It would be easy for a bystander to take these arguments on board as scientific fact; however, each and everyone one of these arguments I have heard has actually been rejected by the vast majority of the scientific community. I’m planning to go through the biggest climate change myths over the next few months, trying to seperate the truths, the partial truths, and the outright lies. Keep in mind, that it’s not only the climate change deniers who are guilty of exageration; sometimes the advocates of climate change are just as guilty of distorting the truth to get their point across.

So, in the words of Campbell Brown, we’ll be taking a ‘No bias. No bull’ approach.

The Medieval Warm Period (MWP) is often cited as an example of a time when the earth went through a period of global warming, and temperatures escalated above their climatic averages. Usually, I’ve also heard that the average global temperature during the MWP was higher than it is today.

This is a case of a partial truth. There was indeed a Medieval Warm Period (from about 900-1300 A.D), and temperatures were indeed higher than their climatic averages for the time. However, was it global, and were the average temperatures higher than todays? Evidence suggests otherwise.

The initial research into the MWP was done using data from the North Atlantic/European region, where the effect was most clearly observable.

Northern Hemisphere Temperature Reconstruction (0-2000 A.D)

However, by looking at other regions of the world during the same time period, we can that climate patterns opposite to those occuring in the North Atlantic and European region were happening elsewhere. We have to remember that what we are faced with now, is the prospect of global climate change, not regional, so we have to look at what was happening on a global basis during the MWP.

So how warm was the Medieval Warm Period?

By looking at tree rings, and ice core sample, scientists are able to draw up an approximation of a regions climates. As temperature is a regional phenomenon, each sample can only tell us about what was happening in that region. As I mentioned earlier, the MWP is thought to have been most prominent in the Northern Hemisphere, yet even there, the warmest period during the MWP is thought to have been 0.35C cooler than the average temperature from 1970-2000.

So in conclusion?

Yes, there was a Medieval Warm Period, likely caused by natural fluctuations in the Earth’s climate (like El Nino, increased volcanic activity).

But, it was likely only regional, and even at it’s peak, still cooler than the global average temperatures we are seeing today.

The current level of global average temperature is unlike those ever witnessed by humankind, and it is still increasing. We have moved beyond natural climatic cycles, and into man-made climate change.

Instead, because of the greenhouse effect, we enjoy a relatively warm average global temperature of 14°C. But how does this work?

Virtually all of the energy that reaches the earth comes from the sun in the form of light. Most of this light is in the visible range, and is the light that we are able to see. While some of it is reflected back into space by the atmosphere, and a small portion absorbed by our atmosphere, the majority of it reaches the earth’s surface, warming the land and the ocean. The land and ocean in turn, release low temperature radiation back into the atmosphere, in a form known as infra-red (IR) radiation.

Over 99% of our atmosphere is composed of oxygen, nitrogen, and argon, but for the most part these gases do not interact with IR radiation. Fortunately for us, our atmosphere also contains small quantities of water vapour, responsible for our rains, and carbon dioxide, essential to plant life on earth. Both of these gases are able to absorb IR radiation, and trap the heat being radiated from the earth’s surface. As our atmosphere warms, it becomes excited and vibrates, emitting IR radiation in all directions, most of which again reaches the earths surface starting the process all over again.

It is this recycling of heat that we call the greenhouse effect, and is why we call water vapour and carbon dioxide (amongst others) greenhouse gases.