" hovering over the central American nation is set to move to the United States in coming days.

Heat is the silent killer that is responsible for more deaths than any other natural disaster. Several severe European heatwave in recent decades, including last summer, have claimed tens of thousands of excess deaths.

Death tolls in developing countries are not properly counted and probably much larger.

But worse is coming and we need to prepare for it.

The average surface temperature on Earth is now at its highest level since records began and probably before the last ice age.

Recent heatwave show clear fingerprints of global warming, more so than any other climate change impact such as flood or drought. And global warming will continue at least until we reach net zero.

There is a fundamental limit to the body's coping ability: it is a fixed goalpost.

Research in 2010 demonstrated that a 'wet-bulb' temperature of 35 degrees Celsius or higher would make it impossible for humans to exhaust metabolic heat, due to our fixed core body temperature.

It proposed this was an effective survivability limit. 

The wet-bulb temperature measures the ability to cool by evaporation; it equals normal temperature if relative humidity is 100 percent, and otherwise is lower. 35C is extreme — most places on Earth never experience wet bulbs above 30C. 

But enough global warming could push heatwave in many areas past 35C. This upended the widely held assumption at the time that humans could adapt to any amount of increased heat, i.e., that the goalposts would move. This goalpost will not.