Very - the report calls for "rapid, far-reaching and unprecedented changes in all aspects of society".
"What I hope this report will do is change the discourse on mitigation, with countries understanding mitigation not as a burden but as an opportunity", said Diana Ürge-Vorsatz, vice-chair of the Working Group III.
Staying within the 1.5 degrees C target, instead of 2 degrees C, would result in the global sea level rising 3.9 inches less by 2100, reducing flooding.
The report is comprehensive, citing over 6,000 scientific references, and its basic message is this: limiting warming to a rise of 1.5 degrees compared with pre-industrial levels will require an unprecedented amount of effort, but a rise of 2 degrees would be far more harmful and ultimately more costly, too.
Even in the best-case scenario, where global warming is capped at 1.5 °C by the end of the century, its effects will most likely be devastating. Trillions of dollars will soon be invested in new infrastructure; if we make the wrong choices, they'll be locked in, according to the same recent report.
Researchers found that "human caused" C02 emissions need to be cut by almost half of 2010 levels by the 2030 to starve off the worts effects of climate change.
Atiku wins PDP Presidential Primary
We will not lose the momentum but sustain it to rebuild Nigeria and elect Alhaji Atiku Abubakar as the next President of Nigeria. He said the process that led to the election was more important as all the aspirants were qualified to lead the nation.
Temperatures have already risen an average 1C since the mid-1800s as industrialisation fuels the growth of carbon dioxide emissions (CO2), the main greenhouse gas blamed for climate change.
"Limiting warming to 1.5 C is possible within the laws of chemistry and physics", says Jim Skea of Imperial College London, one of the authors of the report, "but doing so would require unprecedented changes".
The report will be a key scientific input into the Katowice Climate Change Conference in Poland in December when governments will review the Paris Agreement to tackle climate change.
The report finds that renewable energy must make up half of the global energy mix by 2050, and coal needs to be out of the power sector altogether by then.
The science shows that a 2C rise will lead to greater sea level rises, more heatwaves and extreme rainstorms, more people facing water shortages and drought, lower yields for some crops and greater impacts on wildlife than 1.5C.
"There were doubts if we would be able to differentiate impacts set at 1.5C and that came so clearly".
Professor Corinne Le Quere, from the University of East Anglia, said: "For the United Kingdom, this means a rapid switch to renewable energy and electric cars, insulating our homes, planting trees, where possible walking or cycling and eating well - more plants and less meat - and developing an industry to capture carbon and store it underground".
"1.5 degrees is the new 2 degrees", Jennifer Morgan, executive director of Greenpeace International, told The Washington Post after attending the finalisation of the IPCC report in Incheon, the Republic of Korea.
The effectiveness of such techniques are unproven at large scale and some may carry significant risks for sustainable development, the report notes.