Australia’s spring is starting to heat up, with experienced across the country since the start of November.
Earlier this week, heatwaves swept across Western Australia, the Northern Territory, Queensland and far northern NSW.
On Tuesday, temperatures in Birdsville in western Queensland climbed to 45C and temperatures hovered above 40C in parts of south-west Queensland on Wednesday.
Victoria issued its first total fire ban of the season and a total fire ban was in force in Sydney on Friday.
The rises in heat have also brought some muggy days, with northern Australia experiencing extreme humidity.
On Thursday, the dew point temperature peaked at 25.1C in Darwin.
The dew point is the temperature to which air must be cooled in order to produce condensation, and it represents how much moisture is in the air. The higher the dew point, the greater the amount of moisture in the atmosphere.
According to the Bureau of Meteorology (BoM), a dew point temperature anywhere above 24C is “oppressive, uncomfortable for most” and can cause heat stress issues.
Sydney has also experienced some sticky days — the dew point peaked at 21.3C on Thursday — a range described by the BoM as “muggy” and “quite uncomfortable”.
Dew point days over 20C can be expected to become more common in Sydney and other parts of south-eastern Australia in the coming months.
Professor Steven Sherwood, an atmospheric sciences researcher from the University of New South Wales, told SBS News humidity is more uncomfortable than dry heat due to the way the body’s natural air conditioning system, perspiration, works.
“It only works if the water can evaporate the the more humidity there is near, the less it works. It’s also true for air conditioners, they have to work harder in humid weather — but you don’t notice because they’re just doing the work for you.”
How humid will this summer be?
Humidity is caused by high ocean temperatures. When more water evaporates, the moisture is held in the air and hot air can hold more moisture.
Dr Martin Jucker, a senior lecturer from the Climate Change Research Centre at the University of New South Wales, told SBS News that summer can be expected to be warmer than usual as the world has hit 1.5C above pre-industrial temperatures.
As for humidity, Jucker said it is unclear whether this summer will be muggier as humidity is “one of the most difficult things to predict”.
While higher ocean temperatures can drive humidity, the amount of humidity we feel on land is driven by a number of factors, including winds.
Jucker said winds blowing humid air from the ocean to the shore will increase humidity, but winds blowing away from the shore will create drier conditions.
Levels of humidity are also affected by , as well as conditions in sea ice in Antarctica and storms in specific regions.
“That makes it really, really complicated,” Jucker said.
Jucker said the difficulty of predicting humidity trends is unfortunate, given its importance.
“I realise it’s one of the most important questions because, for human health, for how many mosquitoes there are which carry diseases, all of that is based on humidity, and we’d love to predict it better, but it’s just very, very difficult.”
Is Australia’s climate getting muggier?
The summer of 2023-2024 brought record-high humidity to the east coast of Australia as the temperature of the sea surface was 1 to 3C above average.
On 11 January, Sydney registered its highest dew point on record of 26.7C — an average dew point for the time of day and date was 17C.
Global warming is creating higher ocean temperatures and the amount of water vapour over oceans has increased by around 5 per cent since the beginning of the industrial era.
Sherwood said while average humidity seems to be stable in Australia, he believes that most humid days have become more humid and dry days have become drier.
“That’s because temperatures are rising in the tropical oceans there’s more humidity there — and so when that air comes, it brings more water vapour than it used to.”
