Build a giant wall.  6,000 kilometers long.  Made out of sand.  Stuck together with bacteria.  No, seriously.

"The threat is desertification. My response is a sandstone wall made from solidified sand," said Mr Larsson, who describes himself as a dune architect.

The sand would be stabilised by flooding it with bacteria that can set it like concrete in a matter of hours.

Take his word for it; he's a dune architect.  And desertification is not something to mess around with.  It's poised to affect over 2 billion people in 140 countries if left unchecked.  But with a gigantic, bacteria-reinforced dune wall, buttressing a "Great Green Belt" of trees, unchecked it will not be.  As long as we can figure out minor details like politics, funding, and where to obtain "giant bacteria-filled balloons."

If this seems similar to ad hoc geo-engineering schemes of righting the climate, well, it does to me, too.  Except that I'm more comfortable building walls to stop desertification than, say, attaching tubes to giant zeppelins that pump the air full of sulfur dioxide to block the sun and cool the planet.

(image from flickr user John Spooner under a Creative Commons license)