The tropical rain forests and the oceans are two of the planet’s, and humanity’s, greatest assets.

Yet we are grossly mismanaging this global portfolio and will pay a very high price unless we develop mechanisms to turn it round.

The forests are the lungs of the world, but they are being felled at an alarming rate to make money from timber, mining, plantations and ranches.

We fill the seas with pollutants, overfishing and doing yet more damage with seabed mining.

Not the smartest way to treat an asset that is an immense source of food and one of our most important carbon sinks.

At the Wigtown Book Festival this Saturday I’ll be delivering the second annual James Mirrlees Lecture.

It was founded to commemorate the Nobel Prize-winning Galloway economist, and a man who was enormously important in my life as a mentor when I was a PhD student at Cambridge, and a professional colleague for many years afterwards.

An idea I will be arguing for is a collaboration by world governments to tax the use of the oceans - for example by mining operations, container ships and cruise liners -and use the billions of dollars this would raise to halt deforestation.

As I suggest in The Economics of Biodiversity: The Dasgupta Review, this would help tackle some immense economic problems. For example, conventional economic thinking – used by governments, businesses and international agencies – does not account for the depreciation of capital assets that takes place due to production.

Nature is the greatest capital asset of them all.

That means things can look good for some time, cheap products and high profits, but all the time we are hollowing out the assets we depend on.

No one paying for the damage done to the seas or rain forests or the use that’s made of them.

There is no built-in recognition of how immensely productive they are; giving us clean air, biodiversity, a liveable climate – keeping us alive.

Unless these are costed in they will not be valued, the damage and destruction will continue and there will be no proper reinvestment to ensure a sustainable world.

Ranches and plantations are far less productive than rainforests.

But for countries trying to develop their economies there is currently too little incentive to stop deforestation - they have an immediate gain from the artificially cheap beef that we are only too willing to buy.

That only stops when our economic system ensures we pay a full and fair price for what we do and all we consume.

In the West we are already accustomed to paying farmers for ecosystem services like nurturing biodiversity rather than using land for crops or livestock.

We need to extend these principles, recognising that countries which sustain rain forests are performing vital ecosystem services - paying them enough to mean that deforestation becomes a financial nonsense.

Nothing is free, and unless we pay a proper price now and use the proceeds to sustain our ecosystems, it will cost us the Earth.

Prof Sir Partha Dasgupta is a world-renowned economist