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|Prophets of Doom: Where will Global Warming take us?|
Man's eviction notice from Mother Earth
The English demographer and political economist Thomas Robert Malthus, (1766 to 1834), once postulated that as population growth was exponential and growth in food production essentially linear, there would come a point where the population would crash due to famine. Since the days of Malthus, technology has dramatically increased yeilds from land. So in spite of something like a sevenfold increase in global population food is if anything, more plentiful. But just because it hasn't happened two centuries later does not mean Malthus was wrong. The world population is growing while land is clearly not and yeilds cannot keep rising forever. Ultimately unless the world population stabilizes, Malthus will be proved right. As to when this might be is anyone's guess. If one only looks at yield potential and population growth figures a Malthusian famine lies at least another two centuries into the future. Especially if one accepts that economic growth will slow population growth as it seems to be doing.
But farming yeilds and population growth are not the only factors in the equation. Our increasingly hazy sky, ever more bizare weather and ever smaller ice caps show the downside of our history of ecomonic growth. The changes in the atmosphere threaten to reduce available land by rising sea levels and threaten yeilds with alternating extreams of drought and flood. And the changes are accelerating. Malthus could be with us not in another two centuries, but within the lifetime of children alive today. Global warming is an eviction notice to man from Mother Earth. Either we change our ways or very large numbers of us will be hastened to our final destination. If we fail to comply with this notice the baliffs won't be the usual gormless goons, they are going to be the four horsemen of the apocalyse.
The runaway greenhouse
As well as absorb energy, all objects radiate energy and the intensity and type of radiation depends on their temperature. Objects on Earth are warmed by sunlight and emit infrared radiation which largely escapes into space. This limits the extent the Sun can warm us up. A greenhouse maintains a higher temperature than the outside because the glass allows through the sunlight but reflects the infrared emitted by the plants back into the greenhouse. Certain gasses such as carbon dioxide have a similar effect to the glass, hence the term 'greenhouse gases'. Technically such gases do not reflect infrared, they absorb it and warm up as a result. But the overall effect is the same. The more carbon dioxide there is in the atmosphere the less infrared escapes into space and the warmer the Earth will be.
Sitting in a greenhouse during a hot day is not recomemded. You could even die of heatstroke if you are in there too long. Clearly the greenhouse gas thing is not as effective as a real greenhouse. This is because there isn't much carbon dioxide in the atmosphere yet (about 380 parts per million) and because carbon dioxide is not a particularly powerful greenhouse gas. No problem then surely? After all we could do with the weather being a little bit warmer! An understandable sentiment but alas rather shortsighted. Mother nature's eviction notice comes with a few more teeth. The global warming we are seeing so far is melting the ice caps. Slowly yes, but at a rapidly increasing rate. Not only will melting ice caps result in rising sea levels and the dissappearance of low lying land, but burried in that ice is a truly vast quantity of methane - another much more powerful greenhouse gas. And as the methane escapes into the atmosphere, the Earth's average temperature will rise more rapidly which will melt the ice caps much faster drowning yet more land and releasing yet more methane. As the planet warms up so humidity levels will rise and guess what? Water vapor is an even better greenhouse gas than methane! We all know clouds are made of water vapor and it is a matter of common experience that a cloudless winter night is a lot colder than a cloudy one.
Some people have suggested this runaway greenhouse effect could boil the oceans and make the Earth like Venus. It is about 450°C there, far hotter than Mercury which is much closer to the Sun - A true testament to the potential of greenhouse gases. We won't get to be as hot as Venus because we are further out but that is of little consellation. If temperature rise another 30 degrees we are as good as extinct and this sort of rise cannot be ruled out. There are counter arguments. The rise in water vapor will to some extent be self limiting as clouds reflect sunlight back into space. But it is worth noting that one of the most reflective atmospheres we have yet discovered, is that of Venus.
Nobody knows how far global warming will go but it is likely we will be faced with a permanantly grey sky with high temperatures and very high humidity. We would go mad if nothing else. Plants can't do much under such conditions either as they need direct sunlight to grow efficiently. They also need rain and under this scenario there will be precious little of that. We have the rainfall levels we have because direct sunlight reaches the water's surface. Without the direct sunlight evaporation would virtually cease and without a moderate temperature precipitation would virtually cease. And with plant's struggling a Malthusian famine is inevitable.
The threat from the sea
And it is not just the atmosphere that is warming up, the temperature of the sea is rising as well. The rise in sea temperature will directly kill fish but the lack of sunlight will also kill plankton near the surface. This will shut off most of the oceanic food chain leaving only the hydrothermal vents and the tubeworms that surround them. A mass extintion at sea when we are going mad and having a famine with our failing plants might not make headline news but it will only be a matter of time before it does. A few billion dead fish won't matter if the dead fish are eaten by other fish still alive. But in a mass extinction scenario there will be no living to eat the dead and the dead will rot. One of the products of this wholesale rotting will be a gas called hydrogen sulphide. It is the one responsible for the 'bad egg' smell. But we won't have to put up with bad eggs as well as grey skies because in sufficient concentration we cannot smell it. Unfortunately at the level where we can no longer smell it, hydrogen sulphide is a dangerous poison. It is in fact, more poisonous than cyanide.
Could it really get that bad?
The simple truth is nobody knows. The Earth is a very complex system. We do not know all the feedback loops let alone understand them. We know carbon dioxide dissolves in the sea but we don't what at what rate or what the fish do with it. We know levels of carbon dioxide have varied over time by natural processes that took place long before we embarked on our orgy of carbon fuel use. But we don't have a clue what caused these variations. We all have a common sense that tends to filter out farfetched scenarios such as the one described above. But sometimes our common sense fails us and the 'unthinkable' beomes reality.
One thing that is certainly true is that we are taking a risk by continuing to burn carbon based fuels. And it is a risk that we cannot calculate and that definitely could be catastrophic. Nobody can yet prove we are safe and if we cannot prove we are save we cannot dismiss or ridicule the worse case scenarios. So if we cannot afford to laugh at a prophet of doom, maybe the smart thing to do is to listen to him.