To keep the planet habitable, scientists say we should limit global warming to no more than 2°C. That means that we can only let 1000 gigatonnes of CO2 (or equivalent amounts of other greenhouse gases) get into the atmosphere between 2011 and 2100.
For the sake of argument, let’s divide this amount equally between everyone on the planet. The authors of A good life for all within planetary boundaries did exactly this and found that everyone would get to emit a maximum of 1.61 tonnes of CO2 eq. per year (1 tonne CO2 eq. refers to any mixture of greenhouse gases that causes the same amount of climate warming as 1 tonne of CO2).
However, they based their calculations on a population of 7 billion people – we are actually now at 7.6 billion people and growing. World population is projected to grow to 11.2 billion by the end of this century, although estimates vary from 7.3 billion to 16.5 billion1.
What’s more, a lot of greenhouse gases have been emitted since 2011. The Guardian’s carbon countdown clock shows that we have just 749 gigatonnes of CO2 remaining in our carbon budget.
A new personal allowance can be calculated using updated numbers for population, remaining carbon budget and remaining years:
Allowance = 749 gigatonnes / (82 years * 7.6 billion people)
= 1.20 tonnes of CO2 per person per year
But what does that actually mean?
Current annual emissions per person
On average, someone living in the UK causes 12.1 tonnes of CO2 emissions per year2: ten times more than the fair maximum amount per person.
In comparison, the average citizen of the United States emits 21.2 tonnes CO2 eq. per year; in Somalia, it’s 0.1 tonnes CO2 eq.
A one-way economy flight from London to San Francisco causes 1.30 tonnes CO2 eq. (the actual amount of CO2 emitted is 0.69 tonnes, but because the emissions are made high up in the atmosphere they cause more warming, an effect known as radiative forcing3). That’s your entire annual carbon allowance burned through in under 12 hours.
If you fly first-class, the story is even worse: that same one-way flight from London to San Francisco will cause 5.21 tonnes CO2 eq.
Driving a medium-sized car for 7,900 miles (the average annual mileage in the UK4) causes 2.48 tonnes CO2 eq. The same distance by bus would cause 1.30 tonnes CO2 eq., and by train would cause 0.59 tonnes CO2 eq.
According to a study of British diets5, if you eat a lot of meat, then the food you eat in a year accounts for 2.6 tonnes CO2 eq. On the other hand, if you eat an entirely plant-based diet then your food causes emissions of 1.1 tonnes CO2 eq. per year.
I’ve summarised these emissions in the chart below: one person’s “fair share” is in orange on the top row. If you want even more details of the emissions caused by different products and activities, then I recommend the book “How Bad Are Bananas?” by Mike Berners-Lee.
Sharp future cuts
The longer that emissions stay higher than they should be, the more dramatically they will eventually have to fall. This has been illustrated particularly strikingly by climate researcher Robbie Andrew. In the figure below, you can see that if we had started to reduce global emissions in 2000, we could have reduced at a fairly gentle pace: 3% per year. As it is, 10% per year is needed. If emissions stay at today’s level for ten years, then we’ll need to cut by around 30% per year when we finally get around to it.
It can be quite shocking to see how much carbon is emitted by activities that are currently seen as perfectly normal, such as taking a long-haul flight. It’s clear that business as usual can’t continue: low-carbon alternatives need to become affordable and easy to find.
- United Nations Population Fund, World population trends
- University of Leeds (2018), A good life for all within planetary boundaries – Country comparisons
- Carbon Footprint, Flight carbon footprint calculator
- Contract hire and leasing, Annual mileage guide: Why it pays to be accurate
- Scarborough et al. (2014), Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK