It was this thought that caused John Martin, once head of the Moss Landing Marine Laboratories in California, to declare, "give me half a tanker of iron, and I'll give you an ice age."

At most airports, traffic controllers organise the approach and landing order of incoming planes in their last half-hour or so of flight.

By midmorning, nearly half of the Americans were wounded, but the militants directed their gunfire on the arriving medevac helicopters, preventing them from landing.