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Limiting global warming to 1.5 degrees Celsius would save billions of lives

The specter of a dangerously hot future awaits more than a fifth of the global population by 2100, according to compelling new research. This warning comes despite pledges made under the Paris Agreement to maintain global warming well below 2°C when compared to pre-industrial levels. 

Researchers fear that existing climate policies may fail to curb the rising mercury and lead to an average global temperature increase of 2.7°C by the century’s close.

This groundbreaking study, a collaborative effort of the Global Systems Institute at the University of Exeter, Earth Commission, and Nanjing University, presents a sobering picture of what such a temperature increase could mean for humanity. 

How the study was conducted

In essence, the researchers studied the impact of this warming on the number of people living outside the “climate niche” – a term describing the conditions under which our species has thrived.

The study reveals that approximately 60 million people are currently exposed to dangerously high heat levels, defined as an average temperature of 29°C or higher. Alarmingly, should global warming reach 2.7°C, this figure is projected to swell to two billion. This represents a staggering 22% of the projected population by 2100.

However, amidst the grim statistics, the paper also underscores the significant potential of resolute climate policy to mitigate the human costs and inequities of climate change. 

Sticking to climate policy can make a huge impact

By implementing more stringent policies that limit global warming to 1.5°C, we could significantly reduce the number of people exposed to dangerous heat levels – saving a sixth of humanity from this fate compared to a scenario of 2.7°C warming.

The team went on to highlight the climate crisis’s inherent inequity. They found that the lifetime emissions of merely 3.5 average global citizens today, or just 1.2 US citizens, could expose one future person to dangerous heat. 

This stark reality gains a further dimension when considering that the regions where these future heat-exposed individuals will reside typically emit only about half of the global average today.

Worst-case scenarios of 3.6°C or even 4.4°C global warming could push half the world’s population outside the climate niche, an existential risk that researchers are urging us to avoid.

“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.

“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 human “niche”

In order to better understand this crisis, the researchers defined the human “niche.” Historically, human population density has peaked in areas with an average temperature of about 13°C, and to a lesser extent, 27°C – typically monsoon climates such as those found in South Asia. In line with this, wealth (as measured by GDP), along with crop and livestock density, follows a similar pattern.

Yet, as less than 1% of humanity currently lives in places of dangerous heat exposure, the study shockingly shows that climate change has already forced 9% of the global population (more than 600 million people) out of the niche.

“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,” explained Professor Chi Xu of Nanjing University. 

“Meanwhile, the vast majority of people projected to be pushed outside the niche due to future warming will face dangerous heat. Such high temperatures have been linked to a plethora of problems, including increased mortality, decreased labor productivity, impaired learning, adverse pregnancy outcomes, reduced crop yield, escalated conflict, and the spread of infectious diseases.”

What the researchers learned

The study also suggests that while climate change may render some cooler places more habitable, population growth is expected to spike in regions threatened by dangerous heat, notably India and Nigeria.

In a deep dive into the specifics, the research revealed that exposure to dangerous heat begins to escalate dramatically at 1.2°C above current global warming, increasing by approximately 140 million people for every additional 0.1°C of warming.

With a projected global population of 9.5 billion people, the numbers are even more concerning. At 2.7°C of global warming, India is set to bear the brunt, with more than 600 million people exposed to dangerous heat. If this warming can be limited to 1.5°C, this number could be drastically reduced to around 90 million.

Similarly, Nigeria would have the second-largest heat-exposed population at 2.7°C of global warming, with over 300 million people at risk. Reducing warming to 1.5°C would see this number decline to less than 40 million.

Even at this stage, “hotspots” of dangerous temperatures are apparent in India and Nigeria. If the globe warms by 2.7°C, nearly 100% of some countries, including Burkina Faso and Mali, will experience dangerously hot conditions. Brazil, despite having almost no areas exposed at 1.5°C, would have the largest land area exposed to dangerous heat at 2.7°C. Australia and India would also see massive increases in areas exposed to such conditions.

Avoiding crisis through rapid action

Collaborating researchers from 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 these dire consequences can be avoided through rapid action to cut greenhouse gas emissions.

Reflecting on the motivation behind their study, Professor Marten Scheffer, of Wageningen University, stated, “We were triggered by the fact that the economic costs of carbon emissions hardly reflect the impact on human wellbeing. Our calculations now help bridge this gap and should stimulate asking new, unorthodox questions about justice.”

The study’s findings offer valuable insights into the racialized nature of projected climate impacts. Ashish Ghadiali, of Exeter’s Global Systems Institute, said, “These findings from the leading edge of Earth systems science should inspire a policy sea-change in thinking around the urgency of decarbonization efforts, as well as in the value of massively up-shifting global investment into the frontlines of climate vulnerability.”

Recommendations from the research team

Funded by the Open Society Foundations, this research also serves as a cornerstone for the Global Commons Alliance through the Earth Commission. 

Wendy Broadgate, Executive Director of the Earth Commission at Future Earth, remarked, “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 is keen to identify “positive tipping points” to expedite action against climate change. A recent report from the institute highlighted three “super-leverage points” that could trigger a cascade of decarbonization.

The researchers have made their findings available in a paper titled “Quantifying the Human Cost of Global Warming,” published in the journal Nature Sustainability. This comprehensive research not only highlights the human cost of global warming but also stresses the urgent need for decisive climate policy to avert a grim future.

More about climate change and the Paris Agreement

Climate change refers to the long-term changes in temperature and typical weather patterns around the world. It’s primarily driven by human activities that release greenhouse gases into the atmosphere, leading to a warming effect known as global warming. These activities include burning fossil fuels like coal and oil, deforestation, and industrial processes.

This global warming has far-reaching effects on the Earth’s climate systems, leading to more intense and frequent heatwaves, rising sea levels due to melting ice caps, increased frequency and severity of natural disasters like storms and wildfires, and significant disruption to ecosystems and agriculture.

What the Paris Agreement hopes to accomplish 

The Paris Agreement is an international treaty designed to address these challenges. It was adopted by 196 Parties at COP 21 in Paris on 12 December 2015 and entered into force on 4 November 2016. Its goal is to limit global warming to well below 2, preferably to 1.5 degrees Celsius, compared to pre-industrial levels.

This goal was established in response to scientific consensus that a global warming of 2 degrees Celsius would have catastrophic impacts on the planet, including severe and potentially irreversible changes to weather patterns, ecosystems, and biodiversity. 

The lower goal of 1.5 degrees was included in recognition of the fact that even 2 degrees of warming could have serious consequences, particularly for vulnerable populations such as small island nations.

How to achieve the Paris Agreements goals 

To achieve this goal, countries that are party to the Paris Agreement have made Nationally Determined Contributions (NDCs), which are their own individual commitments to reduce greenhouse gas emissions. 

The Agreement also includes provisions for monitoring, reporting, and ratcheting up these commitments over time, to ensure that the global response to climate change continues to strengthen in the coming decades.

Furthermore, the Paris Agreement acknowledges the need for global cooperation in other areas, such as climate change adaptation, financial flows, technology transfer, and capacity building. This recognizes that some countries, particularly developing nations, will require support to both reduce their emissions and cope with the impacts of climate change.

However, despite the ambitions of the Paris Agreement, current pledges under the agreement are not yet enough to limit global warming to well below 2 degrees. As such, the Agreement includes mechanisms to increase the ambition of NDCs over time. Yet, significant action is needed to meet these goals and effectively mitigate the impacts of climate change.


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