"It's now or never".
That's the verdict from the world's leading scientists in a landmark UN report on climate change which came out overnight.
The Intergovernmental Panel on Climate Change report says rapid, systemic transformation is needed across all parts of society to rein in catastrophic global warming.
Even if all the policies to cut carbon that governments had put in place by the end of 2020 were fully implemented, the report says the world will still warm by 3.2 degrees celcius this century.
It says greenhouse gas emissions must peak by 2025 and then be halved this decade, or the world will be hit by "unprecedented heatwaves, terrifying storms, and widespread water shortages."
Victoria University of Wellington Professor of physical geography James Renwick spoke to Corin Dann.
