Produced by 91 authors at the request of the group of governments which signed on to the 2015 Paris Agreement, it outlines the impact of global warming of 1.5 degrees Celsuis above pre-industrial levels, and puts forward suggestions to contain global warming below that.
Here's everything you need to know.
Is It A Big Deal?
Claire Perry, minister for energy and clean growth, said the report should "act as a rallying cry for governments around the world to innovate, invest, and raise ambition to avert catastrophic climate change".
Ninety-one authors and review editors from 40 countries prepared the IPCC report in response to an invitation from the United Nations Framework Convention on Climate Change (UNFCCC) when it adopted the Paris Agreement in 2015.
"Every extra bit of warming matters, especially since warming of 1.5ºC or higher increases the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems", says Hans-Otto Pörtner, Co-Chair of IPCC Working Group II, one of three working groups comprising the report, in a press statement.
Chandra Bhushan, the deputy director general of Centre for Science and Environment (CSE), says, "Though it will be very hard in the current global economic system to limit warming to 1.5°C, it is not impossible. The next few years are probably the most important in our history", she said. That's because to confine global warming to 1.5°C, the world needs to cut emissions by 45 per cent by 2030.
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 temperature to below 1.5°C by 2100.
But turning over much more land for energy production "could have implications for food security, ecosystems and biodiversity", the British scientist warned, as competition for land grows.
By 2050, humanity would need to cut its net emissions to zero.
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How Much Global Warming Has There Been Already?
In Hong Kong, the mean sea level in Victoria Harbour went up 31mm per decade between 1954 and a year ago.
Around 6 percent of insects, 8 percent of plants, and 4 percent of vertebrates are projected to be negatively affected by global warming of 1.5°C, namely by shrinking their natural geographic range, compared with 18 percent of insects, 16 percent of plants and 8 percent of vertebrates for global warming of 2°C.
Sea level rises would be 10cm lower with a 1.5C temperature rise compared to 2C by the end of the century.
The IPCC recommends 70-85 per cent of electricity should be generated from renewable sources by 2050 while also finding ways to use technology to reduce emissions by up to 90 per cent.
Small islands and coastal cities such as NY and Mumbai risk going underwater without the installation of sea barriers.
Johnny Chan Chung-leung, director of City University's Guy Carpenter Asia-Pacific Climate Impact Centre, said laws - rather than targets - that mandated a certain ratio of renewables in the power mix by a certain date were also necessary.
What Has Been The Reaction So Far?
There is some good news. We can't find any historical analogies for it. A problem with the Paris accord is that the pledges made do not get the world anywhere near cutting carbon emissions to zero by mid-century, which is what is needed to curb warming to 1.5C. "We need to avoid emissions while reducing poverty".
Organizations and investors that back green energy said the report makes it clear that the world should accelerate the shift away from coal, the most polluting fossil fuel. According to scientific predictions laid out in the report, this amount of warming would likely make extremely hot days both more common and more severe, thus increasing the incidence of forest fires and heat-related deaths. We are already ahead of those targets and are toughening up those targets.