The lowest point of land in Britain is a cast-iron post in a Cambridgeshire wood, and when it went in the ground it was level with the ground. Stand next to it now and it is four metres over your head. It is at Holme Fen, south of Peterborough, and in 1851 this was the edge of Whittlesey Mere, the largest lake in southern England. A syndicate of landowners drained the lake that year for farmland, and the engineer, who knew what happens to peat when you take the water out of it, drove an oak pile through 22 feet of it down to the clay and cut the top flush with the turf. A column from the Crystal Palace replaced it. Then they stood back and watched the land go down. Nine inches in the first year. Eight feet by the 1890s. Today the ground around that post is 2.75 metres below sea level, and the post is a ruler nobody asked for, sticking out of a birch wood with guy ropes holding it up because the soil that used to hold it up has gone into the sky. That is what drained peat does. It dries, it shrinks, and it oxidises, which means it turns into carbon dioxide and leaves. Peat takes a thousand years to lay down a metre. Under the plough it loses a centimetre or two of that every year, and the Fens have been under the plough since the Dutch engineers arrived in the 1600s. Peat soils farmed for crops are among the largest sources of carbon dioxide in Britain's whole land sector, and the fields doing it are growing lettuce. Because that is what the Fens are for. A third of England's vegetables come out of this one flat black square: half the lettuce grown in Britain, three quarters of the celery, the carrots, the onions, the potatoes, the leeks, the beetroot. The bag of salad, the celery sticks, the chips. Every field of it is a few millimetres lower than it was last January, the pumps run day and night to keep the sea out of a landscape that is now beneath it, and the water the crops need is forecast to run short within ten years. Before the drain this was eels, wildfowl, reeds, summer grazing, and a fen that had been quietly stacking carbon since the ice left. The cattle came and went on it for 5,000 years and the ground stayed where it was. The salad has been on it for 170 years and the ground is four metres down. The post is still measuring.

On a beach in West Africa the fishermen now haul in more clothes than fish, and the clothes have your charity shop's label on them. The beach is in Accra, the capital of Ghana. A mile inland is Kantamanto, the biggest second-hand clothes market on earth. Every week about 15 million garments arrive there in bales, from Britain, Canada, China and America. Most of what you drop in a clothing bank ends up on its way to a place like this. The locals have a name for the trade. Obroni Wawu. It means dead white man's clothes, because nobody could imagine a living person giving away so much. The traders open the bales and sort them. 40 years ago nearly everything sold. Now about 40% of every bale is rubbish before it leaves the market, because the garments were built to be worn 5 times. That is 6 million pieces of clothing a week with nowhere to go. The city collects what it can. The rest goes into the gutters, the lagoon and the sea. Then it comes back. The waves roll the clothes together into ropes of knotted polyester as long as a boat, and the beach monitors who count them have a word for those too. Tentacles. They logged 2,344 of them along 4 miles of shore in one year. Fishermen's nets come up full of trousers. Propellers foul on them. Men have had their canoes capsized by somebody's old leggings. A fishing community cannot fish, because of what the rest of the world was too virtuous to throw in its own bin. When those clothes were wool and cotton they would have rotted on that beach in a season. Instead they are becoming the coastline.