How many planet Earths? Big numbers and eco-footprinting

As of 2011 there are more than 7 billion of us on the planet. We are placing ever more strain on our natural resources, and this is often reported in the media using big numbers:

The Guardian reported that energy consumption in China and the US amounted to 2,200 million tons of oil equivalent, for each country, in 2009. Similarly, a recent study by the UN (reported in the Independent and others) predicted that by 2018 we will have produced a total of over 50 megatons of electronic waste globally.

Sure, these are big numbers. But what do they mean? I've worked with numbers for much of my adult life and still find it hard to get a handle on these anonymous macro-statistics. One approach is to break these big numbers down into per-person figures. Cambridge University's Professor David MacKay uses units of kilowatt hours (kWh) per day per person in his easy-to-read book on sustainable energy (freely available here). This is an intuitive choice: the kWh is a 'unit' of energy, what you see on your electricity bill (at around 10p per kWh). You can then easily multiply up by the number of people in your house and days in the month to get your monthly energy consumption and energy bills.

But what about the global context? The Global Footprint Network uses a technique known as Ecological Footprinting to measure the amount of land the average person in any given country needs to support their lifestyle. This per-capita eco-footprint is measured in global hectares (gha) per person and takes into account the area of land (or sea) needed for buildings, transport infrastructure, growing crops, extracting materials and producing energy, as well as the land required to absorb waste. The methodology is well established (see this peer-reviewed journal article, for example) and there are safeguards in place to increase accuracy and avoid 'double counting' - which might occur if an area of farmland has multiple uses, for example.

We can work out whether we are using more than our fair share of land by comparing our eco-footprint against our per-capita biocapacity – the total area of biologically productive land on the planet, divided equally between everyone. The biocapacity calculation takes into account that some land types are less productive than others, so that scrubland and deserts contribute very little compared to forests and cropland. It turns out that around 1.7 hectares (2.4 football pitches) of biologically productive land is currently available to each of us.

Visit the Global Footprint Network website to explore some great infographics on eco-footprinting and biocapacity

Visit the Global Footprint Network website to explore some great infographics on eco-footprinting and biocapacity

Dividing our per-capita eco-footprint by our per-capita biocapacity we find that, if everyone in the world were to enjoy the same lifestyle that we do in the UK, we would need 2½ planet Earths. In the US, that figure is closer to 4. China, which accounts for around 20% of both global population and global eco-footprint, has more than doubled its eco-footprint in the last 20 years and is currently at around 2 planet Earths.

Exceeding more than one planet Earth means that lifestyles in these countries are unsustainable on a global scale. You might expect that developing countries with less industrialised economies might balance the books (countries like Gabon and Guyana have the largest biocapacity surplusses). However, adding up all of our eco-footprints, it turns out that we are currently exceeding global biocapacity by more than 50%. In other words, mankind is currently demanding 1½ planet Earths. In fact, historical data shows that we bypassed the natural carrying capacity of the planet in 1970. Despite the fact that global biocapacity has increased at an average rate of 0.5% per year since then - due to more efficient production of crops and land use change - increasingly resource-intensive lifestyles worldwide have meant that our global eco-footprint has increased at four times that rate.

How is this possible? Exceeding the carrying capacity of the Earth doesn't mean coming up against a brick wall that somehow caps our consumption. As the Club of Rome have pointed out in a number of versions of their famous book The Limits To Growth, the Earth system is an incredibly complex and intricate web of interacting processes and feedbacks. In any such system there is a delay between cause and effect. What this means is that for the past 45 years, we have been extracting resources from cropland and fisheries at a greater rate than they can naturally regenerate (we may have already passed 'peak soil'), and have been pumping pollutants into the atmosphere and oceans quicker than they can be neutralised by natural processes (absorption of carbon-dioxide by forests, for example). There are no big red lights flashing, but we are gradually wearing down the Earth system and the longer we continue with business as usual, the harder it will be to recover at a later stage and the more extreme the consequences could be.

Of course, we already know this and, if the recent Paris climate summit is anything to go by, it seems that many of our world leaders do too (although the way the UK Government has gone about meeting its targets is – shall we say – a little counter-intuitive). We do have options, and the compromises we need to make may not all be as severe as you might first think:

A recent BBC documentary, for example, found that eating meat is not in itself inherently unsustainable, but it is rather the current scale of consumption. If we ate half as much, we could provide meat for everybody via low intensity, sustainable and humane free range farming. Similarly, the widespread roll out of renewables is continuing, with the cost of green technologies such as wind and solar reliably falling year on year. And if the impending Malthusian catastrophe is still getting you down, try watching charismatic Swedish statistician Hans Rosling talk about how we are naturally learning to self-regulate our population.

So, as you might be able to tell, I never intended this post to be alarmist, but rather an overview of an interesting way to measure our strain on the planet. I prefer to use this knowledge as motivation for working on sustainability projects – both local and international - for my current involvement in the energy efficiency project in China and for lifestyle choices such as eating less meat. Yes, we are faced with a huge set of problems on the global stage, but we can still do something about it. The best thing we can do in the first instance is spread awareness. So please do share your thoughts and share this post.

Read more about eco-footprinting and play with some great infographics at the Global Footprint Network website.