They say the global community should focus less on how much carbon can still be emitted and more on setting concrete timelines for transitioning to a net-zero carbon world.
Released Sunday, the report warned that the world is rapidly running out of time to scale back greenhouse gas emissions before catastrophic planetary changes occur.
Half a degree more (about.9 F) might sound small.
- There would be fewer deaths and illnesses from heat, smog and infectious diseases. It would cut in half the number of animals and plants that would lose habitats with the attendant risk of extinction.
A world with 2°C of warming will be a planet without coral reefs.
The IPPC report represents "sobering assessment of the challenge we face, and of the risks and costs of a warming planet", Caroline Theriault, a spokeswoman for Environment Minister Catherine McKenna, said.
Limiting warming to 1.5 degrees would also give the world a better chance of avoiding major tipping points like the collapse of the West Antarctic Ice Sheet. People will have to change their energy use and even the foods they eat.
Experts estimate that cutting down on SLCPs could reduce global warming by as much as 0.5 degrees C. That would not be enough to avoid the worst effects of climate change if we continue to burn fossil fuels, but it could buy humanity some much-needed time while carbon emissions are brought under better control. But he says it is not impossible. It's called the 2-degree goal.
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.
Limiting warming to 1.5°C is possible within the laws of chemistry and physics but doing so would require unprecedented changes, Co-Chair of IPCC Working Group III Jim Skea said.
The climate modelling called socioeconomic pathways, or SSPs, looks at choices individuals can make to contribute towards the 1.5 degrees Celsius limit on global warming based on pre-industrial levels.
The IPCC does not do any of its own research, so the report draws on more than 6,000 research papers to reach its conclusions. Coral reefs would decline by 70 percent to 90 percent with global warming of 1.5 degrees Celsius, whereas virtually all would be lost with 2 degrees Celsius.
One of the lead authors, Murdoch University climate scientist Jatin Kala, said even if global warming was kept to 1.5C there could still be "dire consequences" for WA's South West, such as altered growing seasons in the Wheatbelt and wine regions such as the Swan Valley.
"I just don't see the possibility of doing the one and a half" and even 2 degrees looks unlikely, said Appalachian State University environmental scientist Gregg Marland, who isn't part of the United Nations panel but has tracked global emissions for decades for the U.S. Energy Department. He likened the report to an academic exercise wondering what would happen if a frog had wings. The report is relatively optimistic that this can be done, but only with unprecedented commitment and cooperation from governments, industry, religious and secular leaders, and citizens around the world.
"We want a just transition to a clean energy system that benefits people not corporations", Nansen emphasized.
Measures would have to include reducing man-made carbon emissions by 45 per cent by 2030 from 2010 levels, and reaching "net zero" emissions by 2050, the report said.
At current levels of greenhouse gas emissions, earth could pass the 1.5 C marker as early as 2030, and no later than mid-century, the Intergovernmental Panel for Climate Change reports with "high confidence".. The world now pumps more than 40 billion tons of Carbon dioxide into the atmosphere each year; the IPCC calls for that number to be cut by more than 1 billion tons per year over the next decade.
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