Developing countries could be hit hard by the changing climate, but wealthy countries aren’t off the hook, a major new UN report says.

The climate change threat to the Great Barrier Reef and the Murray Darling Basin is a stark reminder that we’re not immune to the risks detailed in a major UN global warming report, Australian scientists warn.

The latest Intergovernmental Panel on Climate Change (IPCC) report says the impacts of a changing climate are already being felt across the globe, but most nations are “ill-prepared” for the worst.

Left unchecked, a warming climate would increase the likelihood of “severe and pervasive impacts” that could prove challenging to manage or be simply irreversible, the report warned.

For Australia that means an increasing risk of extreme weather conditions such as droughts and bushfires and irreparable damage to the Great Barrier Reef, which was singled out in the report.

The findings from more than 300 lead authors from 70 nations were released in Japan on Monday, and quickly saw environmental, aid and political groups urging world leaders to do more.

US Secretary of State John Kerry said the cost of inaction was “catastrophic” and warned that unless quick and dramatic steps were taken to combat climate change our way of life was “literally in jeopardy”.

Prime Minister Tony Abbott was more muted, saying the IPCC message had been clear for years and the government was committed to reducing emissions through its Direct Action plan.

“The CSIRO, amongst many other reputable scientific organisations, has cautioned against attributing any particularly weather event to man-made climate change,” he told reporters in Perth on Monday.

“Australia is a land of droughts and flooding rains, always have been, always will be.”

Labor and the Australian Greens accused the government of ignoring the climate science, while environment groups pointed to species degradation and the health risks posed by worsening heatwaves.

The IPCC said climate change was being felt everywhere regardless of a nation’s wealth, and the future bounty of the Murray Darling food bowl and Queensland’s dazzling reef could be at stake.

“Developed countries are not immune, being rich is no protection from climate change,” Associate Professor Frank Jotzo from the Australian National University said.