In the 728-page document, the United Nations organization detailed how Earth's weather, health and ecosystems would be in better shape if the world's leaders could somehow limit future human-caused warming to just 0.9 degrees Fahrenheit (a half degree Celsius) from now, instead of the globally agreed-upon goal of 1.8 degrees F (1 degree C).
"We are already seeing the consequences of 1 degree of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice", said Panmao Zhai, one of the co-chairs who helped bring together the report by the researchers who reviewed thousands of scientific papers. Scientists have warned that the enormous changes in energy, transportation and land use required to meet this goal are technically possible, but now appear unlikely.
The report called climate change "an urgent and potentially irreversible threat to human societies and the planet", and warned that delayed action would make it impossible to limit warming to 2.7º F.
However, this does not mean that limiting global warming to 1.5°C will leave us safe.
Carbon emissions need to reach "net zero" by 2050 and almost halve from 2010 levels by 2030.
Envoys at the 2015 Paris talks asked the IPCC to study what it would take to limit warming to 1.5 degrees, a more ambitious goal than the previous 2-degree target.
These are just a few examples taken from a depressingly long list of climate change threats that would be made significantly more risky if the temperature were to rise by 2°C or beyond by the end of the century.
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.
The new report tells us that human activity has already caused about 1℃ of global warming, while at the present rate of warming (0.2℃ per decade) we'll hit 1.5℃ by about 2040.
Reining in the emissions of another greenhouse gas, methane, from the cultivation of cattle, rice and other agricultural products - even as farmers need to feed a growing global population.
Scientists, including some from the Indian Institute of Technology Delhi, had at the time already sounded alarms over climate change as they said it had "exacerbated" the heat wave in the country.
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The report is seen as the main scientific guide for government policymakers on how to implement the 2015 Paris Agreement, which aims to limit the rise in global average temperatures to "well below" 2C above pre-industrial levels, while seeking to tighten the goal to 1.5C.
A landmark United Nations report paints a dire picture of the catastrophic consequences the world will face if immediate action is not taken to limit the global warming to 1.5°C, warning that at 2°C, the world could see 10 cm more global sea level rise, loss of all coral-reefs and worsening food shortages.
Negative impacts of climate change occur on a continuum, and defining a point at which climate change becomes unsafe is hard and contentious.
The lower target would also reduce species loss and extinction and the impact on ecosystems, the report said.
It is thought that by 2100, global sea rise levels would be 10cm lower that if global warming were to be at 2C.
WA's Ningaloo Reef could be wiped out within three decades unless fossil fuels are phased out and the world changes dramatically to deal with a warming planet, according to a landmark report.
"There are material differences between 1.5 C and 2 C", says Cleetus.
What is of particular concern is that the report lowers the level after which disastrous climate change is anticipated: Previous research had set the critical threshold at 2ºC of warming. Any additional emissions would require the removal of Carbon dioxide from the air. When the next climate talks happen this December, the new report is created to give governments the incentive to go much further, faster.
Methods to take excess carbon out of the atmosphere will also be needed.