IN a doomsday scenario straight out of the Matrix trilogy, top scientist Tim Flannery has claimed humanity may need to blot out the sun to survive global warming.

The former Australian of the Year says sulphur could be pumped into the Earth's stratosphere to keep out the sun's rays and slow global warming, a process called global dimming.

"It would change the colour of the sky," Professor Flannery said.

"It's the last resort that we have, it's the last barrier to a climate collapse.

"We need to be ready to start doing it in perhaps five years' time if we fail to achieve what we're trying to achieve."

In the Matrix trilogy, the human resistance "scorches the sky" to block out the sun and deny humanity's man-made mechanical enemies solar energy.

Now a similar strategy is being proposed to counter another human-created threat that's just as grave.

Professor Flannery said climate change was happening so quickly that mankind may need to resort to his radical plan to survive.

He said the sulphur could be dispersed above the Earth's surface by adding it to jet fuel.

He conceded there were risks to global dimming via sulphur.