The latest IPCC report comes ahead of the Katowice Climate Change Conference in Poland in December, where the world's governments will examine progress made in holding to the Paris Agreements of 2015.
The report found that if greenhouse gas emissions continue to grow at their current rate, the earth's atmosphere will warm up by as much as 1.5ºC above pre-industrial levels by 2040.
The 2015 Paris Agreement - which applies to Hong Kong - highlighted the need to limit the rise in average temperatures to 2 degrees over the century from pre-industrial levels to stave off the worst and irreversible effects of climate change, while "pursuing efforts" to achieve 1.5 degrees.
The IPCC report says that the next few years are probably the most important in human history and the decisions we make today about climate action are critical.
The reports warns "unprecedented action" is need to make sure global temperature increase is limited to 1.5 degrees, including human-caused carbon dioxide (CO2) emissions reducing by 45 percent by 2030, with that figure going to near-zero by 2050.
The IPCC report says we need "rapid and far-reaching" changes in energy systems, land use, city and industrial design, transportation and building use.
Limiting the increase to 1.5 degrees would also have a dramatic impact on economic growth and development in poorer countries, which could reduce the number of people both exposed to climate-related risks and susceptible to poverty by several hundred million by 2050, it said.
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.
The leading body of climate change researchers has urged world leaders to commit to limiting global warming to 1.5 degrees Celsius rather than the original commitment of below 2 degrees.
While 1.5°C rise in global temperature will be precarious, a 2°C rise would be catastrophic.
The panel says that keeping warming to 1.5 degrees C is technically feasible, but the emissions cuts pledged so far by the nations that signed the Paris agreement fall far short of what's needed. The report also examines pathways available to limit warming to 1.5 °C, what it would take to achieve them and what the consequences could be. "We're not on track, we're now heading for about 3 degrees or 4 degrees of warming by 2100", Mark Howden, a climate change scientist at Australian National University, said during an online briefing on Sunday. Working Group I assessed the physical science basis of climate change; Working Group II addressed impacts, adaptation and vulnerability; and Working Group III dealt with the mitigation of climate change. Countries with arid and semi-arid climates and those with more continental locations will also warm more than those with predominantly humid and maritime conditions.
A half a degree doesn't sound like much but whether it is coral reefs, crops, floods or the survival of species, everyone and everything is far better off in a world that keeps below 1.5C.
"That means every tonne of Carbon dioxide we put into the atmosphere will have to be balanced by a tonne of Carbon dioxide taken out", said lead coordinating author Myles Allen, head of the University of Oxford's Climate Research Programme. The IPCC 1.5 report starkly illustrates the difference between temperature rises of 1.5°C and 2°C-for many around the world this is a matter of life and death.
The effectiveness of such techniques are unproven at large scale and some may carry significant risks for sustainable development, the report notes. "Each year that the global economy fails to decarbonize at the required rate, the two-degree goal becomes more hard to achieve".
But really whacky ideas, such as blocking out the Sun, or adding iron to the oceans have been dismissed by this IPCC report. Next year the IPCC will release the Special Report on the Ocean and Cryosphere in a Changing Climate, and Climate Change and Land, which looks at how climate change affects land use. "Impacts on natural and human systems from global warming have already been observed (high confidence)".