The smoke from Australia’s fires is so vast that fumes from the early weeks of the crisis will survive a journey around the globe and are expected to return to the country’s skies from the west, according to Nasa.
The smoke has billowed into the lower stratosphere, reaching 17.7 kilometres above sea level.
Many Australian cities and towns are struggling with low air quality from bushfire smoke. Canberra recently surpassed an Air Quality Index of 4,500 – and anything over 200 is considered hazardous.
"The smoke is expected to make at least one full circuit around the globe," Nasa, the US space agency, said.
"Once in the stratosphere, the smoke can travel thousands of miles from its source, affecting atmospheric conditions globally," it added.
On Monday night Melbourne’s air quality was the worst in the world, according to Victoria's Chief Health Officer, Brett Sutton.
More than 100 fires were still burning across Australia on Tuesday, with a number of towns and cities shrouded in smoke, but the prospect of coming rain offers a glimmer of hope.
The Bureau of Meteorology forecasts rain, possibly ranging from 30 to 80mm, across the east of Australia between Thursday and Sunday.
Mark Williams, superintendent at the New South Wales Rural Fire Service’s Shoalhaven Fire Control Centre, told The Telegraph last week that tropical storms in Australia’s north offered the prospect of rain in the south east of the country.
“A cyclone has hit the north of Australia, that could push humidity into central Australia then flow on to us,” he said. “There is no end in sight (for the fire crisis) in the absence of significant rain.”
The heavy rain will most likely fall in the mountain ranges, with isolated daily totals in excess of 50mm per day possible in some pockets.
While a welcome respite from hot and dry weather, it is unlikely that enough rain will reach the fire zones to end the long-running crisis.
Light rain would do little to stop the huge blazes, but would make it impossible to conduct controlled burns to reduce fuel loads in strategic areas. It could also, as was the case last week, make it difficult for fire fighters to manoeuvre heavy equipment.
Early on Monday, however, the NSW Rural Fire Service expressed some optimism, tweeting that if the forecasts come “to fruition… this will be all of our Christmas, birthday, engagement, anniversary, wedding and graduation presents rolled into one”.
More than 11 million hectares has been lost to the blazes this fire season, coming after the hottest and driest calendar year on record in Australia.
A recent inquiry by the Australian Broadcasting Corporation found that of the land burnt through in New South Wales this season, only about one per cent can be officially attributed to arson. In Victoria, where more than 1.25 million hectares has burned, only 385 hectares - or 0.03 per cent - have been attributed to suspicious circumstances.
The fire crisis has inspired tens of thousands of people to volunteer for bush fire fighting service. The New South Wales RFS reported 25,000 people applying to join since November, more than five times the usual number for this time of year. The Victorian and South Australian fire services reported big spikes in applications as well.
Also, since 2 January, the Tradies for Fire Affected Communities group on Facebook has recruited more than 9,000 members who are tradespeople offering to work for free on fire recovery and reconstruction projects.
And a bushfire relief concert featuring Alice Cooper, Queen, Olivia Newton-John and many other artists has sold out within 24 hours.
More than 70,000 people are expected to attend the benefit concert in Sydney next month.
Organisers of the Fire Fight Australia concert said the response is a “heart-warming display of unity and solidarity during times of national hardship”.