Climate change could leave millions of people vulnerable to dangerous heat

New research published in the journal Nature Sustainability suggests that current climate policies will result in over a fifth of the global population being exposed to dangerously hot temperatures by 2100. Despite the commitment made in the Paris Agreement to keep global warming well below 2°C compared to pre-industrial levels, projections indicate that the Earth will warm by 2.7°C by the end of the century.

The study, led by researchers from the Global Systems Institute at the University of Exeter and Nanjing University, analyzed the impact of this level of warming on human populations. It found that approximately 60 million people already live in areas with average temperatures of 29°C or higher, which are considered dangerous. Furthermore, if global warming reaches 2.7°C, an estimated 2 billion people, which accounts for 22% of the projected population in 2100, would be exposed to such extreme heat.

The research emphasizes the significant potential of decisive climate policies in mitigating the human costs and inequalities associated with climate change. By limiting global warming to 1.5°C, only 5% of the population would be exposed to dangerous heat, thereby saving a sixth of humanity from these extreme conditions compared to the scenario of 2.7°C warming.

The study also highlights the inequities of the climate crisis, noting that the lifetime emissions of just 3.5 average global citizens today, or approximately 1.2 U.S. citizens, would expose one future individual to dangerous heat. This inequality arises because the people affected by future extreme heat reside in regions where current emissions are about half of the global average.

In worst-case scenarios of 3.6°C or even 4.4°C global warming, the researchers warn that half of the world’s population could be living outside the “climate niche,” which poses an existential risk.

Professor Tim Lenton, director of the Global Systems Institute at the University of Exeter, emphasizes that while the costs of global warming are often discussed in financial terms, this study sheds light on the immense human cost of failing to address the climate emergency. For every 0.1°C of warming beyond current levels, approximately 140 million more people will be exposed to dangerous heat. This underscores both the scale of the problem and the critical importance of taking decisive action to reduce carbon emissions. By limiting global warming to 1.5°C instead of 2.7°C, the number of people exposed to dangerous heat in 2100 could be reduced by a factor of five.

Defining the niche

New research indicates that human population density has historically peaked in regions with an average temperature of around 13°C, with a secondary peak occurring at approximately 27°C, particularly in monsoon climates like those found in South Asia. Crop and livestock density, as well as wealth measured by GDP, also exhibit similar patterns, with peaks at around 13°C.

However, the study reveals that climate change has already pushed more than 9% of the global population (over 600 million people) outside this “niche.” Most of these individuals previously resided near the cooler peak of 13°C and are now in a transitional zone between the two peaks. While not dangerously hot, these areas tend to be drier and historically unable to support dense human populations, posing challenges for livelihoods.

On the other hand, the study highlights that the majority of people projected to be outside the niche due to future warming will face exposure to dangerous heat. Such extreme temperatures have been linked to a range of detrimental effects, including increased mortality, reduced labor productivity, impaired cognitive performance and learning, adverse pregnancy outcomes, decreased crop yields, heightened conflict, and the spread of infectious diseases.

Although certain cooler regions may become more habitable as a result of climate change, population growth is expected to be highest in areas at risk of dangerous heat, particularly in countries like India and Nigeria.

The research findings further indicate:

  • Exposure to dangerous heat begins to rise significantly at 1.2°C of global warming (slightly above the current level) and increases by approximately 140 million people for every 0.1°C of further warming.
  • With a future population of 9.5 billion people, India would have the highest number of individuals exposed to dangerous heat at 2.7°C of global warming—over 600 million. However, this figure would be significantly lower at approximately 90 million if warming is limited to 1.5°C.
  • Nigeria would have the second-largest population exposed to heat at 2.7°C of global warming—over 300 million. At 1.5°C warming, this number would be less than 40 million.
  • India and Nigeria already experience “hotspots” with dangerous temperatures.
  • At 2.7°C of warming, nearly 100% of certain countries, including Burkina Faso and Mali, would have dangerously hot conditions for humans. Brazil would have the largest land area exposed to dangerous heat, despite very little area being affected at 1.5°C. Australia and India would also witness significant expansions in the area exposed to extreme heat.

The study, conducted by researchers from various institutions such as the Global Systems Institute at the University of Exeter, the Potsdam Institute for Climate Impact Research, the International Institute for Applied Systems Analysis, and several universities, emphasizes that taking rapid action to reduce greenhouse gas emissions can prevent the worst impacts projected by these findings.

The researchers propose that their calculations, which highlight the discrepancy between the economic costs of carbon emissions and their impact on human well-being, should prompt new, unconventional considerations about justice in addressing the climate crisis.

The study underscores the racialized nature of projected climate impacts and calls for a transformative shift in policy thinking regarding the urgency of decarbonization efforts. Urgent action is needed to cut greenhouse gas emissions and mitigate the escalating effects of dangerous heat on global populations, as highlighted by the Earth Commission at Future Earth and the Global Systems Institute.

The University of Exeter’s Global Systems Institute has been actively working on climate solutions and has identified potential “positive tipping points” that could accelerate action. A recent report from the institute highlighted three “super-leverage points” that have the potential to trigger a cascading effect toward decarbonization.

Source: University of Exeter

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