The health harms caused by climate change have escalated over the past decade, with heat linked to a record 710,000 deaths globally in 2023, according to a major international report involving seven University of Sydney researchers. 

The 2026 Report of the Lancet Countdown on Health and Climate Change found that many climate-related health risks grew faster in the decade after the Paris Agreement was introduced than during the previous decade. 

Professor Ollie Jay, Director of the University of Sydney Heat and Health Research Centre and Chair of the report’s Working Group 1, said: “The evidence is now unequivocal that climate change is harming health in every region of the world.

“Our indicators show people facing more days of dangerous heat, greater exposure to extreme weather, and growing threats from food insecurity and infectious disease. These are measured impacts on people’s lives today, and they are accelerating.”

The 10^th annual indicator report represents the work of 146 researchers from 71 institutions and monitors 54 indicators covering the health impacts of climate change and the effects of climate action. It was led by University College London in strategic collaboration with the World Health Organisation. 

“Tracking these impacts year on year gives governments and those with policy-making responsibility the evidence they need to act, and to know whether their actions are working,” Professor Jay said.

The seven University of Sydney authors of this year’s report include Associate Professor Ying Zhang from the Sydney School of Public Health, and six members of the Heat and Health Research Centre: Professor Ollie Jay, Dr James Smallcombe, Dr Jake Williams, Dr Philomena Colagiuri, Dr Federico Tartarini and Dr Troy Cross. Collectively, the Heat and Health Research Centre has the second-highest number of author affiliations in the report. 

Heat was associated with an average of 540,800 estimated deaths per year between 2016 and 2023. Climate change was responsible for an estimated 369,900, or 68 percent, of those deaths. 

In 2023 – the hottest year in that period – heat was linked to a record 710,000 deaths globally. More than 70 percent of that toll was attributable to human-caused climate change. Across 2016 to 2023, climate change is estimated to have caused almost 3 million heat-related deaths.

Heat exposure also reduced people’s capacity to work, resulting in an estimated 573 billion potential work hours lost in 2025 and US$1.07 trillion in potential income losses. 

South-East Asia and Africa were hit the hardest, with estimated losses equivalent to 3.9 percent and 3.2 percent of GDP, respectively. 

The report also found that extreme drought affected 51.8 percent of the world’s land for at least one month in 2025, the second highest level recorded. 

A new satellite-based analysis found that, since 2003, 43 percent of global land had experienced a long-term decline in water storage, while 37 percent had experienced a long-term increase. Together, these shifting patterns affected more than 80 percent of the world’s land, with implications for food supplies and sanitation.