The world is headed for a "climate catastrophe", UN chief Ban Ki-moon warned Monday as ministers opened a frenetic week of talks to forge a 195-nation accord to brake global warming.

"The clock is ticking towards a climate catastrophe," the UN secretary general told policymakers in Paris, pressing for regular reviews of the deal before it comes into effect in 2020 to ensure mankind is on target to limit warming of the planet to less than 2.0 degrees Celsius (3.6 degrees Fahrenheit) above pre-Industrial Revolution levels.