How much are we using?

Lets start with the basic process that drives life on Earth – photosynthesis. Just how much of this process humans are making use of is controversial. As long ago as 1993, one estimate put the proportion of land plant production being used by humans at 40 percent. The jargon term here is NPP – Net Primary Production. The percentage ot NPP which humans are using must have grown since then, as jungles have been cleared for farming in Brazil, Africa and elsewhere. But despite the rise in world fish catches, the share of marine biological productivity that people are using is far lower. More recent calculations by the University of Michigan suggest that humans are using (or have killed by urbanization and other development) between 31 and 39 percent of the biological productivity of the land area of the Earth. But as we are only using about 2 percent of the productivity of the oceans, we are “only” using about 25 percent of the planets total biological production. As environmentalists point out, this is a lot for one species out of around 30 million that exist on the Earth.

Give me land, lots of land

Another way of looking at our exploitation of the Earths resources is to think about the amount of the Earths land surface that we are making use of.

Humans have been altering the landscape to suit their needs throughout history, and it is sloppy thinking to believe that only modern Western technology can have a big effect on the terrestrial environment. In most of Britain, for example, political stability, population growth and rising wealth led to large areas of the landscape being captured for food production in the seventeenth and eighteenth centuries. Now only very limited parts of the highlands of Scotland are genuinely wild, in the sense that they have not been restructured by human use. Areas such as the English Lake District are precious and beautiful, but it it were not tor people and their sheep, they would look very different. Look at the walls you see running along 1000m or more above sea level in the Lake District or North Wales. They are there because sheep have been put on the hills in numbers, removing some plant species and encouraging others. In Scotland, sheep were the main reason for the removal of large areas of forest and much of the human population during the ruthless Highland Clearances of the nineteenth century. Much of the rest of Europe – aside from such areas as the peaks of the Alps and the glaciers of Norway – has been similarly altered by human hand. And even less technological societies can alter the land fundamentally, as Australia's Aborigines did by widespread burning of vegetation.

Jim Williams of the University of California in Berkeley points out that the Earths land area is about 150 million square kilometres. Of these, about 50 million are not good for much – Antarctica, the Sahara and the like. Another 50 million is forest and another 50 million is other potentially productive land. Of the forests, 5 million square kilometres are “managed” for human use. Of the other 50 million square kilometres of usable land, 25 million are in use for agriculture, of which 15 million are used for crops and 10 million for grazing. Although it might not feel that way, the area taken up by cities, dams, mines and the like is comparatively small, under 2.5 million square kilometres. Put together into a perfect square, it would make a world city about 1600km on a side.

Williams estimates that about 15 million square kilometres of natural woodland and grassland have been converted to human use, mainly since 1700, while a similar amount has been turned to desert, a process that continues today at a rate of about 60,000 square kilometres a year. Forest destruction is continuing at a rate of 150,000 square kilometres a year in the Amazon basin alone, with more elsewhere.

Does this matter? If land that used to be an unmanaged forest turns into a sugar plantation, is the Earth any worse off? James Lovelock of Gaia fame points out that most of the areas of previously wild land now being converted to human use are near the Equator. As he says, areas nearer the poles have far fewer species of plants and animals, because every time an ice age comes along, they are bulldozed by glaciers. The warmer parts of the world escape this depletion and have the task ol repopulating the polar regions as the ice retreats. Even Homo sapiens joined in after the most recent ice age by repopulating Europe.

Running out fast: forest being cleared and made into fields in Mato Grosso, Brazil, between 2001 and 2006

This means that converting equatorial land to agriculture has a high cost in species wiped out. It also damages some of the systems that do most to keep the Earth stable. As we have seen, plants are based on photosynthesis. The tropics are as green as they are because they have plenty of sunlight and water to drive the process. So they provide very lush and diverse environments. But many failed agricultural projects in these areas suggest that it is not safe to assume that cultivation can take over this land successfully. Often severe soil erosion and other unexpected effects result in ecological damage and economic failure.

How much are we eating?

The University of Michigan scientists reckon that we are eating about 800 million tonnes of plants a year and feeding a further 2.2 billion tonnes to the animals we eat. This means that if you believe that the world is going to run out of food, a mass switch to vegetarianism is the easiest way to avert the problem. But bear in mind that a lot of the land used to graze animals, especially sheep, is not much use for crops. Only about 10 percent of the Earths surface is arable – usable for ploughing, from the Latin word for plough, ara – although irrigation, the development of new crop species and other forms of technological advance can push this percentage upwards. We are getting through 2.2 billion tonnes of wood a year, for firewood and building, and 2 billion tonnes of fish.

This means that people are using 7.2 billion tonnes a year of biological products from the land and oceans. This is just over a tonne per person, which sounds like a lot, but is only 3.2 percent of the 225 billion tonnes of plant matter a year that the Earth produces. However, agriculture is not 100 percent efficient. Add to these totals the losses inherent in growing all those crops and trees, and it turns out that we are getting through over 40 billion tonnes of biological production a year. This figure is bound to rise drastically if the billions of people in India and China start to consume something like the amount of food, wood and other biological products that people in Europe, Japan and North America take for granted.

In 2002, we ate our way through 242 million tonnes of meat. To put this in perspective, if the 6.5 billion people on the Earth weigh perhaps 60kg each on average (remember that many of them are children) that means that there are 390 million tonnes of human being. Eating as much meat as we can is one of the first things that happen as people get richer. According to the admirable Worldwatch Institute in Washington DC, meat consumption doubled between 1977 and 2002. As countries such as China and India get richer, this figure is bound to rise much further. Indeed, Chinese people are already developing an increasing appetite for beef. All those cattle need good grazing land, which has to be well watered, but because beef can command a high price, this use of land is bound to outbid products of traditional, less resource-intensive, agriculture.

Drinks all round!

In 2000, 2800 cubic kilometres of water were used for agriculture, 800 for industry and about 600 for domestic use. This last figure might miss some water gathered and used locally in the developing world, but the total under this heading cannot be very great. The total, 4200 cubic kilometres, might sound like a lot, but it is only a tiny percentage of the fresh water on the planet.

So why the constant news stories about water shortages? The problem: geography. With a world-traded resource such as oil or coal, it might be worth thinking how much of the available material we are using per year. But there are no sharp-suited water traders making fortunes by speculation in London or Chicago. We have to think about the issue in regional rather than global terms. Thus by one count, Canada has 20 percent of the Earths fresh water and 0.5 percent of the people. China has 7 percent of the water and 21 percent of the people. Unless most of them move to Canada there will be growing stress on rivers and groundwater in China. The same goes for Europe, large parts of North America, and growing areas of Asia.

In some areas, old groundwater reserves are being mined far faster than they can be replaced. Populous, dry areas such as the Middle East are especially prone to this unsustainable behaviour. Some of the
aquifers that are being depleted formed in the past when the climate was wetter in these areas, and are essentially fossils. But the special paper on groundwater produced for the planned International Year of Planet Earth (set to be in 2008) points out that some of these reservoirs are very large. One, the Nubian Sandstone Aquifer, underlies parts of Chad, Egypt, Libya and Sudan and contains about a century of humanity's current water use.

Many observers have pointed out that water shortages in the developing world have severe effects on health and economic growth. Solving these problems will mean more water abstraction. But there is also scope for improved practices. By comparison with most economic activity, water use is exceptionally inefficient in most countries. Economists say that this happens because water is regarded as cheap or free in many parts of the world. Whatever the reason, the UN says that about 60 percent of irrigation water gets lost before it sees a field, and that in some cities, a third of the water gathered escapes before it gets to the tap. Political encouragement for cleverer water use might postpone severe water problems. More to the point for the Earth itself, it could allow more lakes and rivers to be left in a comparatively natural state rather than being dammed or encased in concrete.

Fossil fuels and minerals

The damagingly low cost of water is stressed by the International Year of Planet Earth documents. They point out that each year people use over 600 billion tonnes of groundwater alone, leaving aside river and rain water, at a cost of perhaps Ђ300 billion. By contrast, coal and oil production total about 8 billion tonnes – priced at Ђ926 billion.

Oil is the biggest internationally traded commodity, ahead of coffee in second place. In 2006, President George W. Bush claimed that the US is “addicted” to oil, and it is certainly true that all rich societies depend upon it. How severe is their addiction?

In 2005, oil giant BP estimated that the world had about 1190 billion barrels of oil in the ground. That is about 160 billion tonnes. Of that, about 80 million barrels a year are being extracted. While more oil is
being found every year, consumption is growing faster, so that the ratio of reserves to production had fallen to just over forty years in 2004.

The picture changes (again using BP's numbers) if you look at coal or gas. There are about 180 trillion cubic metres of gas available, equal to 68 years of consumption, although gas use has been growing apace. For coal, there are 909 billion tonnes, but we are “only” getting through about 5.5 billion tonnes a year of all types of coal, so we have almost 200 years' worth in the bank.

Move away from fossil fuels into other minerals and the picture is less urgent. Although I have never heard of any nation invading a foreign country to get access to its gravel, the figures show that world use of sand and gravel totals about 18 billion tonnes a year. Much of the gravel that is used was made by glaciers scraping Europe, Russian Asia and North America during the last ice age and we will have to wait for the next one for it to be replaced. Sand, by contrast, is made every day by the erosion of rock. Because they are the staples of the building trade, their use dwarfs that of all other minerals. The remainder add up to about a billion tonnes a year, of which iron ore accounts for about two-thirds.

The difference between using iron ore and using oil is that iron can be recycled, as the big world trade in scrap shows, while a hydrocarbon that is burnt cannot be burnt again. With solid minerals, the real issue is the environmental damage caused by extracting them from the Earth and transporting them around the world – a problem predicted to grow as billions of people in China and India start to demand similar levels of consumption to those seen in the developed world.