Weather could rain on athletes' parade
The London Olympic Games will present, from an environmental perspective, an entirely different challenge to anything faced in the previous two Games.
In Athens in 2004 and Beijing in 2008, much of the concern before the Games was around the effects that heat, humidity, and air pollution would have on athletes. In awarding the Games to these two cities, the Olympic committee effectively chose to expose elite athletes to some of the most polluted air in the world, and during the hottest summer months.
Ultimately, these concerns proved largely unfounded, though they did inspire some interesting actions on the part of competing nations, and the host city, to minimise the effects of the two factors.
The larger nations sent scientists to the venues exactly one year before to sample the air and water so that they could give credible advice to athletes on how to stay "safe".
Some athletes withdrew - the great Haile Gebrselassie decided not to run the marathon in Beijing because of the pollution and concerns about his asthma.
Some nations handed masks to athletes to filter out "poisonous" air, creating a diplomatic crisis when athletes stepped off their planes wearing hazard masks, offending their Chinese hosts.
Beijing instituted laws that would cut the number of cars on the road in half, and closed factories in an attempt to get the air quality to acceptable levels.
London 2012 faces no such concerns, fortunately. Nor is the potentially debilitating heat of summer a factor.
Ever since Atlanta 1996, scientists have been concerned about the effects of heat on athletes because the Games, by definition, take place in the northern hemisphere summer.
Scientists have often advised that events such as the marathon should be cancelled when conditions become too hot because the temperature might be dangerous or fatal for runners. That's never happened (TV broadcast rights and money speak louder!) and has never been necessary. As warm as it has been at some Olympics, elite athletes are conditioned for heat and able to stay safe by adjusting their pace.
The result is that, instead of seeing the typical 2hrs 06min marathon, we see winning times of 2:10 to 2:14, but no inherent danger to the athletes.
One of the interesting consequences of higher temperatures is that they tend to favour smaller runners because small people store less heat and therefore have less chance of overheating during exercising.
It's no coincidence, physiologically speaking, that our own Josiah Thugwane won a hot, humid Olympic marathon in Atlanta in 1996 because, not only was he a superbly trained athlete, he was also the smallest man in the race at only 45kg. Similarly, when Kenya's Sammy Wanjiru won the marathon in hot, humid Beijing, he did so in part because of his small size - he weighed only 51kg. The smallest man in this race, incidentally, was third - so it pays a marathon runner to be little.
These are moot points ahead of London because long-range forecasts suggest that the risk of drowning in nonstop rain is probably greater than anything related to heat.
This is good news for some (the endurance runners) but bad news for others. Any event in which technical skill is needed (hurdles, cycling, archery, throws, pole vaulting, for example) will be unpredictable and we can expect surprises as a result of who deals with the weather conditions best. Also, if it rains for the men's 100m final, a world record is highly unlikely.
So it might not be heat, but rain, that is the uncontrollable variable that affects the destination of at least some of London's medals.
Tucker is a research scientist at UCT's Sports Science Institute. His column on the Olympics will appear every Wednesday until the end of the Games. Follow him on twitter @scienceofsport