THERE have been numerous letters recently, commenting on Climate change, some agreeing it is happening, and one or two, with no scientific basis, adopting a "head in sand" stance of denial.

Without doubt, it is happening and the only area left for debate is what the consequences will be.

The problem here is there are so many factors that have to be considered when predicting possible outcomes that a mathematical model can only deliver a wide range of possibilities, with no precise answer.

Take just one aspect. The effect of melting ice on sea levels is of crucial importance, since many millions of people live within one metre of the current mean level. Near to home, for instance, a huge proportion of Holland is within, or below, this point.

So what effect will melting ice have on the mean sea level? This is where things get incredibly complicated! Floating ice, if it all melted, would make only a small difference, because as many will remember from school physics, ice in a glass of water makes no difference to the water level as it melts.

But sea ice is different. The oceans contains dissolved salts, and are thus more dense, so melting ice will marginally increase sea levels.

Ice on land, when melting, will of course eventually raise levels as it drains to the sea.

So far, it seems simple, but then other factors enter the equation. Removing large areas of sea ice removes a huge area of white surface cover which currently reflects sunlight, and instead, the sea will be directly exposed and warmed by the sun.

However the melting ice will cool the surrounding sea; why else do we put ice in our drinks? So what will the net change of sea temperature be?

Then we must consider the effects on the major ocean currents, which are the drivers of local climates. The oceans are subject to a layering effect with temperature differing at different levels, but an influx of colder water may well influence this and possibly cause inversion or even significant change of direction of the currents.

We would suffer badly in Britain if the gulf stream were to change or cease to warm our shores.

Yet another consideration is the rate of evaporation from the sea. As temperature rises, evaporation will increase, with consequent higher cloud cover and rainfall, but where this will fall is also tied in to wind patterns and ocean currents.

So all these and other factors have to be put into a gigantic set of mathematical equations, with dozens of variables, and "if..then" outcomes. So it is easy to see why there can be no precise figure put on what will happen to sea levels.

However, it is known that the mean level has risen between 10 and 20cm in the last 100 years, more than in the previous 2,000 years.

The best predictions that science has been able to derive from this incredibly complex issue is the sea is likely to rise between 10 and 89cm by the end of this century, and with the likeliest outcome being below the maximum figure, unless we miraculously find ways of slowing or halting the temperature rise.

Of course the alarmists will always seize on the worst predicted outcomes, and the denial lobby, the lower figures to argue their case.

But the reality is, that as so often, we do not know just how bad things will be, so should hope for the best, while preparing for the worst.

Mike McVeigh