Warm-up to the main event

By now, I expect that everyone has heard about the Pentagon report that presents global climate change as a real threat and a national security issue. The headline grabber was the possibility of a "tipping point" that could cause a rapid shift in climate along with the prediction that such a tipping point could come within the next 20 years, a tipping point that would plunge northern Europe into a deep freeze.

I actually made note of the fact that the Pentagon had such a report over a month ago, on February 4. And the idea on which it's based was being discussed by climatologists a few years ago - so it's the attention being given to it that's news, not the idea itself.

Since it can be hard to understand how global warming can lead to a significantly colder Europe, here's a simplified explanation. (NASA has a more detailed explanation here.)

First thing is to realize that by latitude, London is around 51 degrees north - about the same as the Strait of Belle Isle between Newfoundland and Labrador. But it's winters are much milder. That's because there is a current that carries warm water from the tropics into the northeast Atlantic, moderating the climate. What keeps that stream going is that the northern waters are colder and saltier - the latter because a good amount of fresh water is locked up in ice. That colder, saltier water is denser (has more mass per unit volume) than the warmer, less salty water, so it sinks below it. As more such water sinks behind it, that water gets pushed south underneath the northbound warm current, back to the topics, where it is gradually warmed, becomes less dense, rises to the surface, and the pattern continues.

The point is that one of the main things that keeps that current going is the difference in salinity - and therefore density - of the waters from the tropics and from the poles. With global warming, the average temperature of the Earth rises. If it rises enough, the polar ice caps begin to melt - as in fact they already are doing. That dumps fresh water into the polar oceans, reducing their salinity. Reduce it enough, and the difference between tropical and polar water is no longer enough to cause the polar water to sink below the tropical water. The result: The current shuts down, the warm water stops being brought north - and London becomes Labrador.

However, my real reason for raising this is that one of the less-noted aspects of that report is that it predicted that future wars will be more over resources like water than over borders or ethnicities.

With that in mind, consider this from the BBC for March 7:

The 10 states that share the Nile waters are meeting in Uganda on Monday to discuss the future of the river.

The talks - held under the auspices of the Nile Basin Initiative - come amid growing regional tensions over the world's longest river.

Egypt is reported to have said it would regard any attempt to alter the Nile status as an act of war.

A 1929 treaty said no work would be done on the river that would reduce the volume of water reaching Egypt.

The Nile is vitally important to the survival of 160 million people who share the basin in which it flows, but to Egypt the river is a matter of life and death, as the country has almost no other source of water.

But the 1929 treaty - signed between Britain and Egypt - is now being questioned.

Tanzania is building a pipeline to extract drinking water.

Kenya is calling for a revision of the treaty, and Ethiopia is planning to use the water for irrigation.

The idea of the meeting is to "thrash out" a common agenda for the river - but the very fact that such a meeting is necessary is significant.