3 years left to save humanity from climate change: experts

Humanity must put carbon dioxide emissions on a downward slope by 2020 to have a realistic shot at capping global warming at well under two degrees Celsius, the bedrock goal of the Paris climate accord, experts said Wednesday.

A world that heats up beyond that threshold will face a crescendo of devastating impacts ranging from deadly heatwaves to mass migration caused by rising seas, the experts warned in a commentary published in the science journal Nature.

With 1.0 degree Celsius (1.8 degrees Fahrenheit) of warming so far, ice sheets that could lift oceans by a dozen metres are melting more quickly, coral reefs are dying from heat stress, and ever more damaging storm surges are hammering coastal communities.

A number of benchmarks should be met by 2020, according to the commentary.

Renewable energy -- mainly wind and solar -- must make up at least 30 percent of the world's electricity supply, it said. Moreover, no additional coal-fired power plants should be approved after that date.

In the transport sector, electric vehicles -- which currently represent one percent of new car sales -- should account for 15 percent of the market by that date.

Governments should also require a 20 percent improvement in fuel efficiency for heavy-duty vehicles, and a 20 percent drop in carbon dioxide pollution per kilometre travelled in the aviation sector.

Still climbing sharply, CO2 from the aviation industry account for about two percent of all human-generated emissions.

Greenhouse gases from deforestation and agriculture, currently about 12 percent of the global total, must be cut to zero within a decade, the experts wrote.