Resources and environment

Non-renewable

HintIt is a metal ore dug from the ground, and there is only a fixed amount of it.

The whyCoal, oil, gas, metal ores and uranium all form far slower than we use them. Wind, sunlight and flowing water replace themselves constantly, and timber does too - but only while it is replanted as fast as it is cut.

Abiotic

HintThe prefix means 'not' - these are the parts of a habitat that were never alive.

The whyLiving things depend on non-living conditions: rainfall, temperature, soil depth and light decide which plants grow, and the plants decide which animals can live there. Change one non-living factor and the whole food web shifts.

Freeze-thaw weathering

HintIce takes up more room than the water it came from, so it prises the crack wider.

The whyWater expands by about a tenth as it turns to ice, wedging cracks open a fraction each night until a fragment splits away. It is why British uplands are littered with scree.

Humus

HintThe dark, crumbly matter that makes good topsoil rich.

The whySoil is a mixture of weathered rock fragments, rotted remains, water, air and living organisms. The rotted part stores nutrients and holds moisture, which is why losing topsoil is so serious.

The canopy

HintA continuous green roof about thirty metres above the ground.

The whyIt intercepts most of the light and rain, leaving the forest floor dark and still. A few emergents push through above it, and the shrub layer sits below.

Poor

HintAlmost everything the forest owns is locked up in its trees, not the ground.

The whyHeavy rain washes nutrients out, and what remains is recycled straight from fallen leaves back into the roots. Clear the trees and the fertility leaves with them after a few harvests.

Cattle ranching

HintThe trees are burnt to open up grazing for herds destined to be beef.

The whyRoughly two-thirds of cleared Amazon land ends up as pasture, with soya, logging, mining and road building behind it. Because the soil is poor, ranchers move on and clear more after a few years.

About 300 000 tonnes

HintMultiply the store held by one hectare by the area cleared, then keep the units.

The whyTwo thousand lots of 150 tonnes is 300 000 tonnes of carbon, which burns to roughly 1.1 million tonnes of carbon dioxide because each carbon atom picks up two oxygens. That is why tropical deforestation accounts for about a tenth of global emissions.

plankton

HintMicroscopic drifting life in ancient seas - not trees.

The whyCoal comes from ancient swamp forests, while oil and gas come from tiny sea creatures buried in mud and cooked over hundreds of millions of years. All three are fossil fuels, and burning them releases carbon locked away that long ago.

Economic water scarcity

HintThe rain falls; the money to store and pipe it does not exist.

The whyPhysical shortage means the supply simply is not there, as across the Sahel. The other kind means it is there but unreachable, which is common in central Africa - a poverty problem rather than a rainfall problem.

Intensive farming

HintSqueezing a bigger harvest from every hectare rather than clearing more hectares.

The whyThese methods fed the population boom of the last century, but they cost energy, water and soil health, and fertiliser run-off pollutes rivers. Cutting waste is cheaper - about a third of the food grown is never eaten.

The primary sector

HintFarmers, miners and fishing crews all work at this first stage.

The whyThis work extracts raw materials, the secondary sector manufactures, the tertiary provides services and the quaternary handles research and information. As a country develops its workers shift towards the last two.