D. Foster (Letters Echo, January 6) may be “fed up with turbine talk” but destroys his credibility by criticising science he clearly misunderstands.

Navitus Bay’s main threat is not physical but cultural: a massive industrial intrusion endangering the WHS designation. However, could the underwater structures change local silt flows or wave patterns to deleterious effect? I leave that to the oceanographers.

All those studies are right to hedge bets, for natural processes are not predictable to numerical certainty – especially when affected by man. Proof can only follow event. So demanding future ‘proof’ is absurd.

Wind turbines operate cleanly and fuel-free, but what is their real environmental sum, especially off-shore? Whatever the total useful output per machine over its life, what of its energy equivalents in non-salvageable materials (mainly from petroleum by-products), electricity and fuels consumed in its manufacture, erection, maintenance and replacement? Despite their own similar questions, fossil-fuel, nuclear and river-hydroelectric plants’ outputs are continuous and prodigious for machine size.

Mr Foster misinterprets ‘Jurassic Coast’. Our coast did not exist in the Jurassic. Its rocks are Jurassic and Cretaceous, formed in seas of varying levels. Our latitudes were sub-tropical and the continents’ shapes differed from now. Our real ‘Jurassic Coasts’ lie far inland.

The world’s coasts are all dynamic as we are in an Ice Age – alternating warm and cold phases, each tens or hundreds of thousands of years long.

Temperature hence sea-level may rise further, inundating low-lands and altering the coast; then reverse, perhaps reverting S. England to tundra and the English Channel to a river as the sea retreats. When an entire Ice Age ends, the sea could stay high for millions of years. Either way, if human effects are accelerating natural changes, we can only buy a little time.

Portland Bill displays beautiful Ice Age traces: look and think. We cannot be complacent, nor stop natural processes, but we might be able to reduce our contribution to them.

NIGEL GRAHAM Address supplied