The stately progress of the River Nile through Africa was nicely captured recently in the Bulletin of the World Meteorological Organisation:
"The legendary Nile springs south of the equator in Burundi, and flows through lake Victoria before thundering down the Murchison Falls to Lake Mobutu. Then it saunters through the milliards of runnels of the Sudd, one of the world's biggest swamps, losing about 70 per cent of its water by evapotranspiration. The Nile then enters stony desert, before plunging down a dozen basaltic cataracts to Khartoum, the capital of Sudan.
"At Khartoum, the lethargic White Nile is rejuvenated, mainly during the rainy season, by the turbulent Blue Nile which descends from the lofty Ethiopian highlands. And finally the river pours into the Mediterranean Sea through a huge delta after a journey which has covered half the African continent and thousands of years of human civilisation."
But there are fears that the Nile may be about to affect our global climate. More specifically, it has been suggested that Egypt's Aswan Dam may ultimately plunge Europe into another ice age.
The High Dam at Aswan was built in the 1960s to maintain the river's level, but more water was extracted for irrigation. The net result was a reduction in the amount of fresh water reaching the Mediterranean Sea.
This, the argument goes, must have increased the Mediterranean's salinity, and hence its density, and this more substantial water should be better at surging through the Gibraltar Straight than was its fresher counterpart.
Once in the Atlantic, apparently, outflow from the straight flows north. Some say that a more vigorous outflow, therefore, could have the effect of nudging the Gulf Stream closer to Greenland than it is at present - close enough, in fact, for some of its balmy waters to be diverted west of Greenland into the Labrador Sea. If this should happen, our fate, it seems, is sealed.
A warmer Labrador Sea means more evaporation in that region, more water vapour in the atmosphere, and therefore more snow to fall and swell the polar ice caps. Once started, the process will accelerate, because more solar radiation will be reflected from the ever larger areas of ice - and thus the Arctic ice cap will creep inexorably southwards over Europe.
But there is a way to prevent this Armageddon, proponents of this interesting theory believe - and they propose it not entirely tongue in cheek. The solution is a simple one: construct another massive dam across the Straight of Gibraltar to reduce the outflow from the Mediterranean.