Extreme heat will rise rapidly as the 1.5°C threshold is crossed, potentially causing half the world’s population to live in extreme heat by 2050, 

Shiny, glass-facade buildings are a symbol of modernisation and growth, but such buildings are dangerously vulnerable in a rapidly warming world, as they trap solar heat and will face much greater heat stress over their lifetime than expected, according to a new study from Oxford University. 

This disconnect between modern aesthetics and thermal reality is emblematic of a wider adaptation gap. While glass towers lock in high energy demand, the report’s findings focus on the more urgent scale of human exposure, tracking how billions in the most vulnerable communities will be forced to navigate a world of unprecedented heat.

Almost half the world’s population, almost four billion people, will be living with extreme heat by 2050 if the world reaches 2°C of global warming above pre-industrial times, according to the report, a global gridded dataset published in Nature Sustainability.

By population exposure, six countries – India, Nigeria, Indonesia, Bangladesh, Pakistan and the Philippines – will have the largest populations affected by the extremes. 

As absolute heat intensity surges, 20 countries, primarily in Africa, South America, and Southeast Asia, are estimated to see the greatest absolute change in heat intensity. The hottest countries are predicted to be Central African Republic, Nigeria, South Sudan, Laos, and Brazil.

Paradoxically, colder climates will see the largest relative change. Compared to the 2006–2016 period, a 2.0°C rise would more than double “uncomfortably hot days” in Canada and Austria, with Ireland seeing a staggering 230% increase.

What are CDDs and HDDs?

The study’s results are measured in ‘cooling degree days’ and ‘heating degree days’ metrics commonly used in climate research and weather forecasting to estimate whether cooling or heating is needed to keep people within safe temperatures. 

Cooling Degree Days (CDDs) and Heating Degree Days (HDDs) are simple measures of how much heating or cooling buildings need. They compare outdoor temperatures to a reference temperature (often around 18°C). For example, a day with a mean outdoor temperature of 30 °C has 12 CDDs. Adding up all such days over a year gives the annual CDD value. A value of 3,000 CDD means that, over the year, temperatures are persistently high enough to create very large heat exposure. 

“In practical terms, 3,000 CDD signals that cooling is no longer optional or occasional — it becomes a central issue for building design, energy use, and health,” Jesus Lizana, one of the report’s authors, told Health Policy Watch. 

While the 18°C reference point helps policymakers and engineers to improve standards, ‘safety’ for the average citizen in the Global South is a far more complex equation. For a street vendor in Kolkata or the construction worker in Lagos, extreme heat isn’t just a matter of energy demand, but it’s a biological limit. 

Crossing the 1.5°C threshold means setting new public safety standards, for instance, based on wet-bulb temperatures, where humidity and heat combine to make outdoor labour life-threatening. These new standards need to ensure that adaptation strategies protect those without the luxury of living in glass buildings and air conditioning. 

The danger is 2030 not 2050 

The report’s most urgent finding is that the threat is not decades away. The most significant shifts in adaptation requirements occur in the early stages of warming, as we cross the 1.5° warming threshold.

“If we pass 1.5° around 2030 – which is likely – India will have an average CDD of 3,078. By 2050, it will have an (annual) average CDD of 3,248,” Radhika Khosla, of the Smith School of Enterprise and the Environment and an author of the report, told HPW. 

In comparison, a decade ago, between 2006 and 2016, when the world had warmed by 1 degree, India already had 2,864 CDDs annually. 

“Our study shows that India will continue to have the largest affected population globally, and that the number of extremely hot days it faces will rise exponentially as we pass 1.5°,” Khosla says. 

Global South: Hot, hotter 

Countries in South Asia and Africa are more used to extreme heat, and 18°C days are usually a rarity in the countries mentioned in South and Southeast Asia, Africa and South America. But Khosla says that doesn’t mean its impacts will be any less acute, particularly when we are talking about a significant increase in the number of “dangerously hot days”.

In the authors’ assessment, while some Indian cities already have heat action plans to improve responses when temperatures rise, implementation needs accountability as the impacts of heat intersect across development priorities, such as healthcare, energy access, productivity, and education. 

In Africa, the Central African Republic and Nigeria face an even steeper challenge, the authors point out. They will need to adapt to ever more extreme heat while building reliable energy grids, all while dealing with life-threatening heat. 

“It is worth remembering that these countries are responsible for only a fraction of the emissions that have caused climate change, raising important questions of climate justice and adaptation finance,” Khosla adds.

What should policymakers do?

The warning is clear that the adaptation to higher temperatures needs to be sped up. Most increases in CDDs occur before reaching the 1.5° threshold across the top 20 countries, indicating that the most significant shifts in adaptation requirements occur in the early stages of warming – before 2030, rather than in a steady progression. 

This dataset provides a basis for incorporating new climate data into sustainability planning and development policy. For buildings, CDD is a useful metric to estimate and design the increased demand for cooling while ensuring it is sustainable – for instance, how to deliver more air conditioning but with lower emissions and power consumption. 

“This research adds to the body of evidence that heat exposure in vulnerable communities is accelerating, in some cases faster than many have predicted,” says Luke Parsons of The Nature Conservancy. 

Low-income nations with relatively higher social vulnerability are usually the least equipped to face some of the largest increases in extreme heat. 

“Unless we move to rapidly limit global warming, we are on track to see major impacts in the short and long term,” he says.

Rethink glass high-rises

More visibly, this means that the glass high-rise buildings designed today will face much greater heat stress than expected. Building standards need to be updated to avoid locking in high energy use, overheating risks and costly retrofits later. 

“This is especially relevant for glass-facade high-rises, which have become symbols of growth but often perform poorly in hot conditions. Large glass areas trap solar heat, increasing cooling demand and vulnerability during heatwaves,” Jesus Lizana told HPW. 

Inclusive adaptation requires looking past the shiny skyscrapers to the neighbourhoods where most people actually live. In dense, low-income urban areas, the ‘Urban Heat Island’ effect can make local temperatures several degrees hotter than official weather station readings. 

Real adaptation, for the majority, looks like ‘cool roofs’ for informal housing, greater urban tree canopies to provide natural shade, and improving the energy grid to prevent the power outages that turn modest homes into ovens. The Oxford data shows that the most vulnerable communities are already on the clock.

The glass high-rise is emblematic of a larger disconnect: a modernisation strategy that prioritises aesthetics over global warming reality. For the billions living in informal housing or working outdoors, adaptation cannot be a luxury. 

The message for the Global South is clear. Policy choices made today must be built for the 1.5°C reality of 2030, not the cooler world of the past.

Image Credits: Erika Plepyte/ Unsplash, Shashi Yadav/ Unsplash.