A leading international climate change economist has urged Tony Abbott not to “wish away” the evidence for climate change or prevent it from being discussed at the upcoming G20 summit because of “local politics” and a “lack of courage” to confront the scientific evidence.

His comments come as the Intergovernmental Panel on Climate Change [IPCC] release the most rigorous synthesis of climate change science to date, making it clear that without urgent cuts in greenhouse gas emissions, global temperatures will rise by more than 2 degrees.

In a commentary for the Guardian, Nicholas Stern, chair of the Grantham Research Institute on Climate Change in the UK and a former World Bank chief economist, wrote that climate change action by politicians was now urgent, with lives and livelihoods at risk.

“With each successive decade being warmer than the last globally, and this year shaping up to be the hottest ever recorded, the reality of climate change is undeniable, and cannot be simply wished away by politicians who lack the courage to confront the scientific evidence,” he wrote.

“[It] should place enormous pressure on the Australian prime minister, Tony Abbott, to make it a major agenda item at the G20 summit later this month, instead of shunting it to the sidelines.

The G20 summit would provide the most effective platform for world leaders to discuss transitioning to a low-carbon economy, he wrote.

“Yet the local politics of a country of less than 25 million is being allowed to prevent essential strategic discussions of an issue that is of fundamental importance to the prosperity and well-being of the world’s population of 7 billion people.”

The IPCC report provides evidence of the impact climate change is already having around the world through rising temperatures, shifts in extreme weather, disappearing glaciers and ice sheets, and advancing sea levels.

Avoiding the worst impacts of climate change would mean staying below the threshold warming of 2 degrees, the report says, which will only be achieved if annual emissions will need to be reduced by about half by 2050 compared with 2010.

“The IPCC report makes plain that further delays in tackling climate change would be dangerous, and ‘wait and see’ would be a profoundly irrational policy,” Stern wrote.

“The report should be high on the agenda for the leaders of the world’s 20 most powerful nations, responsible for the majority of the world’s greenhouse gas emissions, when they meet in Brisbane on 15 November.”

In August, a group of medical scientists led by the Nobel laureate Prof. Peter Doherty published an open letter Abbott urging him to make climate change a G20 agenda item and reduce carbon emissions.