The Great Global Warming Swindle UK Channel 4, March 8 20007
The Arguments
Earth's 4.5 billion year history is one
long story of climate change. This fact is pretty much accepted by those who think global warming is a natural process, and those who think it's caused by man.
In more recent history there has been: a mini ice age in the seventeenth century when the Thames froze so solidly that fairs could regularly be held on the ice; a Medieval Warm Period, even balmier than today; and sunnier still was the so-called Holocene Maximum, which was the warmest period in the last 10,000 years.
Those who think global warming is a natural process point to the fact that in the last 10,000 years, the warmest periods have happened well before humans started to produce large amounts of carbon dioxide.
A detailed look at recent climate change reveals that the temperature rose prior to 1940 but unexpectedly dropped in the post-war economic boom, when carbon dioxide emissions rose dramatically.
There is some evidence to suggest that the rise in carbon dioxide lags behind the temperature rise by 800 years and therefore can't be the cause of it.
In the greenhouse model of global warming, heat from the sun's rays is trapped by greenhouse gases in the atmosphere. If it weren't for these gases, Earth would be too cold for life.
Greenhouse gases trap heat from the sun within the earth's atmosphere. This is the greenhouse effect. Traditional models predict that increasing concentrations of
greenhouse gases lead to runaway heating.
If greenhouse warming were happening, then scientists predict that the troposphere (the layer of the earth's atmosphere roughly 10-15km above us) should heat up faster than the surface of the planet, but data collected from satellites and weather balloons doesn't seem to support this.
Those who think global warming is a natural process say that the troposphere is not heating up because man-made greenhouse gases are not causing the planet to heat up.
For some people, the final nail in the coffin of human-produced greenhouse gas theories is the fact that carbon dioxide is produced in far larger quantities by many natural means: human emissions are miniscule in comparison. Volcanic emissions and carbon dioxide from animals, bacteria, decaying vegetation and the ocean outweigh our own production several times over.
Others would argue that carbon dioxide isn't the only greenhouse gas and that human emissions could tip up a finely balanced system.
New evidence shows that that as the radiation coming from the sun varies (and sun-spot activity is one way of monitoring this) the earth seems to heat up or cool down. Solar activity very precisely matches the plot of temperature change over the last 100 years. It correlates well with the anomalous post-war temperature dip, when global carbon dioxide levels were rising.
In fact, what is known of solar activity over the last several hundred years correlates very well with temperature. This is what some scientists are beginning to believe causes climate change. Others feel that solar activity only explains the fine details of temperature change.
So how does the sun affect the earth's temperature? The process scientists suggest is that as earth moves through space, the atmosphere is constantly bombarded by ever-present cosmic rays. As these particles hit water vapour evaporating from the oceans, clouds form in the atmosphere. Clouds shield Earth from some of the sun's radiation and have a cooling effect.
When solar activity is high, there is an increase in solar wind and this has the effect of reducing the amount of cosmic radiation which reaches Earth.
When less cosmic radiation reaches Earth, fewer clouds form and the full effects of the sun's radiation heats the planet.
But is the effect of solar activity really enough to explain away global warming caused by the greenhouse effect? This is still a moot point – have your
vote here.
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