There is no denying it – we live in a world with a changing climate. To put climate change into perspective, we need to be reminded of that simple fact that we learned in high school – for the past several million years, the earth has been going through a series of ice ages that blanket North America & Europe in glacial ice, sometimes 2 or 3 kilometers thick. These glacial actions wax and wane over the cycle, and each cycle has a period that is relatively ice-free, called the inter-glacial, and we are in one now. Here is a chart showing the temperature for a complete glacial cycle. It is actually a bit more than one cycle so that you are able to compare our current inter-glacial with the previous inter-glacial.
There are few things worth noting which helps put our current situation into perspective. For one thing, the previous inter-glacial was quite a bit warmer than now, for most of it, and as much as 4 degrees C warmer than present. That is quite astounding when you think about it. We are being misled into thinking that global warming is unprecedented when in actual reality, we are significantly colder than we should be.
The graph is showing us one complete cycle of an ice age so that we can understand what typically occurs. Starting at the right, and moving left, from 140 thousand years ago to 130 thousand years ago, the temperature rose from about -10C to +4C. This heralds the end of the glacial period and defines the inter-glacial. It is warm enough to melt away all the glaciers blanketing the earth, with the exception of the permanent ice cap in Antarctica and high altitude regions. We can pretty much consider any period above the -2 temperature line in the graph as the inter-glacial and anything below as the glacial. As you can see, the inter-glacial is relatively short lived and by the 120 thousand year point, the temperature has dropped below the zero line and the long slow glacial period gets underway until about the 18 thousand year point where the temperature suddenly shoots up again. The next inter-glacial, the one we are currently in, started around 12 or 14 thousand years ago.
What to make of this? Well, it should be pretty clear that our current situation is well within the envelope of temperature ranges for a typical ice age. If you take a moment to compare our current inter-glacial period with the previous three inter-glacials, it should be obvious that the warming trend we have been experiencing is very likely to continue for at least a few more thousand more years as we still have another 4 degrees of warming left just to achieve the what occurred during recent ice ages. This is not a prediction, I am just merely indicating that our current situation sits inside the range of normal behaviour for an ice age. And if it were to warm another 4 degrees, then that would also be within the normal behaviour for a typical cycle.
The other thing that should be terribly obvious at this point, is that the temperature during the last 8,000 years have been relatively stable compared to the previous 140,000 years. You will see this again in some of the other pages as we expand on the time scale in the next chapter.
It is surprisingly difficult to see a graph of modern temperature readings superimposed over temperature readings obtained from Ice Core data. But it is important to do this because we need to take our present situation into context.
Central England Temperature 1650 – 2018
Here is a graph taken from a database of actual thermometer readings taken over three centuries in Central England. Yet another perspective on climate change. Today is barely different than it was 350 years ago. Take a look at the summer temperature in 1650. 15.5? Take a look at the summer temperature today. 15.7? So how is this catastrophic? Why the alarm? How is this man-made? A slight warming trend over the long term to be sure, but just as we would expect, since we are in the midst of the warming portion of the glacial cycle. When the cooling trend starts it won’t be pleasant and it will last about 110,000 years.
TOPIC – TEMPERATURE
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