We all know the feeling of a hot, sticky day - when the air is heavy, your clothes cling, and even sitting still feels tiring. Shade doesn’t cool you, a breeze barely helps, and it’s hard to get much done.
But at certain combinations of heat and humidity, the discomfort becomes a threat to your life.
Lethal humidity is one of the most urgent and least recognised climate threats of our time. It happens when extreme heat and high humidity combine to push the human body beyond its limits. It is already affecting lives and livelihoods.
These days used to be rare. Now, they’re happening more often.
Across the world, rising humidity combined with heat is making everyday life more challenging.
It’s not just about discomfort - it affects how we work, how we rest, and how communities plan for the future. What was once seen as an inconvenience is now emerging as a serious issue for wellbeing, livelihoods and public safety.
Minderoo Foundation and the Lethal Humidity Global Council (LHGC) are drawing attention to how this threat is shaping health, jobs, migration and security, and how experts are working on solutions.
Here are five things you should know about lethal humidity.
1. It’s changing how we cope with heat.
On a dry summer day, we can usually sweat our way through the worst of it. But when humidity is high, this process stops working and that’s when heat turns from uncomfortable to dangerous.
In dry heat, the human body can survive temperatures up to about 54°C. But when humidity is high, sweating no longer cools us, meaning heat stroke can occur at just 30–35°C.
For every degree the planet warms, humidity rises by about 7 per cent. This means more regions are entering dangerous conditions, especially in the tropics and subtropics. Babies, older people, outdoor workers and those with health issues are most at risk.
In Australia, the effects are becoming more visible. Scientists use a measure called wet-bulb temperature to assess heat stress on the body.
At high levels, it becomes impossible to cool down, even in the shade.
In 2023, the Australian women’s soccer league postponed matches because conditions reached unsafe levels. Farmers are reporting heat stress in livestock. Households are seeing rising insurance premiums after record heatwaves and floods drive up the cost of claims.
Similar extreme heat events are now being recorded in the United States and United Kingdom, where high humidity has made already dangerous conditions even harder to cope with.
2. It amplifies everyday pressures.
Lethal humidity does not just reflect climate change, it makes the risks worse. When heat and humidity rise together, people can no longer safely work or live in affected areas.
The impacts are wide-reaching: working hours are lost, food production and supply chains are disrupted. Communities are displaced, health systems come under pressure and costs rise. Security and stability are affected.
At its core, lethal humidity is about disruption to people’s lives – health, jobs, mobility, food on the table and the stability of communities.
3. Experts are coming together to find solutions.
Communities, researchers and policymakers are recognising that humid heat isn’t just another climate problem – it’s one of the defining challenges of our time. The good news: collaboration is growing fast.
Lethal humidity is increasingly recognised in science, policy and media as a critical issue and is fast becoming one of the defining climate challenges of this century.
In 2023, Minderoo Foundation and partners helped establish the Lethal Humidity Global Council. It now has more than 160 members in nine countries, including leading universities, research groups, governments, charities and businesses. This network brings together expertise across climate science, health, technology and policy, creating a global hub for urgent action.
4. Research is showing us the bigger picture.
From understanding how older people cope with humid heat, to measuring impacts on livestock and crops, new research is giving us the data we need to prepare and adapt.
Members of the LHGC are building the evidence base on how lethal humidity affects people, economies and ecosystems. This includes studies on health, food security, livestock and gendered impacts.
Researchers are also exploring how extreme humidity in the Global South can be linked to human-driven climate change. Others are building improved climate models to forecast dangerous events.
This evidence is strengthening global awareness and making the case for urgent action.
5. New tools are helping communities prepare.
Solutions are already taking shape. Early warning systems, better climate models, and practical advice for farmers are giving people the chance to plan ahead – and in many cases, save lives.
Minderoo-funded research will play a critical role in tackling this issue. A global early warning system for humid heatwaves is being developed using machine learning and seasonal forecasting. This will forecast when and where conditions are likely to become dangerous, giving governments and communities time to act and save lives.
Other projects are mapping how livestock and crops respond to humid heat, setting heat stress limits for different species, and feeding this into climate models. These insights will help farmers plan, safeguard food supplies and protect rural incomes.
These tools are critical, but they only buy us time. The root driver of lethal humidity is greenhouse gas emissions from burning fossil fuels.
As long as emissions continue to rise, humid heat will become more frequent and more severe – outpacing even the best warning systems and adaptation strategies.
Minderoo Foundation is proud to support the LHGC and its mission to make lethal humidity part of the global climate agenda.
But preparedness alone is not enough – the only way to prevent this threat from worsening is to tackle its cause: the extraction and burning of fossil fuels.
That’s why we must achieve Real Zero – the complete elimination of greenhouse gas emissions from fossil fuels. Real Zero is the only path that can reliably limit warming within the Paris Agreement’s guardrails, and the only path that can reduce the risks of lethal humidity for generations to come.