“Know your numbers” is a fundamental precept of business – Bill Gates
It is common knowledge that Russia is the largest country in the world. But how large?
The answer is 17.1 million km² . But even with this information are you any wiser?
Without external benchmarks or other numbers to compare it against then it is difficult to quickly comprehend this solitary number.
With some extra information ’17 million km²’ can make sense. For example, Canada, China, and the US all have surface areas of between 9-10 million km². Now, armed with that extra information you are better able to appreciate that Russia is a very large country, nearly double its closest rivals.
Applying Numbers to Emissions
In many ways greenhouse gas emissions represent a similar challenge.
It is common knowledge that some governments and organisations are targeting emission reductions that achieve ‘net-zero’ by 2050 (or sooner) in order to limit global temperature rises to 1.5-2℃, but how much emissions are we producing today? How much carbon is already in the atmosphere?
Armed with these small nuggets of information you will be able to better appreciate emissions data presented in climate analysis, news, scientific papers, or media reports. And crucially judge whether they are meaningful or not.
Units of Greenhouse Gas Emissions – MtCO2 and MtCO2e
Emissions of CO2 are measured in MtCO2, which simply refers to ‘metric tonnes’ of CO2. However, carbon dioxide is not the only greenhouse gas and if we want to take into account the effect of all these other gases then the total GHG emissions are measured in MtCO2e, which reads as ‘metric tonnes of CO2 equivalent’:
A metric tonne is simply 1000kg. But be aware that ‘Mt’ can also mean megatonnes or a million tonnes. The easiest way to judge if it is ‘metric tonnes’ or ‘million tonnes’ is context and scale. National or industry emissions will be in millions of tonnes, emissions on the level of an individual will usually be in metric tonnes. But if you are unsure delve a little deeper.
Another common unit is GtCO2, which refers to gigatonnes or a billion tonnes.
‘CO2 equivalent’ is a bit more complex, as it includes both carbon dioxide and other greenhouse gases, such as methane, nitrous oxide, and sulphur hexafluoride. Some greenhouse gases will cause more global warming than others and this can be measured relative to carbon dioxide.
For example, methane has 28 times the warming impact of carbon dioxide (when measured over 100 years ); so if every CO2 molecule emitted was a methane molecule, then global warming would be approximately 28 times worse.
Therefore to take into account all the different GHGs the warming effect is calculated relative to CO2. Then the masses of each GHG are scaled relative to their warming effect before the total warming effects of these gases (plus CO2) are added together.
Current Global Annual GHG Emissions
Let’s start with the basics, in 2018 the total global CO2 emissions due to human activity was 37.1 GtCO2 (gigatonnes or billion tonnes) . As a historical comparison, in 1900 emissions were 1 GtCO2, in 1950 emissions were 5 GtCO2, and in 2000 emissions were 25 GtCO2.
If we include all other GHG emissions (CO2 + other GHGs) then the total global emissions increases to 51.8 GtCO2e in 2018 . From this data you can see that CO2 easily makes up the majority of GHGs.
Annual CO2 Emissions Per Capita
In 2017 the average CO2 emissions per person was 4.8 tonnes .
However, this overall figure disguises a huge difference between countries, with emissions per person ranging 49 tonnes in Qatar to 0.06 tonnes in the Democratic Republic of Congo.
Of the larger world economies, per capita CO2 emissions are:
- Australia, US and Canada are around 16 tonnes per person;
- Japan is at 9.5 tonnes per person;
- Western Europe is between 6-9 tonnes per person;
- China is 7 tonnes per person;
- India is just under 2 tonnes per person.
How Much CO2 is Stored On Earth And Where?
Our planet has a complex carbon carbon cycle, whereby carbon is transferred between natural carbon stores or sinks. Land use changes, human industrial activity, and man-made carbon dioxide are upsetting this cycle and it is important to quantitatively understand how global emissions fit into the wider picture. First we must understand where on earth carbon is stored :
- Atmosphere: 3,000 GtCO2
- Oceans: 150,000 GtCO2
- Organic Matter On Land: 15,000 GtCO2
A Focus on Atmospheric CO2
Although the atmosphere may appear to contain relatively less CO2 when compared to the oceans and organic matter on land, the atmosphere contains significantly more CO2 than before the industrial revolution and the mass burning of fossil fuels.
The pre-industrial atmosphere contained 2,100 GtCO2. Therefore, 900 GtCO2 out of the 3,000 GtCO2 are from anthropogenic sources (i.e. man-made).
Since the start of the industrial revolution man-made emissions have totalled 1,500 GtCO2, therefore 600 GtCO2 (i.e. 1,500 GtCO2 – 900 GtCO2) has been captured and stored by terrestrial and ocean sinks. But the rest is accumulating in the atmosphere.
This increase is reflected in the atmospheric CO2 concentration, which has increased 40% from 280ppm to 412ppm . ‘ppm’ refers to parts per million, therefore every million molecules 410 of in the atmosphere are molecules of CO2.
It’s safe to say that the majority of people are aware of climate change in one way or another. But delve any deeper and the level of understanding varies significantly.
By providing a few numerical waymarkers, emissions and climate-related data can be quickly understood. This is not because the numbers themselves are important but because it allows you to contextualise new information.
If a news report states a new carbon capture method can remove 2 GtCO2 per year . Then armed with the knowledge that human CO2 emissions are just under 40 GtCO2, then you can quickly assess that method. A 5% per year CO2 emissions reduction is quite significant.
The numbers described above are one key tool in evaluating the information surrounding climate change as well as the effectiveness of different methods to reduce its impact.
See more information on the numbers surrounding carbon emissions see Our World In Data.
- The Royal Society, Greenhouse Gas Removal, 2018
- Beerling, D.J., Kantzas, E.P., Lomas, M.R. et al. Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature 583, 242–248 (2020). https://doi.org/10.1038/s41586-020-2448-9
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