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Several years of talking to people about climate change means that I have come across my fair share of people who don't believe that there is such a thing as human induced climate change; that this is all in fact just one of many natural cycles the earth goes through. For the most part, they fall back on to one of several arguments to demonstrate their point.
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.
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.