My previous blog articles for Bookboon so far have been mainly inspired by freaky weather. I have not really talked about “moisture”, the driving force behind these events. In this article for the Bookboon blog, I explain the link between my eBook A Wet Look At Climate Change (AWLACC), moisture and the various moisture-related topics I have written about since publishing AWLACC. 


First, let’s begin with the structure of my eBook AWLACC:

The first three chapters provide background technical information on the way moisture behaves. Chapter 1 covers a physical property that you will all be familiar with Relative Humidity (%RH). Without using mathematical terminology I provide an explanation of %RH, which is absolutely fundamental to gaining an understanding of the way moisture behaves in the world around us.

In Chapter 2 the %RH theme is taken further to appreciate the importance of the meaning of “Saturation” when we are talking about moisture in the air. To complete our introduction to the world of moisture, in Chapter 3 the subject covered is called Equilibrium Relative Humidity (ERH). For me, this was the most difficult concept to get my head around, and having presented at meetings and conferences, a difficult topic for most people as well. It is also known as Water Activity and is the driving force for most of the effects of moisture that I write about and we see all around us.
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All the other chapters in AWLACC draw on these principles of %RH, Saturation and ERH to give insights, or better still, to explain how moisture behaves to change or influence the world around us. Remember that moisture is simply water in the air that we see as steam from a kettle or clouds in the sky. But water in the air does not behave simply. Just as Brian Cox in BBC’s Forces of Nature pointed out, water is a simple molecule “just two hydrogen atoms and an oxygen atom stuck together” but each water molecule interacts with other water molecules in a very complex way to be this amazing substance essential for life.

To show you how the information in my introductory chapters in AWLACC can be used to get a better understanding of moisture, here’s an example from my moisture-matters blog:  You say biscuit, I say cake! In this article about one of my favorite “biscuits”, Jaffa Cakes, I relate a story that involved a very long legal dispute between McVitie’s and the Inland Revenue over VAT. If a product is a biscuit, there is no VAT. But if it is a cake, then VAT is paid. Whether Jaffa Cakes are a biscuit or a cake came down to them becoming moist and soft in normal room conditions, or dry out ending up hard. This happens because the ERH (Chapter 3) of the Jaffa Cakes is rather above or below the %RH (Chapter 1) of the room, and that drives moisture in or out of the “biscuits”. Who do you think won the court case?

More of my articles on individual topics about moisture can be found at


More interesting articles by Peter Moir on moisture and climate change:

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