Why global warming doesn’t mean next year must be warmer

One of my character flaws is (hopefully occassional) intolerance. Janet Daley is the kind of ill informed commentator that brings out my intolerance.

Rather than merely condemn her article I will try to show why what she has written is, to me, foolish (Isn’t it is foolish to write an opinion on something that one clearly knows little).

Global warming is NOT soley caused by human activity. Evidence strongly suggests human activity has had a major impact on global climate. But, there IS a natural component.

What follows is a simplification

Global warming is caused by processes operating on superimposed timescales.

On extremely long time scales (100,000 -400,000 yrs) we have changes in planetary orbits, often known as Milankovitch cycles. We don’t know a lot about these except that they occur at multiple and overlapping periodicities.

Next we have so-called Dansgaard-Oechger events. These have, according to some, a periodicity of 14500 years (other doubt the periodicity and believe they are pseudo-random).

Click for larger version 

Then there are variations in solar activity, sun-pot cycles, which have a cylce of 12 yrs. These cycles also affect the northern lights, by the way.

In the background we have different levels of volcanic activity and other events that release ash, dust etc into the atmosphere. Mt Pinatubo is a recent example. It cooled the climate by something like 0.3 degrees, global (and that is a lot of energy when you think about the global-scale). Vulcanism (and the other effects like dust storms, natrual forest fires and meteor strikes) are essentially unpredictable and highly variable.

Then we have anthropogenic influences. For the purpose of our model humans have out-competed all other species, expanding to over 5 billion creatures and maintain massive numbers of livestock, such as cattle, that are climatologically ‘inefficient’. Then we have industrialisation: a great increase in coal useage exhausting fumes into the atmosphere. I’ve expressed this as a gradually increasing trend that accelerates rapidly towards the end of our series.

When we add all these individual trends, cycles, random and sporadic events, throw in a mix of random events and processes (we on’t know everything), we get the line at the top. Difficult to interpret, but showing some cyclical behaviour and lots of medium to short term variability. BUT, crucially, because of the multiple superimposed variations, next year does not necessarily have to be warmer for global warming to be a reality. In fact, an entire decade of depressed temperatures would not necessarily mean that anthropogenic climate change is not a reality.  

Note: here we’ve assumed the amplitudes are of roughly similar magnitudes: this is not really the case.

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