What are the main sources of greenhouse gases?
What are the main sources of greenhouse gasses?
There is a unanimous scientific consensus around the world that the rapid global warming we have experienced since 1800 is due to the accumulation of greenhouse gasses in the atmosphere as a result of human activity [1]. The main greenhouse gasses are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Emissions of carbon dioxide are largely caused by the combustion of fossil fuels like coal, oil, gas and petrol and form by far the greatest proportion of greenhouse gasses. Methane is the next largest contributor and the main source is livestock farming, while nitrous oxide is mostly produced by the fertilisers used in modern agriculture, and is the smallest contributor to global warming of the three main greenhouse gasses.
The graph shows that the USA and Europe (including the UK) are responsible for a whopping 62% of all the CO2 in the atmosphere. On the other hand, countries like China, India and Japan combined account for 20%, whilst Afrika and South America combined account for only 6%. This shows that most of the responsibility for the global warming that has occurred so far is down to the USA and Europe, and that these countries therefore have the greater duty to take the strongest measures.
On the other hand, if we look at the biggest annual sources of greenhouse gas emissions today, we get a very different picture. The graph below shows the total CO2e annual emissions of each country around the world. Suddenly you can see that the biggest annual emitter of greenhouse gasses today is China, with the USA in second place. In fact, China, the USA and Europe (excluding Russia) combined now account for nearly 50% of all greenhouse gasses emitted globally each year.
Another way to consider where the main sources of greenhouse gasses come from is to break up global emissions into sectors such as agriculture, finance, heating, and so on, and calculate the amount of emissions each sector produces. This kind of analysis treats the whole world as a single country and breaks down greenhouse gas emissions into sectors for the global economy.
The graph below shows one such analysis for the global economy in 2020 across all greenhouse gasses (CO2e). You can see that electricity and heating, along with agriculture, account for nearly 50% of all greenhouse gas emissions. Transportation, such as cars and lorries, along with industry, such as steel making, also account for a significant share of the global total. This shows that if we can make our industries more efficient and less carbon intensive (often referred to as 'decarbonising'), switch our electricity sources to renewables and our heating to heat pumps, drive a lot less, and change our diet away from meat, then we would be making a huge contribution to tackle global warming.
Not all greenhouse gasses are the same when it comes to their warming potential. Methane, for example, has a warming effect on the atmosphere 85 times more powerful than CO2 over a 20 year time period, but CO2 remains in the atmosphere for 100 years while methane only lasts a decade. This means they are difficult to compare when analysing the sources of greenhouse gasses, and for this reason the contributions of other gasses such as methane and nitrous oxide are often converted into a carbon dioxide equivalent (CO2e) so that they can all be compared on one graph.
The Main Global Sources of Greenhouse Gasses
There are lots of different ways to answer the question of where the main sources of greenhouse gasses come from. First off, you can consider which countries have produced the most greenhouse gas emissions since the beginning of the industrial era. The first graph below shows the total amount of carbon dioxide produced by many countries since 1790 (it does not include the other greenhouse gasses).
But yet another perspective is offered when you look at the annual per capita emissions of greenhouse gasses by country. In this case, the annual emissions of each country has been divided by the population of that country, so that you get a more balanced figure which reflects the greenhouse gasses emitted by that country per person. The graph below (which only shows the figures for CO2 and not CO2e) shows the per capita emissions of CO2 per country. In this case, you get countries like Qatar and Saudi Arabia who have huge per capita emissions, but because they are small countries, they don't contribute much overall and so don't figure on the graphs above. The United States, on the other hand, remains a large contributor no matter how you look at it, whilst China, due to its large population, suddenly looks a lot smaller.
Another perspective on the sources of greenhouse gas emissions is to look at the greenhouse gas emissions caused by an individual's everyday activities, often referred to as a carbon footprint. The figure below shows the carbon footprint for the average person in the UK. It shows that roughly one quarter of the greenhouse gas emissions that the average individual causes results from activities related to the home, such as heating or electricity use, while the food we buy amounts to around 40%. This kind of simple graph can be useful for pinpointing the main areas to focus on behaviour change if we want to adapt our lives to a low carbon ethos.