How much of the land on Earth is covered by humans? (Asked by Lynne)
This question is an interesting one because, when my friend asked me the other day, I could tell her confidently that not only did science know the answer, science had multiple different ways to quantify that answer, but that I had absolutely no idea what it was.
Landcover is one key way that we can measure how much of the terrestrial environment has been covered by humans. Earth’s surface is about 500 million km2, but most of that (70.8%) is water, which we’re not really very good at. So ignoring oil rigs and the occasional cruise liner, we’re only talking about a total possible land surface to cover of roughly 149 million km2.
The thing is, landcover is something that is changing (and our technology to estimate it is improving) constantly, so even fairly recent estimates may already be out of date. A meta-analysis in 2011, which included 326 studies of urban landcover using remote sensing technology such as satellite images, found that urban landcover increased by nearly 60,000 km2 between 1970 and 2000.
In the year 2000, estimates suggest that globally, urban land covered somewhere between 700,000 and 3.5 million km2 – but that’s a pretty big margin of error. The meta-analysis found that the largest rates of increase in urban landcover were seen in India, China and Africa, while North America experienced the largest total change since 1970. In all regions, urban land expanded either faster or equivalent to population growth rates, suggesting our societies are also becoming more expansive.
Using data from 1970 to 2000, the researchers then tried to project future urban land cover change – their results predict that global urban landcover will increase by a further 1.5 million km2 by 2030. Over half-way to this prediction, where are we now?
According to the FAO Global Land Cover SHARE database, produced in 2014, 0.6% of Earth’s land surface is defined as ‘Artificial surfaces‘. Artificial surfaces include any areas that have an artificial cover as a result of human activities such as construction (cities, towns, transportation), extraction (open mines and quarries) or waste disposal. This figure gives us an estimate of roughly 900,000 km2 of human-covered land worldwide. This suggests the lower end of the estimates made in 2000 were probably more accurate, and that we’ve still got a long way to go before we hit Seto and colleague’s projections!
However, even non-urban areas contain roads, train tracks, farms and other marks of human domination. The FAO GLC SHARE data shows that 12.6% of land is categorised as cropland. If we include this to our estimate of global human cover – we get a rather more sobering estimate of 19 million km2. In 2009, the European Commission’s Joint Research Center published a map in the World Bank’s World Development report, showing that 95% of the world’s population is concentrated in just 10% of the land surface. However, only 10% of land on Earth was considered ‘remote’ – more than 48 hours from a large city.
So on the one hand, you could say from these results that 10% of Earth is inhabited by humans. Or you could take a more glass half-empty view and say that 90% of Earth is covered by humans – either populated or connected with an ever-expanding network of roads, train tracks, highways, farms and industrial land. Only 10% of the world is truly wilderness.
Want to know more?
- Seto, Fragkias, Güneralp, and Reilly (2011) A Meta-Analysis of Global Urban Land Expansion PLOS ONE
- Parashar (2012) Philosophy of Everyday Life: What percentage of the world’s land is populated by humans? Quora
- Current global land cover maps
Featured image from MODIS is in the Public Domain.