Global warming is more than a third to blame for a major drop in rainfall that includes a decade-long drought in Australia and a lengthy dry spell in the United States, a scientist said on Wednesday.

The forecast for Sydney in summer 2060 is hot, polluted and deadly to the elderly.

Rising summer temperatures due to global warming, drier weather and smog from transport and bushfires will make Australia's lifestyle capital a health hazard, a scientist told a major climate change conference on Wednesday.

Australia has drafted laws that mandate the generation of 20 percent renewable energy by 2020 and the government aims to have the legislation passed within months.

The Mandatory Renewable Energy Target legislation aims to expand the target under an earlier scheme to 45,000 GWh by 2020 from 9,500 gigawatt-hours (GWh) in 2010.