(Here's a handy graphic to explain the differences between 1.5 and 2 degrees Celsius of warming.) The IPCC's report drew information from more than 6,000 scientific studies and 132 authors.
Fifteen years later, the UNFCCC's Copenhagen Accord introduced a 2℃ target, and its 2015 Paris Agreement was even more specific: it "aims to strengthen the global response to the threat of climate change ... by holding the increase in ... temperature to well below 2℃ above pre-industrial levels and pursuing efforts to limit the ... increase to 1.5℃".
The world has seen 1C of warming so far, with consequences such as more extreme weather already being felt, and there is more to come as temperatures continue to rise, the report said.
"The next few years are probably the most important in our history", Debra Roberts, co-chair of the IPCC Working Group II, said in a statement marking the report's release.
As part of the decision to adopt the Paris Agreement, the IPCC was invited to produce, in 2018, a Special Report on global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways.
Lowering emissions to this degree, while technically possible, would require widespread changes in energy, industry, buildings, transportation and cities, according to the report.
The report was prepared at the request of governments when the global pact to tackle climate change was agreed in Paris almost three years ago.
The Paris accord was signed three years ago by nearly 200 nations, who pledged to keep warming to 1.5-2 degrees.
"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.
The path to a climate-safe world has become a tightrope, and will require an unprecedented marshalling of human ingenuity, the authors said.
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Still, Cleetus says that we have most of the technology we need to make the change.
"International cooperation is absolutely imperative to limit emissions and therefore global warming and its impacts, as well as coordinating effective and widespread adaptation and mitigation", said Sarah Perkins-Kirkpatrick, a fellow at the Climate Change Research Center at the University of New South Wales.
Coral reefs will also be drastically affected, with between 70 and 90 per cent expected to die off, including Australia's Great Barrier Reef. "And it just may be enough to save most of the world's coral reefs from dying". By 2050, we would have to hit net zero emissions-any remaining emissions would have to be counteracted by active removal of Carbon dioxide from the atmosphere.
According to Greenpeace India, with an ambitious target of 175 GW of renewable energy by 2022, India can indeed help in keeping global temperature rise below 1.5 degree celsius, but at the same time India's needs to relook at its future energy investments into coal and oil.
That could reduce flooding and give the people that inhabit the world's coasts, islands and river deltas time to adapt to climate change. "It is crucial to keep temperature rise well below 1.5 degrees without offsetting, carbon markets, and geoengineering, but the evidence presented by the IPCC shows that there is a narrow and shrinking window in which to do so". They include a speculative section warning that sea-level rise would make hurricane storm surge in Miami far worse.
But that is a big ask, considering we released more carbon dioxide into the atmosphere previous year than ever before.
Using carbon capture and storage (CCS) technology, the share of gas-fired power would need to be cut to 8 percent and coal to under 2 percent.
The report summary said renewable energy would need to supply 70 percent to 85 percent of electricity by 2050 to stay within a 1.5C limit, compared with about 25 percent now.
The Paris Agreement on Climate Change was expected to produce a new urgency but the United States pullout from the accord dented those hopes. But Monday's report comes amid a reactionary political climate. "If we changed to fulfil health recommendations, we'd all live longer and bounce around much more and have nicer lives and we'd also reduce greenhouse gas emissions".