Imagine feeling so hot that you can barely move or breathe; that despite burning up inside, it is too humid to sweat, so your body can’t cool down. Imagine knowing that—unless you can find an air-conditioned refuge—you have less than six hours to live.

Even the blistering June heatwave across Europe that smashed records and sent temperatures soaring to almost 46°C in France, did not bring about such a nightmare scenario. As we continue to pump our atmosphere full of carbon, however, it is a horror that hundreds of millions may face later this century.

In fact, such inescapable heat and humidity is nothing less than the logical end product of an ominous pattern of extreme weather that is making itself ever more conspicuous.

When a once-stable climate system begins to break down, the signs become clear for all to see.

An age of extremes

More and more, the weather swings wildly from one extreme to another, smashing records on an almost daily basis that have stood for many decades, even centuries.

Over the last twenty years, in particular, floods and droughts have become more prevalent and more severe, storms more powerful, and cold snaps more intense.

But the most obvious symptom that climate collapse is accelerating can be found in the increasingly frequent, longer lasting and pernicious heat-waves that are now a global phenomenon.

Worldwide, twenty of the hottest years on record have occurred in the last twenty-two, so this should really come as no surprise to anyone.

The blistering Saharan heat that clothed Europe last week saw records obliterated as temperatures came within a hair’s breadth of an all-time high 46°C in France and reached more than 44°C in Spain. June temperature records also fell in Germany, Poland and the Czech Republic.

Five of the hottest European summers of the last five hundred years have roasted the continent since the beginning of the century—so this latest heatwave simply flags up a trend that will become ever more apparent as the atmosphere becomes increasingly carbon drenched.

The impact of climate change

The fact is that last week’s heatwave was made between five and 100 times more likely as a consequence of the climate emergency. It also builds on the global heatwave of 2018, which saw unprecedented heat across four continents, the close to 50°C temperatures inflicted upon Australia in January, and the extraordinarily warm February in the UK.

Europe has been better prepared for the recent sweltering conditions than during previous heatwaves, taking lessons from the 2003 hothouse conditions that claimed 70,000 lives across the continent.

But while opening cool rooms inside public buildings and setting up water fountains and water sprays are admirable initiatives, such measures will do nothing to mitigate the deadly impact of the humid heatwaves to come.

Heat and humidity

We are probably all familiar with the fact that an amalgam of high temperatures and extreme humidity makes it feel far hotter than dry heat. While temperature alone is measured using a familiar—or dry bulb—thermometer, the combination of heat and humidity is measured on a so-called wet-bulb thermometer, which is, effectively, an ordinary thermometer encased in a wet cloth.

Because heat is absorbed by the water and carried off in passing air, wet-bulb temperatures are lower than those measured on a normal dry-bulb thermometer.

As our world continues to heat up, the key wet-bulb temperature to look out for is 35°C. This flags the onset of a heat and humidity combo at which the human body can no longer lose heat through sweating.

In such circumstances, anyone without access to air conditioning—however young or fit—has only six or so hours to live, whether sheltering in the shade or not. Such sustained heat-death circumstances have yet to emerge.

Yet it can only be a matter of time before this critical threshold is reached, bringing the potential for massive death tolls in the hottest parts of our world.

In July 2015, at Bandar Mahshahr, Iran, the combination of 46°C temperatures and 50 percent humidity brought the wet-bulb temperature within a whisker of 35°C.

An uninhabitable world?

Research makes clear that as the century progresses—and under a business as usual emissions scenario—more and more of the planet will come under severe threat from such malignant heat, in particular the Middle East, South and South East Asia and China. Ground zero looks like being China’s northern plain where, today, four hundred million people toil in the country’s agricultural heartland.

By the second half of the century, fatal humid heatwaves are predicted to strike the region repeatedly, effectively making China’s breadbasket uninhabitable.

With 2019 set to be a scorcher, urged on by El Niño conditions in the Pacific, maybe this will be the year when the 35°C threshold is finally achieved. If this happens, we will have our first taste of what it will be like when parts of the world that brought forth and shaped our species finally become off limits to us.