In my last column, I wrote about pollution, and about how very small quantities of man-made substances can disrupt the biology of some animals.

I described some of the examples that we know about.

But what about all the consequences that we don’t know about?

New substances may be tested for their effect on human health, and perhaps some other things as well, but they can’t possibly be tested for their effects on every living species.

When we release something into the environment, we just don’t know how it will affect all the living things with which it comes into contact.

Margaret Thatcher, in a speech to the Royal Society in 1988, said that "we have unwittingly begun a massive experiment with the system of this planet itself."

The thing about an experiment is that you don’t know the outcome.

We don’t know the damage that will be done by all the different ways in which our lifestyles interfere with the natural processes of the earth.

When Rudolf Diesel developed the engine that is named after him, when Paul Müller discovered the insecticidal properties of DDT, when Thomas Midgley developed a process to manufacture CFCs for use in refrigerators, they had no idea of the effects of these products on human health and the environment.

Bees and numerous other species are in decline.

Can this be attributed to changing land use leading to habitat loss?

Or chemicals released into the environment?

Or climate change?

Or natural causes?

Or to the interaction of two or more of these factors?

We are learning more and more about natural processes and how human activities can disrupt them, but it remains true that we, as humans, are conducting a massive experiment with this precious and fragile planet of ours, with very little idea of what the consequences might be.

Henry Haslam is the author of The Earth and Us.