People are always talking about 'the problem of youth'. If there is one -- which I take leave to doubt -- then it is older people who create it, not the young themselves. Let us get down to fundamentals and agree that the young are after all human beings -- people just like their elders. There is only one difference between an old man and a young one: the young man has a glorious future before him and the old one has a splendid future behind him: and maybe that is where the rub is.
When I was a teenager, I felt that I was just young and uncertain -- that I was a new boy in a huge school, and I would have been very pleased to be regarded as something so interesting as a problem. For one thing, being a problem gives you a certain identity, and that is one of the things the young are busily engaged in seeking.
I find young people exciting. They have an air of freedom, and they not a dreary commitment to mean ambitions or love of comfort. They are not anxious social climbers, and they have no devotion to material things. To me, all this seems to link them with life, and the origins of things. It's as if they were, in some sense, cosmic beings in violent and lovely contrast with us suburban creatures. All that is in my mind when I meet a young person. He may be conceited, ill-mannered, presumptuous or fatuous, but I do not turn for protection to dreary cliches about respect of elders -- as if mere age were a reason for respect. I accept that we are equals, and I will argue with him, as an equal, if I think he is wrong.
These two timescales are instantly recognisable to anyone familiar with Earth's ice ages: for the past million years, ice ages have occurred roughly every 100,000 years. Before that, they occurred roughly every 41,000 years.
Most scientists believe that the ice ages are the result of subtle changes in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the way Earth's orbit gradually changes shape from a circle to a slight ellipse and back again roughly every 100,000 years. The theory says this alters the amount of solar radiation that Earth receives, triggering the ice ages. However, a persistent problem with this theory has been its inability to explain why the ice ages changed frequency a million years ago.
"In Milankovitch, there is certainly no good idea why the frequency should change from one to another," says Neil Edwards, a climatologist at the Open University in Milton Keynes, UK. Nor is the transition problem the only one the Milankovitch theory faces. Ehrlich and other critics claim that the temperature variations caused by Milankovitch cycles are simply not big enough to drive ice ages.
However, Edwards believes the small changes in solar heating produced by Milankovitch cycles are then amplified by feedback mechanisms on Earth. For example, if sea ice begins to form because of a slight cooling, carbon dioxide that would otherwise have found its way into the atmosphere as part of the carbon cycle is locked into the ice. That weakens the greenhouse effect and Earth grows even colder.
According to Edwards, there is no lack of such mechanisms."If you add their effects together, there is more than enough feedback to make Milankovitch work," he says. "The problem now is identifying which mechanisms are at work." This is why scientists like Edwards are not yet ready to give up on the current theory. "Milankovitch cycles give us ice ages roughly when we observe them to happen. We can calculate where we are in the cycle and compare it with observation," he says. "I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation."
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1. The ice ages changed frequency from 100,000 to 41,000 years a million years ago.
2. The sole problem that the Milankovitch theory can not solve is to explain why the ice age frequency should shift from one to another.
3. Carbon dioxide can be locked artificially into sea ice to eliminate the greenhouse effect.
4. Some scientists are not ready to give up the Milankovitch theory though they haven't figured out which mechanisms amplify the changes in solar heating.
Both Edwards and Ehrlich believe that there is no practical way to test when the solar temperature scillation begins and when ends.