"Australia is projected to be one of the most adversely affected regions from future changes in climate in terms of reductions in agricultural production and exports," it said.

"These changes would also have significant implications for international agricultural trade."

The bureau projects that Australian exports of key farm commodities could fall by between 11 percent and 63 percent by 2030 and by between 15 percent and 79 percent by 2050, with sugar hit hardest.

Global wheat, beef, dairy and sugar production is forecast to decline by 2-6 percent by 2030 and by 5-11 percent by 2050.

Australia is the world's second-largest exporter of wheat and beef, the third-largest exporter of sugar and is one of the biggest dairy exporters.

The country's worst drought in 100 years has already decimated crops in three of the last six years, halving the biggest crop, wheat, to around 12 million tonnes this year.

The bureau projects that Australian wheat production will fall by 9.2 percent by 2030 and 13 percent by 2050.

Beef production is forecast to fall by 9.6 percent and by 19 percent over the same period; sheep meat by 8.5 and 14 percent; dairy by 9.5 and 18 percent; and sugar by 10 and 14 percent.

Australian exports of wheat are forecast to fall by 11 percent by 2030 and 15 percent by 2050.

Beef exports are forecast to fall by 29 percent by 2030 and by 33 percent by 2050; sheep meat by 15 percent and 21 percent; dairy by 19 and 27 percent; sugar by 63 and 79 percent.

Australia's exports of wheat are presently worth around A$3 billion a year and are worth A$4 billion in a good year. Beef exports are worth about A$4.5 billion a year; dairy about A$2.5 billion; and sugar about A$1.5 billion.

Agricultural productivity in Australia is forecast to fall by 17 percent by 2050.