The process of making paper starts with the raw wood, which tends to come from softwood trees like spruce, pine and fir, as well as some fast-growing hardwoods like eucalyptus. Whichever type it comes from, wood is made up of cellulose fibres bound together with a natural glue called lignin. So the first step involves removing most of the lignin, to allow the cellulose fibres to separate and be re-moulded into a different shape.

But it turns out that breaking down a material that’s strong enough to support giant plants is no easy feat. “The chemistry is quite complicated, but the main goal is to remove the lignin to the maximum extent possible,” says Siddharth Chatterjee, an expert in paper engineering from the SUNY College of Environmental Science and Forestry, New York.

First there’s the “pulping” process, which usually involves breaking the wood down into chips, and then cooking it in a bath of sodium hydroxide and sodium sulphide. These are potent alkalis, capable of inflicting serious burns, and dissolving aluminium and rock, as well as – crucially – the lignin in wood. Another option is to leave the lignin in and just physically mash the wood instead, but this produces a low-quality paper that is only really suitable for newspapers and phone books.

At this stage, the paper sludge is still very much brown, because that’s the colour of lignin and it’s not possible to remove it all in one go. So now chlorine dioxide is added, to bleach the pulp and achieve a white colour. Finally, a thin layer of pulp is sprayed onto moving mesh screens, before it is dried and pressed, expelling water.

Indeed, almost every phase of paper manufacturing involves water. Scaled up to the magnitude of the industry today, a vast amount is required. To make just a single A4 sheet, you need between two and 13 litres. In China, which remains one of the leading players in the paper trade, the industry sucked up 3.35 billion tonnes (roughly three trillion litres) in 2014 – enough for about 37 billion baths.

After the pulping and bleaching is over, paper mills end up with water containing a cocktail of organic compounds, alkalis and bleach, which must be treated so that it can be disposed of safely. This can be a huge technical challenge, and some paper mills simply discharge the effluent straight into the local water supply, where it’s acutely toxic to fish and other wildlife – even at concentrations of just 2%.

Another sustainability challenge facing the paper industry is the sheer amount of energy required. One study found that the global paper industry eats up around 6.4 exajoules (EJ) of energy each year – enough to make some 87 trillion cups of tea. All that energy means paper contributes 2% of the world’s total carbon footprint.

And finally, there’s the trees. Each year, the global paper industry is fed by more than 100 million hectares of forests, which is an area around the same size as Egypt. In some places, the industry is thought to contribute to net deforestation – and therefore yet more carbon emissions, because the felled areas would previously have been locking away carbon dioxide. And while much paper is sourced from sustainably managed forests, some is made from trees in ecologically important forests, contributing to loss of biodiversity.