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  • Graham Harris

What is a greenhouse gas? Or, why climate change and bread have more in common than you think.

I don’t like to make assumptions. While climate change has received a lot of media attention over the last couple of decades, I still don’t think it’s wise to assume that everyone is familiar with the basics. The most basic of which is understanding greenhouse gases and their role in the climate change story. So, for my first blog post, that’s where I decided to start.

So, what is a greenhouse gas? Simply put, it’s a gas that traps heat from the sun, much like the panes of glass in a greenhouse…hence their name. Our world receives heat from the Sun and loses heat to space. Greenhouse gases regulate this exchange and create the heat balance of our atmosphere; and while greenhouse gases are usually cast as the villain in any climate change story, without them we’d be living (or not) on a very cold planet indeed, for the word ‘balance’ in my prior sentence is key. Thus, when it comes to climate change, the problem isn’t greenhouse gases per se (or GHGs, to give them their common abbreviation and save my fingers some typing stamina); the problem is how much of them we are currently releasing into the atmosphere, as more GHGs means more heat being trapped.

OK, but let’s return to our high school chemistry. If you remember, you probably learned that the vast majority of our atmosphere is made up of only two gases: Nitrogen (N2), which makes up the bulk of it, at around 78%; and Oxygen (O2), which makes up another 21%. All the other gases thus make up only 1%. Of these, the prevalent GHG in our atmosphere is carbon dioxide (CO2) – which makes up around 0.04% of our atmosphere, according to NASA. CO2 naturally comes from animals (like us) as they breathe and is taken up by plants and trees. CO2 is also a by-product of combustion – so forest fires and volcanic activity are also natural contributors. Four one-hundredths of a percent doesn’t seem like a lot, does it? How can CO2 possibly be so important?

Well, bear with me as I talk about bread (I love bread) – specifically, the kind you bake with yeast. A good baguette, ciabatta, or even a simple white or whole-wheat loaf depends on gas for its wonderful, fluffy texture; the gas in question being the CO­2 that is released by the yeast as it breathes. But it needs the right amount of gas; if there’s too much, the bread will over-rise (or ‘over-proof’) and will ultimately collapse; conversely, if there’s too little, the bread won’t rise enough and you’ll be chewing on a slab instead of a nice baguette…in other words, the amount of gas is critical to the balance of the chemistry upon which bread-making depends. You don’t need a lot of yeast in a loaf – around 15g in in a mix of ingredients (flour, sugar, salt, water and yeast) that collectively weighs around 1000g, or 0.015% (based on this basic bread recipe, which I use a lot, if you are interested). So, not a lot. But too much or too little leads to a baking catastrophe.

Now carry this analogy over to our atmospheric discussion. Remember that CO2 is a by-product of combustion. Since the industrial revolution – which has been literally fuelled by the combustion of “fossil fuels” (coal, oil, natural gas, etc) – we have been pumping out mind-boggling volumes of CO2 (as well as methane and nitrous oxide, other combustion by-products which are even more potent GHGs) into the atmosphere. This is affecting the natural heat balance. Concentrations of carbon dioxide (CO2) have risen by 40% since 1750 and “atmospheric concentrations of GHGs are at levels that are unprecedented in at least 800,000 years.” (so say the IPCC). The result has been a fantastically quick (in geological and evolutionary terms) shift in the amount of heat being trapped in our atmosphere, such that our planet is actually warming up.

Now, you may not feel any warmer, and overall, life as you know it probably isn’t that different than it was 10 years ago. But changes have been happening, and the impacts of those changes are being felt worldwide (and that’s a subject for another time).

So, in summary, what is a GHG and why do they matter? GHGs trap heat. More GHGs = more heat. Over the last 250+ years we’ve been gradually increasing the amount of yeast in our bread recipe; so far, our bread keeps turning out fine, so many people just don't see the problem. But while we may not be sure of the exact amount of yeast that will produce too much gas and trigger a collapse, we do know that the structure is under stress and that we will reach that point eventually.

Something for us all to think about over our morning toast.

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1 Comment

James Bererton
James Bererton
Jan 24, 2020

Really well written; interesting comparison with the small amount of yeast and the potential to collapse the bread.

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