The long-term fate of New Orleans is disaster. it's built within a giant delta - the accumulating deposits of the Mississippi river. These sediments are deposited principally in floods and also in normal channel flow. 10 Km of sediment has accumulated in the past 5 Ma or less.

That sediment is compacting under its own weight, squeezing the water out from between the grains and the grains are re-adjusting - getting dented by their neighbours and packing closer together. The consequence is subsidence.

The load imposed on the crust is also causing regional-scale subsidence. The ground level today will be 1 km under water in 0.5 Ma, UNLESS you allow the river to flow through town and build it up with sediments. That's 10m (a storey) in 5,000 years, or faster on a local basis.

There aren't enough trucks in the USA to economically deliver that volume of crushed rock and keep building it up. You have to rely on the massive and free power of mother nature.

When people lived in mud and stick huts, the river flooded most years, and built up the land and you rebuilt your hut when it got too low. In the modern era we have done quite the opposite and the essence of flood control policy has been to keep the river and its sediment load out of town.

I suggest that you could go for a Venice-like solution with high-rise towers linked by slightly flexible ties, and piled deep into the subsoil (there ain't no bedrock here for 35, ooo ft!). You'd connect the buildings by bridges and walkways and build quaysides to get on and off boats for transport. Maybe even have a network of aerial roads, given the USA love affair with the car.

As subsidence lowered the regional ground level, the buildings would sink gradually lower, losing a storey every few centuries, or whatever. The floods would bring more sediment to fill between the buildings. Some areas would become "dry" land (but on the boggy side) and could become parks. Others would be floodways and dredged navigation channels. Year by year, this would change.

As the buildings foundered, you'd pump cement and clean waste into the basements to counter the pressure of sediment outside, or simply let the windows pop and the mud slump in.

The only other alternative is to have a series of parallel levees through town and each decade or two, let the river flow through and sediment a different strip of city - abandoning 10% of the city at a time to nature, rather than all at once.

Of course, what we're observing now is that it's all a bit too late. N'Orleans has been living off borrowed time for a Century, and the time just ran out.

Many other coastal cities round the world face similar problems. Venice is sinking, London had to build a storm-surge barrier and in a century or two that will be obsolete.

The sad fact is that many major cities are built on Deltas and deltas are characterised by subsidence and eventual flooding. It's nature's way.

We should be building cities on elevated plateaux, well away from Earthquake fault zones and volcanoes. But most of the cities in the world developed centuries before we understood the processes of nature.

Now, add to all this predictable and natural subsidence, the possible dangers of future global warming (whether it be anthropogenic or natural, or a bit of both). Weather pattern swill change and in some decades or centuries, storms will be more frequent and destructive than in others.

Although the film "Day after tomorrow" was sensationalist and its timing grossly exaggerated, we KNOW as geologists that climate change is real. The Aboriginal settlers of Australia walked to Tasmania within oral history. Now it's a 10-hour boat ride. Several waves of humans crossed the Bering straits on foot. Viking ports are now hundreds of miles inland on the shrinking Baltic sea.

Either the sea will go up or it will go down. And not by inches but by dozens or hundreds of feet, over a timeframe of 1000-10,000 yr.

Be prepared to build dykes, or relocate ports. One way or the other the world will change, as it has changed in the past. We frail humans aren't smart enough to balance climate to make the world stay still!