What are Greenhouse Gases?

On the surface, the answer to the question ‘What are Greenhouse Gases?’ may seem fairly obvious but the reality is more complicated than you might first imagine. 

A broad definition is that greenhouse gases (GHGs) behave like the glass panels of a greenhouse, letting heat into the atmosphere but not allowing it to escape – giving them the name greenhouse gases. However, from a purely natural perspective, without that greenhouse effect, global temperatures would probably drop to about minus 20°C, according to the British Geological Survey, which is too cold to sustain most life on earth.  

But activities that humans undertake have and increasingly are changing the natural greenhouse effect on Earth with a significant rise in the release of GHGs, which it is generally agreed are the cause of global warming and climate change.  

An ongoing temperature analysis conducted by scientists at NASA’s Goddard Institute for Space Studies (GISS), reveals the average global temperature has risen by at least 1.1°C since 1880. The majority of this warming has happened since 1975, at a rate of around 0.15°C to 0.20°C per decade. 

Yet what are the GHGs that are causing this increase? The GHG Protocol is the most widely accepted method for companies to account for greenhouse gas emissions. The GHG inventory covers seven direct greenhouse gases under the Kyoto Protocol as follows: 

Carbon dioxide (CO2) 
Methane (CH4) 
Nitrous oxide (N2O) 
Hydrofluorocarbons (HFCs) 
Perfluorocarbons (PFCs) 
Sulphur hexafluoride (SF6) 
Nitrogen trifluoride (NF3) 
Although water vapour is the most abundant GHG and its level increases as the Earth's atmosphere warms, it is unlike CO2, which can remain in the atmosphere for centuries, whereas water vapour persists for a few days. 

The atmospheric CO2 concentration has risen by 47% since the Industrial Revolution began in the 1800s, according to a report by NASA. That is due to human activities such as the burning of fossil fuels and large scale deforestation among other things. Because of its abundance, CO2 is the main contributor to climate change. 

Methane, on the other hand, is produced naturally through decomposition. However, human activity has upset the natural balance. A very large amount of methane is released by cattle farming, landfill waste dumps, rice farming and the traditional production of oil and gas. Nitrous oxide, meanwhile, is produced through the large scale use of commercial and organic fertilisers, burning fossil fuels, nitric-acid production and biomass burning, among other things. 

How are GHGs Measured? 

GHG emissions are often measured in carbon dioxide equivalent, abbreviated to CO2e. It is a measure used to compare the emissions from various GHGs on the basis of their global warming potential (GWP), which is a term used to describe the relative potency, molecule for molecule, of a GHG, taking account of how long it remains active in the atmosphere. 
To quantify CO2e, you have to multiply the amount of the greenhouse gases by their GWP. The GHP IPCC GWP for methane, for instance, is 28 and for nitrous oxide 265. This means that emissions of 1 tonne of methane and nitrous oxide, respectively, is equivalent to emissions of 28 and 265 tonnes of carbon dioxide.  
Usually, GWPs are calculated over a 100-year timeframe but there are a number of other metrics that could be used for comparing one GHG to another. For example, the 20-year GWP is sometimes used. This GWP prioritises gases with shorter lifetimes because it does not take into account impacts that happen more than 20 years after the emissions occur. Because all GWPs are calculated relative to CO2, GWPs based on a shorter timeframe will be larger for gases with lifetimes shorter than that of CO2, and smaller for gases with lifetimes longer than CO2.  
Another alternative metric is the Global Temperature Potential (GTP). The calculation of this is more complicated than for the GWPs, because it relies on modelling how much the climate system responds to increased concentrations of GHGs (the climate sensitivity) and how quickly the system responds (based in part on how the ocean absorbs heat). 
More information on the above can be found here


Where do GHG Emissions Come From? 

Trying to account for all of the greenhouse gases around the world is a major undertaking and it’s not just CO2: there’s methane, ozone, refrigerants, and a variety of other gases and particles that all add to warming the planet, and all of which are tracked by the IPCC. The chart below helps to illustrate the causes: 

Where do Greenhouse Gases come from?Where do Greenhouse Gases come from?

As the chart shows, electricity and heat from powerplants and other industrial sources produced by burning coal, natural gas and other fossil fuels for industry is the largest source of greenhouse gas emissions worldwide. This is followed by agriculture and land - mainly from emissions from livestock. However, it also includes fuel used for agriculture, forestry and fishing, direct soil emissions and forest fires.

Perhaps the most obvious source of emissions comes from transportation. But we don’t notice all of it: aviation, rail and refrigeration in transport, for instance, all contribute to output from transportation, adding around 14% of GHG emissions, according to the chart above. 

Meanwhile, energy used in commercial and residential buildings, including refrigeration and air conditioning, and even fire extinguishers, contributes 6.4% of global emissions.  
Of them all, perhaps the most surprising is food waste. That contributes 6.7% of global emissions. It starts well before it leaves the farm and continues through distribution, storage, at markets and restaurants, and all the way to your kitchen – and all too often, into the bin. More on the subject here. 

So, in response to the question: ‘Where do GHGs come from,’ a perfectly reasonable answer is: ‘A lot of places - it’s complicated.’ 

Overall, there is little doubt that the accumulation of GHGs is probably the biggest threat we have ever faced. Knowing what GHGs are and where they come from is a small step in arming ourselves with the tools to try to mitigate what will be, if left unchallenged on a global scale, a disastrous outcome. 

Here at Techbuyer we believe the issue of GHGs, what we call the carbon conversation, cannot be put off; everyone needs to be open to learning more, finding solutions and reconsidering our emissions for a sustainable future.  

This piece is part of our series designed to offer digestible information, thought-provoking discussions and sustainable solutions for having the carbon conversation and working as a collective to reduce our environmental impact on the planet.  

Get in touch to start your carbon conversation.  

Learn more about key definitions on core carbon topics, such as life cycle assessment, carbon neutrality and net zero, embodied carbon and Scope 3 below. 

Let’s have a carbon conversation. 
For further reading, visit: 

What are Scope 3 Emissions? 

What is Embodied Carbon? 

What is a Life Cycle Assessment? 

Carbon Neutrality vs Net Zero/What is the Difference? 

Carbon Considerations and the Circular Economy