The Human Crisis.

By 2050, if the demographers have got their sums right, the world's human population will be over 9 billion. About 120 million of them will be suffering from some form of senile dementia, because we will all be living longer.

These people will need feeding, watering, housing, and clothing - at a bare minimum. Most of them will want rather more than that. They will want the lifestyle that goes with the material prosperity that advanced industrial society can give them, if they are smart enough, and work hard enough.

All of this will take energy, and lots of it. There will still be plenty of coal to burn - at least another 90 years' worth, but the oil and natural gas will have run out. There may still be some in the ground, but it will not be accessible for economic, technological and/or geopolitical reasons.

The burning of all that fossil fuel will have added an enormous amount of CO2 to the atmosphere. It is already over 387 ppmv, and is expected to reach 400 ppmv inside a decade. That level of atmospheric carbon dioxide hasn't been seen for the last 20 million years - not since the Miocene Period, when there were no Polar ice-caps, and sea-levels were 24.384 metres (80ft) higher than they are today.

In addition to the problem of climate change, will be that of loss of drinking water supplies and food shortages, for example caused by de-salination and acidification of oceans and seas destroying fish stocks, or droughts and floods destroying grazing land and crops. Over-population will itself mean an excess of demand over supply, and if the poor cannot afford higher prices, then they will starve.

The easiest way to solve all of the problems confronting us is to reduce our population. The fact is, there are too many people on this planet now. There are 6.79 billion of us, and we are generating 28.4 billion tonnes of CO2 annually (2006 figure, IEA), or 4.18 tonnes each. That is quite apart from all the other long-term greehouse gases we are putting into the atmosphere, such as methane (110 million tonnes annually, from all sources, including non-human) and nitrous oxide (22 million tonnes annually).

Earth's total land area is 148 million square kilometres - which includes the Himalayas, the Sahara, and the Antarctic, among other inhospitable places. Our current population density is ~45.88/sq.km. If the population reaches 9 billion, it will be 60.81/sq.km. In fact, it will be higher - because there will be a loss of land surface to the sea, as global warming causes sea levels to rise. Already, the densely populated country of Bangladesh - one of the poorest countries in the world - is under threat.

We have to act soon, or it will be too late. But will the politicians heed the scientists' warnings, or will they prefer to do nothing, or take half-baked half-measures, just to appease public opinion? I fear they will do the latter, and then too late, in any event. So what is to be done?