The report was meant to ring alarm bells about global warming, noting that temperatures are likely to be 1.5 degrees higher by 2030 to 2052 based on current commitments to reduce emissions made under the Paris deal. Countries in the southern hemisphere will be among the worse off, the report said.
One expert - Appalachian State University environmental scientist Gregg Marland - said limiting global warming to either 1.5 or 2 degrees seems unlikely.
While warming of 2C above pre-industrial levels has widely been thought of as the threshold beyond which unsafe climate change will occur, vulnerable countries such as low-lying island states warn rises above 1.5C will threaten their survival.
Limiting global warming to 1.5C will cost the world $2.4 trillion every year for the next two decades, the United Nations report warns. While an increase of that magnitude would boost sea levels by as much as 77 centimetres by the end of the century, that would be about 10 centimetres lower than at 2 degrees, the report said.
The report summary said renewable energy would need to supply 70 per cent to 85 per cent of electricity by 2050 to stay within a 1.5C limit, compared with about 25 per cent now.
"Every extra bit of warming matters, especially since warming of 1.5°C or higher increases the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems", Co-Chair of IPCC Working Group II Hans-Otto Pörtner said.
"Limiting global warming would also give people and ecosystems more room to adapt and remain below relevant risk thresholds".
The IPCC, the UN's top climate panel, issued the report from Incheon, Republic of Korea, where for the past week, hundreds of scientists and government representatives have been pouring over thousands of inputs to paint a picture of what could happen to the planet and its inhabitants with global warming of 1.5°C (or 2.7 degrees Fahrenheit).
Lowering emissions to this degree, while technically possible, would require widespread changes in energy, industry, buildings, transportation and cities, according to the report. For Canada, that means emissions would need to fall to a maximum of 385 million tonnes a year.
The IPCC says that to achieve this target would require "rapid, far-reaching, and unprecedented changes in all aspects of society". Allowing the global temperature to temporarily exceed or "overshoot" 1.5ºC would mean a greater reliance on techniques that remove Carbon dioxide from the air to return global temperatures to below 1.5°C by 2100.
The effectiveness of such techniques are unproven at large scale and some may carry significant risks for sustainable development, the report notes.
A report released on Monday, which references more than 6000 scientific studies, says there are major benefits if global warming is limited to 1.5C compared to 2C.
"It's a line in the sand and what it says to our species is that this is the moment and we must act now", said Debra Roberts, a co-chair of the working group on impacts.
The report calls for immediate and radical action by all global governments, saying the required actions are affordable and feasible but require ambition and dedication. It needs really, really radical changes in terms of emissions reduction if you're going to avoid all the climate change impacts that go with warming beyond 1.5 degrees.