Resources and renewal

What makes a resource renewable?

A resource is something people can use, such as water or plant material. Replenishment means replacing a supply after some has been used. To judge renewal, ask what replaces it and how long that takes

1. 1Renewable A process can replace the supply on a human timescale, such as seasons or years
2. 2Non-renewable The used supply is not replaced on a human timescale. Formation over millions of years is too slow for this

Look for replacement, not just usefulness

Suppose plant fibres grow back over the next growing seasons. Growth replaces the harvested material. That supports calling the fibre renewable under these conditions

1. 1A different timescale A deposit that forms over millions of years is not replaced within human lifetimes. It is non-renewable on that timescale
2. 2Neither label means good or bad Both resources can be useful and naturally occurring. Those facts alone do not tell us whether a used supply is replaced

A resource is something people can use. A field produces new plant fibres each growing season after harvest. Which fact tells us about replacement of this resource?

Replacement can be smaller than use

Stock means the amount available. Collected water adds to a store; used water leaves it. Compare both amounts over the same week and in the same unit. L means litres

1. 1More collected If collection is greater than use, the stock rises
2. 2Equal amounts If collection and use are equal, the stock stays the same
3. 3More used If use is greater than collection, the stock falls, even though some water has been replaced

Before moving the controls, predict what happens when use is greater than collection during one week

A water store begins a week with 60 L. Rain adds water and people use water. Assume no leaks, overflow or other changes. Keep collected water at 10 L and move used water below, equal to and above 10 L. Then hold use fixed and change collection. The model shows one week, not a forecast

Can the amount stored fall even while some water is collected?

How far does the evidence take us?

One week of data tells us about that week, not every future season. A dry week does not prove that a water store can never refill. More evidence about the replacement process and a suitable period is needed

1. 1Finding is not replacing Discovering more existing material does not create a replacement supply. Its formation timescale has not changed
2. 2Keep impacts separate Even if replacement matches use, that alone does not show the effects on habitats, soil, water or people
3. 3Model limits The water-store model compares amounts for one week. It cannot tell us all future rainfall or all environmental effects

A deposit forms through geological processes over millions of years. Material removed from it is not replaced on a human timescale. Which classification fits this evidence?

A class records no rain entering a water store during a dry week. It has no longer record. Which claim can it make?

A plant fibre can regrow. Over a season, a site grows 7 kg of new fibre and people harvest 11 kg. Assume no other gains or losses. Which statement is supported?

Three questions to take away

What replaces the supply, and how long does that take? Does replacement keep up with use over the same period? How much can the available evidence tell us?

1. 1Keep the distinctions Renewable does not mean unlimited or impact-free. Discovery is not renewal. One short record is not a long-term forecast