Anomalies in Climate Change Mean Temperatures

An anomaly is an easy thing to define because it is simply a deviation from the norm, but a hard thing to identify because it is so hard to understand what is “normal”. In climate science there are masses of deviations from the norm, for example most glaciers are shrinking but some are growing. In fact there are so many anomalies that sometimes it can be hard to understand what the norm is. What is a global warming norm?  

As far as we can see (and we cannot see very far) global mean temperatures were more or less steady from 2000 BC until about 1000 AD. There were year to year and decade to decade anomalies within those that period of three thousand years. There was then a little bit of warming followed by a little bit of cooling and then the mean fell to levels that were previously mean temperature levels. Then, co-incidental with the industrial revolution mean temperatures rose relatively very rapidly to higher levels than had been experienced in the past four thousand years.

Which is the anomaly? The year to year mean fluctuations, or the decadal fluctuations or the medieval warm period or the medieval cool period or the post industrial revolution warming or the fact that in the past ten years global mean temperatures have only risen by 0.14°C?

Calculating a mean global temperature today is only possible to approximate standards. Not every part of the earth has temperature measuring equipment; many parts have no equipment and we cannot collect any data at all from these parts; many measurements have not been recorded for more than 100 years. Much of the temperature recording equipment in the past has been incorrectly installed, poor calibrated so we can only see the picture painted with a broad brush, an example of which are the NASA measurements which you cans see at http://data.giss.nasa.gov/gistemp/graphs_v3/

There is also the time frame we chose, which gives us different ideas about global warming impacts in different parts of the world.

Of course anomalies fuel debate; you can pick a set of statistics and argue almost anything from them. Perhaps the most common error is to think that there is an absolute global mean temperature at all. If there is one, we cannot calculate it, but what we can calculate are the anomalies themselves, they are the basis of climate science and global warming warnings, From the anomalies we can see trends. They have to use land temperature measurements, sea temperature measurements and air temperature measurements, all at different levels above and below the sea.

So perhaps it is best to stand back, as far as you can to look at the picture painted with a very broad brush indeed and know that the painting is incomplete. Then use your instincts and perception to reach a view.

My view is that the plant is warming rapidly but in the past ten years the warming has been mostly conducted to the sea and the Arctic region, but that warming has not yet showed up in the global mean temperature measurements because of insufficient data coverage.

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