HONG KONG — Some 2 billion people, or more than a fifth of the global population, will be exposed to dangerously hot temperatures by the end of this century if the world reaches 2.7°C of global warming, according to research that outlines the human cost of climate change.

Reducing global warming from 2.7°C to 1.5°C, as sought under the Paris Agreement, could reduce the population exposed to unprecedented heat — those living under an average annual temperature of 29°C or higher, by five-fold, protecting a sixth of the world’s population by 2100, according to the study by researchers at the Global Systems Institute at the University of Exeter and Nanjing University, which was published in the peer-reviewed journal Nature Sustainability on Monday (May 22).

Compared to previous studies, which often estimated the cost of global warming in financial terms, this study highlights “the phenomenal human cost of failing to tackle the climate emergency”, according to Tim Lenton, professor and director of the Global Systems Institute.

“For every 0.1 degrees of warming above present levels, about 140 million more people will be exposed to dangerous heat,” said Prof Lenton. “This reveals both the scale of the problem and the importance of decisive action to reduce carbon emissions.”

The study starkly detailed how the narrow subset of earth’s inhabitable climate, the “human climate niche”, is rapidly shrinking, putting millions in the future at risk.

About 600 million people, or 9 per cent of the current world population, are already exposed to dangerous heat conditions, the researchers found. If global warming reaches 3.6°C or even 4.4°C, half of the world’s population could be left outside the climate niche, posing what the researchers call an “existential risk”.

“The vast majority of people set to be left outside the niche due to future warming will be exposed to dangerous heat,” said Xu Chi, professor of Nanjing University who co-authored the paper.

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 spread of infectious diseases, he said.

The study also highlighted the inequity of climate crisis, as those living in the lowest emitting areas today could be at the highest risk to dangerous heat.

At 2.7°C, almost 100 per cent of some countries including Burkina Faso and Mali will be dangerously hot for humans, the study found. India and Nigeria will be the two countries with the greatest population exposed to this level of global warming, over 600 million and over 300 million, respectively.

It also found that the lifetime emissions of 3.5 average global citizens today — or just 1.2 US citizens — can expose one future person to dangerous heat.

The researchers hoped their study could help bridge the gap in people’s current understanding of climate change and work as a firm reminder of the urgent need for decisive action to rapidly reduce carbon emissions ahead of the Bonn Climate Change Conference hosted by the United Nations Framework Convention on Climate Change in Germany next month.

These new findings “should inspire a policy sea-change in thinking around the urgency of decarbonisation efforts as well as in the value of massively upshifting global investment into the frontlines of climate vulnerability,” said Mr Ashish Ghadiali of Global Systems Institute.

Global temperatures are likely to surge to record levels in the next five years, fuelled by heat-trapping greenhouse gases and a naturally occurring El Nino event, according to the World Meteorological Organization last week.

El Nino brings hotter and drier weather with it and already some countries in Asia have seen record temperatures in April.

According to Ms Hannah Lee, head of APAC ESG equity research at JPMorgan, as the world faces El Nino conditions, adaptation as an investment theme will come into focus. Equity investors who have previously focused largely on mitigation investing will pay more attention to investment ideas that help the world live with the effects of climate change, she said.

The demand for adaptation funding will be huge and continues to increase, with estimated annual financing needs in the range of US$160 billion (S$216 billion) to US$340 billion by 2030, rising to US$315 billion to US$565 billion by 2050, according to JPMorgan.

Finance flows to developing countries to implement adaptation was US$29 billion in 2020. SOUTH CHINA MORNING POST