According to recent research, more than a fifth of humanity would be exposed to dangerously high temperatures by 2100 as a result of current climate policies.
Despite the Paris Agreement pledge to keep global warming well below 2°C (compared to pre-industrial levels), current policies are projected to result in 2.7°C warming by the end of the century.
Researchers from the Global Systems Institute, University of Exeter, the Earth Commission, and Nanjing University led a new study that evaluated what this would entail for the population living outside the “climate niche” where our species has thrived.
It says about 60 million people are already exposed to dangerous heat (average temperature of 29°C or higher).
And two billion 22% of the projected end-of-century population would be exposed to this at 2.7°C of global warming.
In order to reduce the costs and injustices of climate change, the study emphasizes the “huge potential” for decisive climate policy.
Limiting warming to 1.5°C would leave 5% exposed saving a sixth of humanity from dangerous heat compared to 2.7°C of warming.
The analysis also reveals that one future individual is exposed to deadly heat by the lifetime emissions of just 1.2 US citizens or the 3.5 average worldwide citizens living today. Given that these people would live in areas where current emissions are only about half as high as the global average, this illustrates the injustice of the climate catastrophe.
In “worst-case scenarios” of 3.6°C or even 4.4°C global warming, half of the world’s population could be left outside the climate niche, posing what the researchers call an “existential risk.”
“The costs of global warming are often expressed in financial terms, but our study highlights the phenomenal human cost of failing to tackle the climate emergency,” said Professor Tim Lenton, director of the Global Systems Institute at the University of Exeter.
“For every 0.1°C of warming above present levels, about 140 million more people will be exposed to dangerous heat.”
“This reveals both the scale of the problem and the importance of decisive action to reduce carbon emissions.”
“Limiting global warming to 1.5°C rather than 2.7°C would mean five times fewer people in 2100 being exposed to dangerous heat.”
Defining the niche
Human population density has historically peaked in places with an average temperature of about 13°C, with a secondary peak at about 27°C (monsoon climates, especially in South Asia).
The density of crops and livestock follow similar patterns, and wealth (measured by GDP) peaks at about 13°C.
Mortality increases at both higher and lower temperatures, supporting the idea of a human “niche.”
9% of the world’s population (or more than 600 million people) are now outside the niche due to climate change, even though less than 1% of humanity still lives in regions where they are at risk of hazardous heat exposure, according to the study.
“Most of these people lived near the cooler 13°C peak of the niche and are now in the ‘middle ground’ between the two peaks. While not dangerously hot, these conditions tend to be much drier and have not historically supported dense human populations,” said Professor Chi Xu, of Nanjing University.
“Meanwhile, the vast majority of people set to be left outside the niche due to future warming will be exposed to dangerous heat.”
“Such high temperatures have been linked to issues including increased mortality, decreased labour productivity, decreased cognitive performance, impaired learning, adverse pregnancy outcomes, decreased crop yield, increased conflict and infectious disease spread.”
While some cooler regions may become more habitable as a result of climate change, India and Nigeria in particular are expected to have the fastest rates of population expansion.
The study also found:
- Exposure to dangerous heat starts to increase dramatically at 1.2°C (just above current global warming) and increases by about 140 million for every 0.1°C of further warming.
- Assuming a future population of 9.5 billion people, India would have the greatest population exposed at 2.7°C global warming more than 600 million. At 1.5°C, this figure would be far lower, at about 90 million.
- Nigeria would have the second-largest heat-exposed population at 2.7°C global warming, more than 300 million. At 1.5°C warming this would be less than 40 million.
- India and Nigeria already show “hotspots” of dangerous temperatures.
- At 2.7°C, almost 100% of some countries including Burkina Faso and Mali will be dangerously hot for humans. Brazil would have the largest land area exposed to dangerous heat, despite almost no area being exposed at 1.5 °C. Australia and India would also experience massive increases in area exposed.
The research team which included the Potsdam Institute for Climate Impact Research, the International Institute for Applied Systems Analysis, and the Universities of Washington, North Carolina State, Aarhus and Wageningen stress that the worst of these impacts can be avoided by rapid action to cut greenhouse gas emissions.
Speaking about the conception of their idea, Professor Marten Scheffer, of Wageningen University, said: “We were triggered by the fact that the economic costs of carbon emissions hardly reflect the impact on human wellbeing.”
“Our calculations now help bridging this gap and should stimulate asking new, unorthodox questions about justice.”
Ashish Ghadiali, of Exeter’s Global Systems Institute, said: “These new findings from the leading edge of Earth systems science underline the profoundly racialised nature of projected climate impacts and should inspire a policy sea-change in thinking around the urgency of decarbonisation efforts as well as in the value of massively up-shifting global investment into the frontlines of climate vulnerability.”
The Open Society Foundations funded the research and the paper is also an output of the Earth Commission convened by Future Earth, the Earth Commission is the scientific cornerstone of the Global Commons Alliance.
Wendy Broadgate, Executive Director of the Earth Commission at Future Earth, said: “We are already seeing effects of dangerous heat levels on people in different parts of the world today. This will only accelerate unless we take immediate and decisive action to reduce greenhouse gas emissions.”
The Global Systems Institute at the University of Exeter has been working on climate solutions and has discovered “positive tipping points” to speed up the action. A recent paper revealed three “super-leverage points” that might start a cascade of decarbonization.
