Heatwaves are becoming longer, hotter and more frequent as a result of climate change. There is no where for us to hide, and thinking that we can simply "toughen up" or that air-conditioning will come to the rescue is folly, writes Dr Liz Hanna.

Heat records are falling like skittles - they don't last for long anymore.

2014 had been the world's hottest year since records began in 1880, but it held that title for only one year, as today 2015 was confirmed as being even hotter by a significant measure.

This is particularly bad news for the health of all Australians, even the young, fit and resilient.

Let me explain why. Global warming is accelerating, in line with increasing greenhouse gas emissions, and in 2015 this was boosted by a big el Nino event.

This is a world problem but one that is especially worrying for Australia, which is actually tracking ahead of this curve. Globally, the combined average land and ocean annual temperature for 1901-2000 was 13.9C, and the annually averaged temperature over land for the same period was 8.5C.

Compare that to Australia's average air temperature over land (1961–1990) of 21.8C. Admittedly, these time scales do not mirror each other, but the difference of 13.3C is significant and highlights how far Australia is ahead of the global average in terms of exposure to heat.

Most of us are feeling the heat. Sydney, Melbourne, Adelaide and Perth - all highly populous major cities - have all experienced temperatures over 45C, and for inland regions it's closer to 50C. All around our country there are more record hot days, and record hot months. Heatwaves are becoming longer, hotter and more frequent. In short, there is no where for us to hide.

It is pure folly to think that air-conditioning is our saviour. To fully function as a society, Australians must venture outside. Commuting, shopping, tending to domestic needs, caring for others, accessing essential services, and even working involves exposure to the ambient climate. Many of these vital activities cannot be delayed or postponed.

Imagine the scenario when repeated heatwaves emerge, when walking to the bus is hazardous, and such situations linger for weeks throughout summer. Some might say we just need to toughen up. But the fact is there are physiological limits to human's capacity to remain active in the heat.

The ambient temperature for optimal human physical performance is about 11C. Temperatures in excess of that progressively degrade transfer of the additional heat generated by movement to the environment, and core temperatures rise. Fatigue is a self-protecting response to limit heat generation. Persistent exercise in high temperatures results in dangerously high core temperatures and heat stress, which can ultimately be fatal.

Yes, you can adjust to heat over time and achieving a stage of acclimatisation does provide some protection. However, this process is complex, and takes several weeks of prolonged physical activity in the heat to achieve. The process of acclimatisation itself is also risky. Furthermore, acclimatisation erodes in the absence of regular heat exposure.

Early season heatwaves are particularly dangerous in this regard. Intermittent heat exposure is therefore also hazardous, which places fly-in-fly-out workers at high risk.

Acclimatisation also dips when the body is stressed for other reasons, such as mild infections. The consequence is that every member of society is at risk of heat stress on hot days, and especially so on days of extreme heat.

In order for such risks to be managed effectively, we must be aware of them, understand them and factor these risks into our daily lives. Australians still underestimate the hazardous nature of heat to our health, as many still regard it as a problem only for the elderly, and very young. Few realise that it's not just school children but those who are fit and aged in their 20s, 30s and 40s who all appear in heat mortality statistics.

My own recently completed study examining heat exposure in the Australian workforce identified an over assessment of heat tolerance. This study recruited people who routinely work in hot environments. They are well-acclimatised and accustomed to functioning and moderating their heat exposure. Early symptoms of heat stress regularly occurred at temperatures they had previously listed as safe to keep working. This highlights a potentially dangerous lack of recognition of heat as a personal health risk.

All Australians are therefore vulnerable to heat. The young and fit are not excluded from risk of heat death, and a change of attitude towards heat is urgently required. We also need to interrupt the process of further warming before our nation is exposed to massive heat death events.

Dr Liz Hanna is the director of the Working in the Heat program at the Australian National University. Dr Hanna is also president of the Climate and Health Alliance.