The climate crisis is pushing tropical regions of the planet to the limits of human habitability, with rising heat and humidity threatening to plunge much of the world’s population into potentially lethal conditions, new research has found.
If governments are unable to control global warming at 1.5ºC above the pre-industrial era, areas of the tropical strip that stretches on both sides of the equator are in danger of becoming a new environment that will reach “the limit of adaptation human “, warns the study.
The ability of humans to regulate body heat depends on the temperature and humidity of the surrounding air. We have a core body temperature that remains relatively stable at 37 ° C (98.6 ° F), while our skin is cooler to allow heat to flow out of the inner body. But if the temperature of the wet bulb – a measure of the temperature and humidity of the air – exceeds 35 ° C, the high temperature of the skin means that the body is unable to cool itself, with potentially fatal consequences.
“If it’s too humid, our bodies cannot cool with the evaporation of sweat – that’s why moisture is important when considering habitability in a warm place,” said Yi Zhang, a Princeton University researcher who led the new study, published in Nature Geosciences. “The high core temperatures of the body are dangerous or even lethal.”
The research team analyzed various historical data and simulations to determine how the extremes of wet bulb temperature will change as the planet continues to heat up, finding that these extremes in the tropics increase at the same rate as the average tropical temperature.
This means that the increase in world temperature will need to be limited to 1.5 ° C to avoid the risk of areas in the tropics that exceed 35 ° C in wet bulb temperature, which is so called because it is measured by a thermometer that has its bulb wrapped in a damp cloth, helping to mimic the ability of humans to cool the skin by evaporating sweat.
Dangerous conditions in the tropics will occur even before the 1.5 ° C limit, however, with the newspaper warning that 1 ° C of extreme increase in wet bulb temperature “could have an adverse health impact equivalent to that of varying degrees of increase temperature ”. The world has already warmed by about 1.1 ° C on average due to human activity and, although governments in the Paris climate agreement have promised to keep temperatures at 1.5 ° C, scientists have warned that this limit could be breached within one of each.
This has potentially dire implications for a large part of humanity. About 40% of the world population currently lives in tropical countries, with this proportion set to expand to half the global population by 2050 due to the large proportion of young people in the region. Princeton’s research focused on latitudes found between 20 degrees north, a line that cuts through Mexico, Libya and India, up to 20 degrees south, through Brazil, Madagascar and northern Australia.
Mojtaba Sadegh, a climate risk expert at Boise State University, said the study does “a great job” in looking at how rising temperatures “can make parts of the tropics uninhabitable in the absence of considerable infrastructure investments” .
“If that limit is breached, infrastructure like fresh air shelters is absolutely necessary for human survival,” said Sadegh, who was not involved in the research. “Considering that a large part of the impacted area consists of low-income countries, providing the necessary infrastructure will be a challenge.”
“Theoretically, no human being can tolerate a wet bulb temperature above 35C, no matter how much water they drink,” he added.
The study is just the latest scientific warning about the serious dangers of heat. Extreme heat waves can push parts of the Middle East beyond human capacity, the scientists found, with rising temperatures also posing huge risks to parts of China and India.
The global number of potentially life-threatening humidity and heat events doubled between 1979 and 2017, the survey determined, with the next few decades set to see up to 3 billion people pushed beyond the historical temperature range in which humans have survived and thrived in the past 6,000 years.