Put simply: What are greenhouse gases and how do they cause global warming?

Let’s start with a conundrum: even the least scientific amongst us know that the sun is very very hot (about 5,500^oc). But outer space, between us and the sun, is very very cold (about minus 270^oc). So how can we feel the heat from the sun if the bit in-between is so cold?

The answer lies in the different types of energy. The sun’s rays travel across space as a form of energy known as ultraviolet. That’s why your suntan lotion refers to protection from UVA and UVB – the UV standing for ultraviolet. However, ultraviolet is unable to carry heat. Which is why, despite the sun’s rays travelling through space, it remains so cold. 

But when ultraviolet hits a solid object, some of it is absorbed and re-emitted as a different type of energy – known as infrared. And this is heat. The darker the object, the more of the UV that is absorbed and re-emitted as heat. You have no doubt experienced this without realising. Ever been walking along on a scorching hot summer’s day when your sandals break and been forced to carry on barefoot? You learn very quickly to avoid stepping on anything dark (ouch!) and to seek out paler surfaces (phew!). Well this is the process in action. The darker surfaces absorb more UV, emitting infrared and turning very hot, whereas most of the UV bounces straight off those paler surfaces which remain cool. 

Ever stood on a mountain top surrounded by snow, sunlight blinding your eyes and warming your face, and wondered why the snow around you is not melting? Same thing. The UV is bouncing off the white snow but being absorbed on your skin and turning into heat on the surface. It’s all a trick. We don’t directly feel the heat from the sun in the same way we do coming off a fire – it’s the UV turning to infrared on your skin and clothes that we can feel.

So what has this got to do with a greenhouse? Well quite simply it’s how a greenhouse works. UV rays from the sun pass through the panes of glass on a greenhouse, get absorbed by the dark soil inside, and re-emitted as infrared heat. However, unlike UV, infrared energy cannot pass through glass. So the infrared heat emitted from the soil is trapped inside the greenhouse, and it becomes warmer inside than out.

So finally we have the answer to our question! Greenhouse gases are quite simply gases that behave in exactly the same way that a greenhouse does – or more strictly speaking, like the panes of glass on the greenhouse. They allow the sun’s rays in the form of UV to pass through, but then prevent any infrared heat emitted from the earth’s surface from escaping back into space. The more these gases build up in the atmosphere, the more heat is trapped, and the hotter our planet becomes. 

Now there are lots of different greenhouse gases and they are not all equal in relation to how much global warming they cause. Think of it a little like the difference between putting on a cotton t-shirt versus a thick woolly jumper. The latter is going to warm you up a lot more than the former – ask a sheep. The most common greenhouse gas is carbon dioxide which we emit, for example, when breathing, or when burning fossil fuels such as coal, gas or petrol (that’s gasoline to any Americans!). The second most common is methane (natural gas), which can be emitted directly from leaks in gas infrastructure such as pipelines, as well as from agriculture, rotting vegetation – and yes, as commonly cited, from cow’s farting. I can’t resist at this point quoting my lovely parents. When he heard about methane from cow’s farting my father said “could you not just stick a cork up there ?!!” –  to which my mother retorted “well no, because then they’d just start burping!”. Brilliant.

Apologies, cough, back to the science.

So in summary there are different types and sources of greenhouse gases, and the amount of warming caused by these gases – known as global warming potential – varies. For example, one tonne of methane is equivalent to about 28 tonnes of carbon dioxide in terms of the amount of global warming that it causes over a 100-year period. Nitrous oxide, is another greenhouse gas, emitted from soils, agriculture and industrial processes. But it is around 265 times more potent per tonne than carbon dioxide. Indeed some greenhouse gases can be many thousands of times more potent.

So if other gases are worse, then why do we tend to focus on carbon emissions (or emissions from carbon dioxide (CO2) and methane (CH4) which both contain carbon). Well the answer lies in the relative amounts of each greenhouse gas. A particular gas may cause significantly more global warming per tonne, but there may be very little of it, so it isn’t as big a concern. The same way that despite arsenic often being naturally occurrent in apples, it doesn’t concern us as it is typically only present in tiny trace amounts – thank goodness.

So how do we measure the relative amount and impact of different greenhouse gases? 

Let’s continue with a simple analogy. Many people reading this will no doubt have one of those boxes or tins containing a few notes and coins in different currencies left over from past holidays and trips – dollars, euros, sterling, yen etc. If asked how much money there is in total,  how would they answer? Most likely they would convert everything to one currency using different conversion rates. For example: “I have the equivalent of 24 dollars.” 

Well we do the same for greenhouse gases. We convert everything into their carbon dioxide equivalent (CO2e) using the relative impact they have on global warming. That is the global warming potentials mentioned above. So every tonne of carbon dioxide is obviously one tonne of carbon dioxide equivalent (1t CO2e), whereas a tonne of methane is multiplied by its global warming potential to become approx. 28tCO2e, and one tonne of nitrous oxide becomes approx. 265tCO2e and so on.

When you convert all of the greenhouse gases to CO2e in this way, and add them all together, then you discover that about three quarters (75%) of all greenhouse gases emitted globally each year are made up of carbon dioxide and around 15% of methane. And that is why policy tends to focus on reducing carbon emissions. But in sectors where they are emitted it is even more important to stop release of the more potent greenhouse gases. 

So there you have it. Greenhouse gases are gases that behave like the panes of a glass in a greenhouse, allowing UV rays through and preventing infra-red heat emitted by the earth’s surfaces from escaping back into space – resulting in global warming. 

©August 2025, Waterlilly.blog