Thermal coal exports should have a $2 a tonne levy imposed on them to raise $350 million a year for flood mitigation projects, the Australian Greens say.

Greens leader Senator Christine Milne said in Brisbane on Thursday it was time the coal industry was asked to contribute to the conditions it was creating by increasing carbon emissions in the atmosphere.

The Greens are basing their policy push on the truism that prevention is better than cure and point out that Queensland - with two major flood events in two years - would be a major beneficiary of their policy.

"We must prepare for the inevitable, for the more intense extreme weather events," Senator Milne said.

"Over the forward estimates you would raise over $300 million a year and that money would enable you to put this money into disaster relief."