Climate change will become irreversible without a host of major transformations that are "unprecedented in scale", a landmark UN report has warned.

Humans have already caused global warming to rise 1°C above pre-industrial levels. But that is set to reach 1.5°C between 2030 and 2052 on current trends.

At this point, heatwaves, heavy rains, droughts, wildfires and coastal flooding would all become much more common across the globe.

Experts say time is running out to prevent these and an an array of other disasters, including mosquito borne diseases such as malaria, dramatically depleted fisheries and widespread crop failures.

Carbon neutral by 2050 to be in with half a chance

To have at least a 50/50 chance of staying under the 1.5°C cap, the world must become "carbon neutral" by 2050, according to the new report.

"That means every tonne of CO2 we put into the atmosphere will have to be balanced by a tonne of CO2 taken out," said lead coordinating author Myles Allen, head of the University of Oxford's Climate Research Programme.