Warming to global estimates

I hesitate to challenge Mr Fox and his ice-in-a-glass experiment but my distant memory of O level physics tells me the narrow scope of his experiment may have misled him.

Water, although a common substance, is very unusual in that it expands when it changes from liquid to solid state (most things contract).

This expansion is one reason why ice forms at the surface of a pond - it is less dense than the water.

Once ice has melted into water, it expands as it warms up, like everything else. In fact, water is at its most dense at four degrees C, and sinks to the bottom of a pond, which is good news for fish trying to survive a freeze.

From his description, it seems Mr Fox only left the ice in the glass until it had melted, when the ice had thus shrunk and the water had become colder.

Out of interest, I heated some very cold water up to 60 degrees (the limit of my thermometer) in a measuring jug and I I have to admit I could see no discernible increase in volume.

Nonetheless, David Attenborough, in his recent programme, quoted scientists' calculations of how much sea levels would rise from warming five to 10 degrees or so and, because of the huge size of the oceans, the rise was considerable.

Michael Carter, Shrewsbury