Climate change is claiming millions of lives annually through extreme heat, air pollution, wildfires and the spread of deadly infectious diseases, according to the most comprehensive assessment to date of the links between climate change and health.

The ninth annual Lancet Countdown report, authored by 128 experts from 71 academic institutions and UN agencies worldwide, reveals that 13 of 20 indicators tracking health risks and impacts from climate change reached concerning new records in the latest year for which data is available.

The findings arrive as the world exceeded 1.5°C above pre-industrial temperatures for the first time in 2024. Greenhouse gas emissions rose to record levels as the lack of a global response to climate change sets the world on track for a catastrophic 2.7°C to 3.7°C of warming by the end of the century.

“We’re really worried, to be very honest with you. We’re really, really worried from the scientific perspective, because we have the data,” said Marina Romanello, executive director of the Lancet Countdown at University College London, describing this year’s report as “a bleak and undeniable picture of the devastating health harms reaching all corners of the world.”

“There’s no denying how the situation is, how policies and actions are not going in line with what the evidence shows,” Romanello said. “We’re seeing millions of deaths that are occurring needlessly every year because of our persistent fossil fuel dependence, because of our delay in mitigating climate change, and our delays in adaptation to the climate change that cannot be avoided.”

The Lancet findings add to the chorus of urgency surrounding the upcoming climate summit, COP30, in the Brazilian Amazon city of Belém. As the world drags its feet, science indicates the original call of the Paris agreement to limit warming to 1.5°C is already dead.

“Let’s recognise our failure,” UN Secretary-General António Guterres told the Guardian this week. “The truth is that we have failed to avoid an overshooting above 1.5°C in the next few years.”

Without immediate course correction, the mounting death toll documented in the Lancet report represents only the beginning of a health catastrophe that will claim tens of millions more lives as temperatures continue to rise.

“Overshooting is now inevitable,” the UN chief said. “Going above 1.5°C has devastating consequences.”

Overheat

As the planet warms, human health is caught in the crossfire. Heat exposure claimed an estimated 546,000 lives annually in the most recent decade of data, marking the first time researchers have quantified the absolute mortality toll from rising temperatures. 

On average, 84% of the heatwave days that people experienced between 2020 and 2024 would not have occurred without climate change.

“That’s approximately one heat-related death every minute of the year,” said Ollie Jay, professor of heat and health at the University of Sydney and co-chair of the report’s first working group.

Jay warned of approaching physiological limits beyond which human survival becomes impossible. 

“One of the things that we’re really worried about in the heat and health space is reaching these physiological tipping points where combined temperature and humidity that people are presented are actually not survivable for a given level of exposure time, and we’re reaching, potentially reaching, these limits in different parts of the world at an alarming rate,” he said.

Jay’s concern aligns with other independent projections. Modelling published in the Proceedings of the National Academy of Sciences found the planet could see a greater temperature rise in the next 50 years than in the previous 6,000. 

Extreme heat zones like the Sahara – now covering less than 1% of land on earth – could expand to nearly 20%, potentially pushing one in three people on the planet outside the climate niche humans have lived in for millennia. 

Emerging data suggest these physiological tipping points are “actually cooler and drier than we previously thought,” Jay noted, meaning vast regions could become uninhabitable far sooner than anticipated.

With heat comes drought. Extreme drought affected a record 61% of global land area in 2024, which is 299% above the 1950s average, threatening food and water security. 

The higher number of heatwave days and drought months in 2023 was associated with 123.7 million more people experiencing moderate or severe food insecurity across 124 countries analysed, compared with 1981-2010, the report found. 

The economic toll is escalating in parallel. Weather-related extreme events in 2024 caused $304 billion in global economic losses, a 59% increase from the 2010-14 annual average.

Heat exposure resulted in 639 billion potential work hours lost in 2024, totalling $1.09 trillion in potential losses— almost 1% of the global economy.

For countries with low human development indices, the losses approached 6% of GDP, undermining the economic foundations on which health systems depend. 

“Around the world we are seeing these multiple health impacts compound each other to trigger a cascade of harms that undermine the very social and economic foundations taht support people’s health,” said report co-author Stella Hartinger,

“It’s clear that these health harms are the price we are paying for the consistent failure of global leaders to deliver the action needed to combat climate change and protect health–a price paid most severely by vulnerable countries that have contributed the least to the crisis.”

Fire and Smoke 

The report attributes 2.52 million deaths in 2022 to outdoor air pollution from fossil fuel combustion, with the transport sector the biggest single contributor globally from petrol use. 

Household use of dirty fuels and technologies across 65 countries resulted in 2.3 million deaths in 2022, deaths that could be avoided through transitioning to clean renewable energy.

“The evidence could not be clearer. Climate change is taking a horrific toll on people’s health worldwide, on top of the millions of preventable deaths every year from air pollution,” said Nina Renshaw, head of health at the Clean Air Fund.

Wildfire smoke claimed a record 154,000 lives in 2024, a 36% increase from baseline years. Research increasingly shows wildfire smoke is more toxic than typical air pollution due to its high black carbon content, with emerging links to dementia and other long-term health impacts.

“2024 saw record deaths from air pollution from wildfires driven by climate change, showing the urgency of curbing emissions to stop this insane death spiral,” Renshaw said. “Action on super pollutants, like black carbon and ground-level ozone, is our emergency brake to decisively slow global warming.”

Mosquitoes on the move

The changing climate is also expanding the geographic range where deadly infectious diseases can spread, the Lancet report found.

The transmission potential for dengue by its two main mosquito vectors increased by 48.5% and 11.6% respectively from 1951-60 to 2015-24, contributing to the 7.6 million dengue cases reported globally in early 2024.

“Finding mosquitoes in Iceland cannot be good news,” Romanello said, referring to recent detections linked to rising temperatures. 

The appearance of disease-carrying mosquitoes near the Arctic Circle is the tip of a rapidly warming iceberg reshaping the geographic boundaries of vector-borne diseases, potentially exposing millions of previously protected populations to infections like malaria, dengue and Zika for the first time.

“The health threats of climate change, once again, are breaking new records,” Romanello said. “They broke records the year before, and they set new record this year.”

“What worries us most is not just a single indicator, a single threat increasing, but that all these threats are increasing in parallel, and they often compound each other.”

Political will evaporates as crisis deepens

The global response is moving in the wrong direction even as health impacts accelerate. The report found that 12 of 20 indicators monitoring climate and health action worsened in the latest year of data, with six showing reversal of previous progress.

Mentions of health and climate change by governments in their annual UN General Assembly statements declined from 62% in 2021 to 30% in 2024.

“If we remain locked into fossil fuel dependence, health systems, cooling infrastructure, and disaster response capacities will soon be overwhelmed, putting the health and lives of the world’s 8 billion people further at risk,” said Nadia Ameli, Lancet Countdown working group 4 co-chair. “Each unit of greenhouse gases emitted drives up the costs and challenges of adaptation.”

The engagement that remains is mostly driven by countries least responsible for but most affected by climate change, while engagement is falling among some of the world’s greatest greenhouse gas emitters and the private sector.

The 100 largest oil and gas companies have production strategies that put them on track to exceed their share of production consistent with 1.5°C of heating by 189% in 2040, up from 183% in March 2024, the Commission found.

Private bank lending to fossil fuel sector activities surged 29% to $611 billion in 2024, exceeding green sector lending by 15%. Some 73 of 87 countries reviewed provided net explicit fossil fuel subsidies in 2023, allocating nearly $1 trillion in direct support.

Including indirect subsidies, that figure rises to over $7 trillion, according to the International Monetary Fund — more than governments spend annually on education and about two-thirds of what they spend on healthcare.

Fifteen countries allocated more funds to net fossil fuel subsidies than to national health budgets, according to the report.

“If we keep on enabling this expansion of fossil fuels, we know that a healthy future is not possible and that all of these environmental determinants of health will get much worse very, very fast,” Romanello said. “The destruction to lives and livelihoods will continue to escalate until we end our fossil fuel addiction.”

World heading for catastrophic warming

The backsliding documented in the Lancet report means the health impacts breaking records today will only intensify as the world continues to burn.

The analysis of nationally determined contributions from the 64 countries that have submitted updated pledges shows projected emissions in 2035 are only 10.2% below 2019 levels, far short of the 60% reduction needed to limit warming to 1.5°C, according to a synthesis report released Tuesday by the UN Framework Convention on Climate Change.

“The scale and severity of the climate crisis has never been clearer,” said Simon Stiell, UNFCCC executive secretary. “Brutal climate-driven droughts, floods, storms and wildfires are hitting every nation harder each year, wrecking millions of lives and gutting national budgets.”

“This wider picture, though still incomplete, shows global emissions falling by around 10% by 2035.”

That figure, however, includes commitments from the United States under the Biden administration. In January, President Donald Trump told the UN General Assembly that climate change was “the greatest con job ever perpetrated on the world, in my opinion.”

“If you don’t get away from this green scam, your country is going to fail,” Trump said, dismissing decades of scientific research. 

“All of these predictions made by the United Nations and many others, often for bad reasons, were wrong. They were made by stupid people that have cost their countries fortunes and given those same countries no chance for success.”

“It’s nonsense,” the US President said. “I’ve been right about everything.”

With the US commitment now void, the actual projected emissions reduction falls to approximately 6%, making the gap to 1.5°C even wider. 

“The road we have to travel between today and 1.5 is incredibly steep,” Guterres said in the Guardian interview, urging nations to “change course now.” 

The world’s other largest emitter, China, has been roundly criticized by scientists and experts for continuing to increase its emissions, which surpassed the total historical emissions of Europe last year.

“We already have the solutions at hand to avoid a climate catastrophe,” Romanello said. “Rapidly phasing out fossil fuels remains the most powerful lever to slow climate change and protect lives. Shifting to healthier, climate-friendly diets and more sustainable agricultural systems would massively cut pollution, greenhouse gases and deforestation, potentially saving over ten million lives a year.”

Missing trillions

The UNFCCC synthesis found that 88% of countries included unconditional elements in their climate pledges, while 67% included more ambitious conditional elements dependent on access to enhanced financial resources and technology transfer. 

These conditional targets mean that many countries, especially poorer nations in the path of climate destruction, will only implement more aggressive emissions cuts if wealthier countries provide the climate finance needed to support the transition.

A total of 52% of countries reported climate finance needs in the range of $1.97 trillion to $1.98 trillion, comprising $1.07 trillion to $1.08 trillion identified as support needed from international sources.

“An equitable global transition, where every country benefits from clean energy and climate resilience, requires clear policies and plans, across every country and every sector, and more support for many nations, especially those that did least to cause this global crisis,” Stiell said.

Negotiators agreed to a new collective quantified goal of only $300 billion by 2035 at COP29 in Baku, less than a third of the identified need and payable over a decade rather than immediately. 

The least developed nations called the figure a “betrayal,” noting that amount won’t be reached for decades, when the impacts of climate change and needs are far more severe and expensive.

“The poorest countries in the world are already spending more on debt service than on healthcare, education, and infrastructure combined,” said Jess Beagley, policy lead at the Global Climate and Health Alliance.

“It’s clearer than ever that the level of finance agreed to in the new goal is insufficient to deal with the devastating health consequences of climate change,” she added. “Continuing to raise ambition is a matter of life and death.”

Some countries allocate over 80% of government revenue to debt servicing, leaving only 20% for social services and development.

Yet international climate finance comes predominantly as loans rather than grants, creating a vicious cycle where countries need finance to implement climate action but lack the fiscal space to take on more debt, while climate impacts further erode their economic capacity. 

The debt trap leaves health systems chronically underfunded and unable to cope with rising climate-related disease burdens, heat casualties and disaster response needs.

“A political shift towards reduced foreign aid support from some of the world’s wealthiest countries further restricts financial support for climate change action, leaving all populations increasingly unprotected,” Romanello said. “There is no time left for further delay.”

Image Credits: Mike Newbry/ Unsplash.