The researchers studied how the Hadley Circulation – the movement of warm air and moisture away from the tropics – will be affected if carbon-dioxide emissions continue to rise at the rate of 1 per cent per year.

They found evidence of a so-called "deep-tropics squeeze", in which regions closest to the equator will experience increased convection as air rises faster.

Conversely, the drier sub-tropical regions characterised by descending air and resulting high-pressure systems will expand, according to the research published Tuesday in the Proceedings of the National Academy of Sciences.

"Our results provide a physical basis for inferring that greenhouse warming is likey to contribute to the observed prolonged droughts worldwide in recent decades," the paper said.

Existing dry zones in Africa-Eurasia, south-west North America and much of Australia will face increased risk of drought, said William K.M. Lau, of the University of Maryland's Earth System Science Interdisciplinary Centre, and co-author of the paper.

"As inferred from the model projections, the global warming effect on expansion of deserts is likely to be already going on," Dr Lau told Fairfax Media.

The paper found that while some components of the Hadley Circulation will strengthen – resulting in increased rainfall in the deep tropics – ther elements will weaken. These findings will aid the understanding of the overall changes under way, he said.

"Detection of changes in the Hadley Circulation has been attempted by many previous authors, with no clear results whether it has strengthened, weakened or [had] no change," he said.

Steve Turton, a climatologist at James Cook University, said the PNAS paper adds to other research indicating the tropical belt is expanding, such as signs that the location of the maximum intensity of cyclone is shifting poleward.

An intensification of deep tropical rainfall would mean more rainfall for regions to the north of Australia, such as Indonesia, Professor Turton said.

A further expansion of the high-pressure belt, on the other hand, means more rainfall missing mainland Australia, and falling in the Southern Ocean instead. "It spells a pretty grim forecast for Australia," he said.

Rainfall is already on the decrease in southern Australia. Important winter rains over south-western WA have reduced by about a quarter since the 1970s, adding stresses to ecosystems and raising doubts about the prospects for wheat farming in the region, Professor Turton said.

Other regions reliant on monsoonal rains, such as the Indian sub-continent, will also likely see a disruption of rainfall patterns, he said.