Bushfire smoke to return to Australia after full circuit of the globe

NASA says smoke from Australia's devastating bushfires will pass back over the country after travelling around the globe.

But the high concentration of carbon dioxide may continue on, with the space agency warning the smoke will make "at least one full circuit".

The smoke has already reached South America, resulting in hazy skies over Chile and Argentina.

But at its current trajectory, it will also pass over the Atlantic, Africa and the Indian ocean before returning to Australia.

Which means Perth could find themselves in hazy conditions within the week. The state has been spared the worst of the bushfires.

NASA imagery shows the full extent of the smoke cloud, using a "UV aerosol" index.

"The UV index has a characteristic that is particularly well suited for identifying and tracking smoke from pyroCb (pyrocumulonimbus) events: the higher the smoke plume, the larger the aerosol index value," NASA research scientist Colin Seftor said.

"The aerosol index values produced by some of the Australian pyroCb events have rivalled that largest values ever recorded."

But much of the smoke from the bushfires has lingered over the continent.

Melbourne has the worst air pollution in the world thanks to the bushfires, an ignominious crown taken from Canberra last week.

And Sydney has faced more than a month of smoke haze, some days much heavier than others.