The Temperature Record

Planet Earth has experienced a general trend of warming which appears to coincide with the industrial revolution, and the dramatic increase in the level of man-made carbon dioxide emissions that industry produces. Is carbon dioxide causing the temperature to increase? Or is the temperature increasing naturally?

To answer this question, we must first of all ask a more basic question: is the recent warming trend "unnatural"? Let's look at the temperature of the Earth over the last 10,000 years:

From this graph it can be seen that the Earth has been both warmer and cooler than it is today; we are well within the normal temperature range.

The warming trend out of the last great ice age, around 10,000 years ago, permitted the development of the first agrarian societies. Since then, the temperature has kept within a relatively small range.

Let's take a closer look at the last 1000 years.

Here we can see that, even within this narrower span of time, the Earth has been both warmer and cooler than it is today. The current warming trend appears to be a recovery from a particularly cold period, known as the Little Ice Age.

The temperature of the Earth today is not at all unusual. It was hotter than it is today during the Medieval Warm Period.

There is no reason, based on the historical data, to suspect that humans are having a "catastrophic" effect on climate.

There is, as Al Gore points out, a close correlation between carbon dioxide and temperature. This is used by Gore and many proponents of the man-made global warming theory as evidence that carbon dioxide must be causing temperature change. But there is an alternative: what if temperature causes changes in the level of carbon dioxide?

How can we tell which way round it happens? The most obvious way, since a cause must always come before an effect, is to ask whether the temperature changes or the carbon dioxide level changes come first. The answer, based on the exact same data used by Gore to demonstrate the correlation, ice-core samples, is that temperature changes come first, followed by changes in the level of carbon dioxide. While the "lag" is not apparent in Gore's large-scale graph, it is much more noticeable when the graphs are put together and closely examined. The magnitude of the "lag" is about 800 years.

This shows that carbon dioxide has not been the driver of climate change in the past.

But could it be that, without human carbon dioxide emissions, the Earth would now be colder, not yet recovered from the Little Ice Age? Let's have a closer look at the period in question - the last 120 years.

This period is when human beings started producing an increased amount of carbon dioxide; the amount of carbon dioxide released during this period is an exponential increase.

What does this graph suggest? Well, there is a noticeable period in which the temperature of the Earth decreased - for about 35 years from 1940 to 1975. This includes the "post-war economic boom" where human carbon dioxide emissions dramatically increased.

If carbon dioxide is responsible for global warming, how can it be that the Earth was getting colder during these years?

The UN International Panel on Climate Change (IPCC) has been forced to change it's theory due to its incompatibility with the reverse correlation between temperature and climate change observed between 1940 and 1975. Rather than abandoning the theory altogether, it now asserts only that the warming post-1975 is due to increased carbon dioxide emissions.