The Hot Air of Climate Change, Part 2

This is a multi-part series examining the current debate over "global warming", also known as "climate change".

In our look at the subject of global warming, we've seen that it's not possible at our present date and time to prove that the Earth is warming in the first place.  But let's lay that aside, and assume that it's true - Earth is getting warmer.  The next question, then, must be:

2. Is this change part of a known natural cycle?

It's long been known that global weather patterns have cyclical changes.  Some of these cycles are short - the famous El Nino conditions occur every 2 to 7 years, and last a year or two.  Some of these cycles are very long.  We seem to get major ice ages at intervals of hundreds of millions of years. There are thousands of cycles, local and global, lying between these two extremes, some of which are known and have been documented, others of which are yet to be discovered.

Even in historical times, there have been quite significant changes in temperature.  Western Europe experienced a general cooling of temperatures during the late Middle Ages, and a generally much colder climate between 1560 and 1850.

During this time, London's Thames River regularly froze over, so much so that Londoners held "Frost Fairs" out on the ice, as is done today in much-colder Montreal.  There have been no Frost Fairs in London since 1814, so clearly the weather there has gotten warmer since then.

But further back in the past, it was quite a lot warmer.  During the Medieval Warm Period, from 850 until around 1250, there were extensive vineyards in England, with wine production sufficient to challenge the French in the markets; you don't see this even today.

This was also the time when the Vikings colonized Greenland.  As has been well documented, the Vikings tried to establish a standing civilization on what was already rather marginal land, at a time when the climate was about to trend much, much cooler; Jared Diamond has a moving description of how the Little Ice Age brought civilization in Greenland to an unhappy end in his book Collapse.

Over time, it's been both much colder and a good bit warmer than it is today.  It's been reported that the hottest years of the past century was 2006 until NASA found their math was wrong: it was actually 1934.  This certainly illustrates the previous point made - it is very, very difficult to actually measure the changing temperature of the Earth in a globally meaningful and useful way, but also underscores the fact that today's temperatures are certainly within historical ranges.  The temperature and weather patterns we see today are not out of the ordinary, nor are the trends associated with them.

But because of the complexity of global weather cycles, it is not really possible to know for sure that that's all we're seeing.  There could be more involved.  So let's move on to the next question:

3. If not simply part of a normal climactic cycle, what is causing the change?

To be continued...