Thousands of Australians have rallied in support of a government plan to impose a tax on carbon emissions, which have been blamed for global warming.

Demonstrators in major cities across the nation carried signs Sunday and shouted slogans saying yes to carbon tax. June fifth is United Nations – designated World Environment Day.

Environmental activists and some celebrities spoke of the duty to ensure future generations against climate change. Oscar-winning actress Cate Blanchett joined the rally in Sydney.

Australia relies heavily on coal-fired power and is one of the world's worst polluters. A carbon-emissions tax is the subject of heated debate in the country. Prime Minister Julia Gillard ruled out the tax during her election campaign, but earlier this year she proposed a fixed-price levy on major carbon polluters to start in July of 2012.

Big businesses, especially the country's powerful mining industry, have urged the government to set a low starting price of about $10 per ton for carbon emissions, saying that anything more than that would be harmful to Australia's economy.

The conservative opposition has criticized the government's proposal in parliament.

The government last week released a new report warning of the potentially harmful impact of rising sea levels on the ecosystem in Australia's beloved Kakadu wetlands on the northern coast. The World-heritage listed site has been the home of the indigenous Bininj people for some 60,000 years.