Australia must drastically increase its emissions reduction target to 40% by 2020 to avoid “almost unimaginable social, economic and ecological consequences” from climate change, a new book penned by leading scientists and economists, including Ross Garnaut, has warned.

The book, Four Degrees of Global Warming: Australia in a Hot World, sets out a series of stark scenarios facing the country should global temperatures rise by 4C above the pre-industrial average.

By 2100, annual rainfall in southern Australia is likely to fall by 50%, the sea level is set to rise by 1.1m and snow cover will fall “to zero in most alpine regions”, the book warns.

With temperatures rising by 3-5C in coastal areas and 4-6C in inland areas, Australia’s future will be a “disturbing and bleak vision of a continent under assault”, according to the book, which was compiled following two years of original research by its authors.

Dramatic climatic shifts will give Sydney the current day climate of Rockhampton, while Melbourne will become similar to Griffith in NSW. More exotically, the climate of Alice Springs will become comparable to that of the Sudan, while Darwin may become “in terms of climatic extremes, unlike anywhere currently on the planet”.

The Great Barrier Reef will “decline precipitously” with 4C of warming, common species will become endangered or extinct, and production in the key Murray-Darling food bowl could slump by 90%, leading to food insecurity.

Heat-related deaths are predicted to triple to 17,200 from 1990 levels, with Sydney set to experience 12 days a year over 35C by 2070. Melbourne will endure 26 days above this temperature mark, while Perth is due to swelter for 67 days a year above 35C.

Economically, Australia is set to experience “shocks and hard times” from climate change, according to a chapter penned by Garnaut. A 4C warmer Australia is expected to put severe strain on the tourism industry and the welfare state.

The premise of the book is what its editors consider to be the most likely warming scenario facing the world without further radical action. Authors include Garnaut, who analysed the impact of climate change under the first Kevin Rudd government, and climate scientists including David Karoly, Kevin Hennessy and Will Steffen.

The IPCC has several different models for future temperature rises, ranging from 1.5C to nearly 6C. Four Degrees of Global Warming editor Peter Christoff, associate professor of environmental policy at the University of Melbourne, said even if current carbon emissions reduction pledges were enacted by major economies, the world is on track to 4C warming by 2100 – a position also expressed by the World Bank.

Although nations have committed to limit warming to below 2C, the book calculates that the world emits far too much CO2 – to the tune of 14bn tonnes – to keep to this target. For this gap to be bridged, Australia would have to raise its emissions reduction target to 40% by 2020 in order to do its fair share, based on current emissions levels. This is well above its current target of a 5% cut based on 2000 levels.

Christoff told Guardian Australia that the scenario for Australia was “extraordinarily disturbing and deeply distressing” if average temperatures increased by 4C.

“Australia is exceptionally vulnerable ecologically to climate change,” he said. “It would mean a comprehensive transformation for life in Australia, from its wealth to its access to water to how people spend their time in summer.

“We’re looking at a significant wave of extinctions and the almost certain devastation of the Great Barrier Reef. We’ll see critical parts of the economy, such as the mining sector and tourism, falter, which is likely to lead to a society which is poorer and with a greater differential of wealth.”

The Coalition has vowed to scrap the carbon price mechanism and replace it with its Direct Action policy, offering financial incentives to businesses to reduce emissions. Several independent studies have showed that the $3.2bn allocated under Direct Action will not be sufficient and that the 5% emissions reduction target will not be reached.

Christoff said the 5% target was “socially and environmentally irresponsible”, and that a 40% cut was required. This goes beyond the 15% to 25% the Climate Change Authority postulated in October when it called the 5% target “not a credible option”.

“Everything that has been done economically in this space, by Ross Garnaut or Lord Stern, shows that going hard earlier is cheaper and more effective, even if other countries delay,” said Christoff. “The current effort is vastly inadequate for the problem.

“It seems the current government is not interested in carbon pricing, instead preferring a voluntary and economically expensive option. Australia is going from a country that was showing some progress on climate change to one that’s in fast reverse.”

The report echoes dire predictions outlined by a leaked IPCC draft that shows Australia is set to experience a 6C temperature increase on its hottest days and the loss of the Kakadu wetlands due to climate change.