Why Does Winter Happen?

Today, listening to Science Friday on NPR, I learned the answer to a question about which I had long wondered. My question: The winter solstice is on December 22; that is the day on which the sun reaches its most southerly position in the sky. After that, the sun moves gradually farther north every day. My question is, if the sun is moving north, why do the days get colder and colder throughout our winter in the northern hemisphere?

Most people think that the reason our winters occur is because we move farther from the sun during that season. That is not the truth. The earth’s orbit describes an almost perfect circle around the sun, maintaining an almost consistent distance from the sun—there is a slight variation, but it is insignificant.

The earth’s north/south axis is tipped 23° from its horizontal orbit. In the winter, we, in the northern hemisphere are located on the part of the tilt that is away from the sun. This tip causes radiation from the sun to be more diffused than it is in the summer, when the sun’s rays strike the earth in a more perpendicular direction. Therefore, heat from the sun is spread over a larger area, and that heats the surface of the planet less than in the summer.

The reason for the lag in the onset of cold weather after the winter solstice is that the earth soaks up and radiates heat slowly in response to the abundance or the paucity of the sun’s heat radiation. Water, which covers 71% of the earth’s surface, is especially adapted to slow heat transfer. Liquid water is a mitigating influence on rapid changes in weather as the tilted earth rotates around the sun.

We are indebted to the changing seasons for much of life, as we know it. If the earth did not have the 23° tilt, there would be no seasonal changes. This would plunge much of northern Europe, Australia, the southern tips of Africa and South America, and northern Asia into a perpetual ice-crusted no-man’s land. Many crops are dependent upon a changing season system; and that would impair the growth of human populations.

How Beneficial Are Biofuels, Anyway?

We live in a world where species of wild animals are disappearing and a billion people are barely able to get enough to eat. Is this the time to clear rain forests to grow palm oil or give up food-crop land to grow biofuels so that people can burn fuel derived from carbohydrate rather than hydrocarbons in their cars? This paucity of food-producing land is already driving up the cost of food for human populations.Five percent of the world’s crop land has been taken out of growing food and put into growing fuel; in the United States, that figure is 20%. Drought in Australia and more meat eating in China has pushed the world food supply below world food demand. In 2008 the food shortage caused food riots all over the world. Between 2004 and 2007, the world corn harvest increased by 51 million tons; but 50 million tons went into fuel ethanol, leaving nothing to meet the increase in demand for food. American car drivers were taking carbohydrates out of the mouths of the poor to fill their tanks.

This might be okay if the money spent on ethanol would save Americans money so they could afford to buy more goods and services from the poor and help them out of poverty. But…Americans are taxed three times for their ethanol hunger—they subsidize the growing of corn through the government; they subsidize the manufacture of ethanol; and they pay more for their food. Ethanol production actually impairs the ability of people to contribute to the demand for manufactured goods.

In order to produce fuel ethanol, a farmer must use fuel for his tractors, petrochemical fertilizers and pesticides, truck fuel, and distillation fuel. So…on balance, it takes just about as much fuel to produce the new ethanol fuel as the ethanol fuel, itself contains. Drilling and refining fuel from oil and coal reserves, of which there are many, gets you a 600% energy return on your energy used.

Making fuel from Brazilian sugar cane is more efficient, because it is produced by armies of underpaid laborers.

Using oil to drive cars releases CO2, which is a greenhouse gas; but using tractors to grow crops releases nitrous oxide from soil, which is a stronger greenhouse gas with nearly 300 times the warming potential of CO2.

The ultimate argument against the use of biofuels is that these fuels require land for their production; and the earth’s land area is finite. The human population, which uses land for food production, is increasing. By 2050, the earth’s population will need every bit of arable land for food production. We need to quit using biofuels until some more efficient way of producing them is discovered.

Data for this blog post were taken from The Rational Optimist by Matt Ridley.