The resources  provided by the Earth and its environments underpin our economy; without these resources our economic activity can't happen. The ability of the Earth to provide these resources for us to use in our economies is limited.

The way that we use renewable resources is analogous to the way that we use an investment account's principal and interest. An investment account contains a quantity of money (the principal) that the account provider pays interest on. The principal is equivalent to the stock of a renewable resource, and the interest is analogous to the growth of that resource stock.

You can use an investment account in one of three ways: you can spend the money in it to buy what you want now, and close the account; you can decide how long you want the investment account to last, and calculate how fast you can spend the money (and the interest it collects) to make it last that long; or, you can spend only the interest that it collects and have it last forever.

The outcome that you choose is realised by the rate at which you withdraw the money from the account as you spend it. If you withdraw is slowly enough, it will last forever; if you withdraw it quickly enough, it will be gone almost straight away. That's how it is with our renewable resources; if we use them at a sustainable rate so that we aren't using up the principal, then we can use them forever.

Finite resources don't work like this, because they have no growth that is analogous to the interest of an investment account. Finite resources work like a cheque account: there is no interest, and once you use it, it's gone!

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limits to the use of resources

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