This story includes details about the impacts of climate change that may be difficult for some readers. If you are feeling overwhelmed by this crisis situation here is a list of resources on how to cope with fears and feelings about the scope and pace of the climate crisis.

In a world for the moment still committed to dangerous levels of warming, three new research studies deliver a grim warning. By the time the planetary thermometer registers a 2°C rise above the historic average, around a billion people could expect to be afflicted with extreme heat stress, according to the UK Met Office. 

At a rise of 4°C, half the planet could expect to be exposed to dangerous levels of heat and humidity.

And a second strand of strand of research considered global preparedness for the hotter, but unequal world of the next two decades: by 2040, up to 100 million households in India, Brazil, and Mexico will have to try to survive without air conditioning. Perhaps even more ominously, citizens of those countries who can afford it will drive up electricity demand, three-fold in India and Indonesia, and almost double in Mexico and Brazil. 

Those findings land at a moment when the rate of planetary warming driven by human action has no precedent in the last 24,000 years, U.S. scientists say. Even the seemingly abrupt end of the last Ice Age was slow by comparison. 

It’s a reminder that the goal of a temperature limit “well below 2°C” set by international agreement in Paris in 2015—but so far not secured by the just-ended global climate conference in Glasgow—is still vital, and literally so. Once conditions reach what meteorologists like to call a “wet bulb temperature” of about 32°C, work outdoors becomes potentially hazardous and people exposed to such temperatures are considered at “extreme risk”. 

Such findings are not new: extreme heat can kill, and in recent years scientists have repeatedly confirmed that—without drastic action—that billions could be at risk. But science is a process of attrition. Researchers continually question their own assumptions and re-examine evidence in the pursuit of ever more precise conclusions, and UK Met Office scientists, working with international colleagues in an EU-funded project, are only the latest to look once again at those landscapes most at hazard from tomorrow’s heat extremes. 

The result? A series of maps that highlight those regions most at risk from the potentially lethal combination of rising heat and soaring humidity—the so called wet bulb measure—and from other climate hazards that become even more hazardous at global temperatures rises of between 2°C and 4°C. These are river flooding, the risk of wildfire, drought, and food insecurity.

“This combined analysis shows the urgency of limiting global warming to well below 2°C,” warned project lead Richard Betts of the University of Exeter and the Met Office. “The higher the level of warming, the more severe and widespread the risks to people’s lives, but it is still possible to avoid these higher risks if we act now.” 

“Our maps show that some regions will be affected by multiple factors,” added Andy Wiltshire, who heads earth system and mitigation science for the Met Office. “Perhaps unsurprisingly, parts of the tropics are most affected, with countries like Brazil and Ethiopia potentially facing impacts from four of the hazards. Rapid emission reductions are required if we are to avoid the worst consequences.” 

Those with resources will find ways to combat the increasing extremes of heat and humidity: European and Brazilian scientists report in the journal Nature Communications that within the next 20 years, 85% of households in Brazil will be fitted with air conditioning systems, as will 61% of Indonesia families and 69% of homes in India. But that will still leave somewhere between 64 million and 100 million households exposed to uncomfortable and potentially harmful extremes. 

And ever-higher temperatures, and ever more frequent heat waves, are increasingly likely. U.S. researchers read a story told in the chemical signatures of millennia of marine sediments and report in the journal Nature that both the rate of change in global warming and its magnitude surpass any such changes since the last interglacial, deep in the last Ice Age, 24,000 years ago. The world has indeed been warming, imperceptibly, for the last 10,000 years, but over almost all that time the shift has been about half a degree Celsius: the rise of more than 1°C in the last century or so is firmly pinned on greenhouse gas emissions and the retreat of the polar ice sheets. 

“The fact that today we are so far out of bounds of what we might consider normal is cause for alarm and should be surprising to everybody,” said study lead Matthew Osman of the University of Arizona.