At current rates global temperatures will have risen by an average 1.5 degrees between 2030 and 2055, the United Nations Intergovernmental Panel on Climate Change (IPCC) warns.

Human activities are estimated to have already caused a one-degree rise above pre-industrial temperatures, today’s special report says.

Limiting global warming to 1.5 degrees will require “rapid, far-reaching and unprecedented changes” at all levels of society.

Man-made carbon dioxide emissions must fall by about 45% from 2010 levels by 2030 and reach “net zero” in about 2050.

“Every extra bit of warming matters, especially since warming of 1.5 degrees or higher increases the risk associated with long-lasting or irreversible changes such as the loss of some ecosystems,” IPCC Working Group II Co-Chairman Hans-Otto Portner said.

The global sea level rise would be 10cm lower under a 1.5-degree warming scenario compared with two degrees or higher, the UN says.

Coral reefs, including the Great Barrier Reef, would decline by 70-90% as opposed to a 99% chance of elimination at two degrees.

The special report was prepared at the request of signatories to the 2015 Paris Agreement.

See ANALYSIS.