"Limiting warming to 1.5°C is possible within the laws of chemistry and physics but doing so would require unprecedented changes", said Jim Skea, co-chair of IPCC Working Group III. "Several regional changes in climate are assessed to occur with global warming up to 1.5 degree Celsius compared to pre-industrial levels, including warming of extreme temperatures in many regions (high confidence), increases in frequency, intensity, and/or amount of heavy precipitation in several regions (high confidence), and an increase in intensity or frequency of droughts in some regions (medium confidence)". Coral reefs are projected to decline 70% to 90% at 1.5 degrees C, but at 2 degrees, 99% of reefs would be ravaged.
"We welcome the conclusions of this historic report, one that should give the global community not just a wake-up call, but also hope that we can avoid the most devastating impacts of climate change", said Bill Hare, Climate Analytics CEO.
The world is already experiencing around 1C of global warming, and events such as floods, storms and heatwaves like the one in the United Kingdom this summer have become increasingly likely as a result of climate change, according to experts. The report emphasises the need for placing climate change at the centre of all national and global agendas.
Lowering emissions to this degree, while technically possible, would require widespread changes in energy, industry, buildings, transportation and cities, according to the report.
To contain warming at 1.5C, manmade global net carbon dioxide (CO2) emissions would need to fall by about 45% by 2030, the report warned.
Meeting the 1.5C limit would demand "rapid, far-reaching and unprecedented change in all aspects of society", the panel said.
The decisions we make today are critical in ensuring a safe and sustainable world for everyone, both now and in the future, said Debra Roberts, Co-Chair of IPCC Working Group II.
Should governments fail to do that within a decade, and temperatures rise more than 1.5 degrees C, there's one more Hail Mary option.
US President Donald Trump has questioned the science of manmade climate change and vowed to withdraw the US, the world's second largest emitter of greenhouse gases after China, from the agreement. The atmosphere is nearly 1 degree Celsius (1.8 Fahrenheit) hotter than it was at the start of the industrial revolution, and burning more fossil fuels will accelerate the shift toward higher temperatures, the group said in its report.
Based on more than 6 000 peer-reviewed studies, the 20-page bombshell will make for grim reading when it is released on Monday.
Intergovernmental Panel on Climate Change chair Hoesung Lee, centre, speaks during a news conference in Incheon, South Korea, on Monday. "Depending on how gas is used and how successful carbon capture and storage (CCS) is, natural gas use is reduced by more than 50 percent or stays roughly similar to 2010 levels".
"Large quantities of current gas plants will need to be retired early, while those under construction or in planning stages must be reconsidered immediately as they are not compatible with the 1.5-degree future", Chen said.
"There were doubts if we would be able to differentiate impacts set at 1.5C and that came so clearly".
"The report shows that we only have the slimmest of opportunities remaining to avoid unthinkable damage to the climate system that supports life as we know it", said Amjad Abdulla, the IPCC board member and chief negotiator for an alliance of small island states at risk of flooding as sea levels rise.
The planet is already two-thirds of the way there, with global temperatures having warmed about 1 degree C.
Methods to take excess carbon out of the atmosphere will also be needed. Annual carbon dioxide pollution levels that are still rising now would have to drop by about half by 2030 and then be near zero by 2050.
Despite the controversial policy implications, the USA delegation joined more than 180 countries on Saturday in accepting the report's summary for policymakers, while walking a delicate diplomatic line.
"It will take government resolve", he said.