Before the Paris Agreement was inked in 2015, almost a decade of scientific research rested on the assumption that 2C was the guardrail for a climate-safe world.
The report found that the world is already experiencing the impacts of rapid and unequivocal global warming such as the decline of coral reefs, sea level rise, Arctic sea ice loss, decreasing biodiversity, declining crop yields, more frequent heatwaves and droughts in some regions, and heavy rainfall events in others.
The report outlined the changes they believe need to be made for the temperature rise to be limited to 1.5ºC "The good news is that some of the kinds of actions that would be needed to limit global warming to1.5ºC are already underway around the world, but they would need to accelerate", said Valerie Masson-Delmotte, Co-Chair of Working Group I.
Portner warned, however, "If action is not taken, it will take the planet into an unprecedented climate future". "There is no time to waste".
Scotland's new Climate Change Bill, published earlier this year, proposes reducing harmful emissions by 90% by 2050 - up from the previous target of 80%. "The latter would be used as part of a now nonexistent program to get power from trees or plants and then bury the resulting carbon dioxide emissions in the ground, leading to a net subtraction of the gas from the air - bioenergy with carbon capture and storage, or BECCS".
"The coming period is critical".
The IPPC report represents "sobering assessment of the challenge we face, and of the risks and costs of a warming planet", Caroline Theriault, a spokeswoman for Environment Minister Catherine McKenna, said.
The recommendations could offer scientific guidance to policymakers on how to reduce emissions from sectors like electricity, transport, buildings and agriculture to not exceed global temperature rise of more than 1.5 degrees from pre-industrial levels.
Sue Reid, vice president of climate and energy for Ceres, a sustainability leadership advocate that has for years called on the industry to do more to battle climate change, called the new IPCC report a "striking wakeup call to action". Intergovernmental Panel on Climate Change. But a lower temperature increase would allow humanity more precious time with which to adapt to the adverse conditions presented by climate change.
One expert - Appalachian State University environmental scientist Gregg Marland - said limiting global warming to either 1.5 or 2 degrees seems unlikely.
The report, which maps out four pathways to cap Earth's average surface temperature at 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels indicates that changes in individual behavior can make a difference.
"Climate impacts are exponentially more dramatic when we go from 1.5C to 2C", said Henri Waisman, a scientist at the Institute for Sustainable Development and International Relations, and a coordinating lead author of the IPCC report.
Aiming to limit global warming at 1.5℃ is a mammoth task at hand, it requires a massive social transformation in the way we consume energy. "It really reduces the impacts of climate change in very important ways", said Prof Jim Skea, who is a co-chair of the IPCC.
Global warming, aka climate change, is caused by the burning of fossil fuels such as oil, gas and coal that release greenhouse gases like carbon dioxide, which has warmed the planet to levels that can not be explained by natural causes.
These carbon dioxide scrubbing techniques would be particularly vital if the global temperature were to briefly peak above 1.5°C before being wrestled back down below the target by the end of the century.