A hot air mass parked over central Australia is delivering the second brutal heat wave this month. January is quickly approaching a record-breaking month Down Under.

These heat waves are being driven by warmer ocean temperatures, in turn heating-up central Australia and spilling across the eastern half of the continent.

"The heat waves were likely driven by warmer sea temperatures combining with the unusual spread of a 'reservoir of hot air' that had been building in central Australia over the past several weeks," said Phil King of the Bureau of Meteorology.

The Tuesday overnight temperature for Sydney, New South Wales (NSW), a city of 4.3 million people, registered 77F. By 6 a.m. the mercury read 88F and later in the afternoon, in the western suburbs, it reached a scorching 109F.

It was the hottest sticky night in five years. Thousands of people appeared at Sydney's Bondi Beach just after sunrise to cool off.

"We're not used to seeing that many people, normally it's crickets [this early in the morning] ... but there's a lot of people in the water, it makes it difficult to see them with the sun glaring in our face," said Bondi lifeguard Andrew Reid.

Along with stifling heat, the levels of smog in Sydney are very high. This prompted the NSW Health agency to issue a warning for people with respiratory conditions like asthma. High temperatures exacerbate toxic ozone created by automobiles.

"When it's really hot and quite still, we can get a built up of some pollutants, and in this case it's ozone," said David Berry, Bureau of Meteorology forecaster. "It's from the burning of fuels and having lots of air-cons on and that sort of thing."

The latest heat wave created an extreme fire emergency elsewhere in NSW and into the Australian Capital Territory near the nation's capital city, Canberra. A fast moving wildfire charred 5,500 acres of eucalypt forests.

While temperatures are beginning to relax in Sydney, the deadly heat wave is moving north into the state of Queensland and its capital city of Brisbane with 2.1 million people.

Last week, a vicious heat wave claimed the life of Matthew Hall, a fit and healthy 30-year-old man, while dirt bike riding along the Sunshine Coast.

"People need to be really aware that heat can affect especially the elderly and young children, but [also] people with previous medical conditions can really suffer a great deal," paramedic Lara King said. "Also young healthy fit people who don't think they have got any concerns need to be really cautious."

Last week, 200 other Queenslanders were treated for heat stroke and dehydration.

Two key findings on heat waves from Australia's Climate Council report Silent Killer highlighted that:

• Heat waves are a silent killer. Major heatwaves have caused more deaths since 1890 than wildfires, cyclones (hurricanes), earthquakes, floods and severe storms combined.

• Extreme heat increases the risk of heat illness and can also exacerbate pre-existing illnesses such as heart and kidney conditions. Children, the elderly, the disabled and outdoor workers are among those most at risk.

In addition to fierce heat waves, new research from the ARC Centre of Excellence for Climate System Science warned that as Earth's temperatures approach 2C, the upper limit of the Paris climate agreement, Australia will see an 11.3-30 percent intensification of rainfall from extreme precipitation events, while some areas will increase in drought.

"There is no chance that rainfall in Australia will remain the same as the climate warms," said Professor Steve Sherwood, an author of the research from University of New South Wales.

Another report, The Heat Matches On, warned that "as Australians continue to suffer from more frequent and worsening extreme heat events, the path to tackling climate change is becoming more urgent: no new coal mines can be built, existing coal mines and coal-fired power stations must be phased out and renewable energy must be scaled up rapidly."