The classic Malthus argument is that populations will grow exponentially until they are nonlinearly suppressed by famine or disease due to overcrowding. However, the lesson of the twentieth century is that populations can be checked for other reasons as well. This is not necessarily a refutation of Malthus per se but rather that the quantity that populations conserve need not be restricted to food or health. There seems to be a threshold of economic prosperity when family income or personal freedom becomes the rate limiting step for a bigger family. Developed nations such as Japan and Germany are approaching zero population growth and trending towards negative growth. Russia currently has negative growth.
Hence, we can slow down population growth by increasing economic growth. China is starting to see a very steep decline in population growth in the big cities like Shanghai that is independent of the one child policy. The emerging middle class is now taking into account the cost of raising a child and how it would affect their lifestyle. In a very poor country, the cost of raising a child is not really an issue. In fact, if the probability of a child making it to adulthood is low and help from children is the only way for the elderly to survive then it is logical to have as many children as possible. In this case, the classic Malthus argument with food and health (and aid) as the rate limiting quantities applies.
I bring this point up now because it is crucial for the current debate about what to do about climate change. One way of mitigating human impact on the environment is to slow down population growth. However, the most humane and effective method of doing that is to increase economic growth, which will then lead to an increase in emissions. For example, in 2005, the US produced 23.5 tonnes of CO2 equivalents per person, (which incidentally is not the highest in the world and less than half of world leader Qatar), while China produces about 5.5 tonnes and Niger 0.1 tonnes. (This is not accounting for the extra emissions due to changes in land use.) In absolute terms, China already produces more green house gases than the US and India is not far behind. On the other hand the population growth rate of Niger is 3.6%, India is 1.5% and dropping, China is 0.6% and the US is 1%. So, when we increase economic prosperity, we can reduce population growth and presumably suffering, but we will also increase greenhouse gas emissions.
Given that the world economy and agricultural system is entirely based on fossil fuels, it is also true that, at least on the short term, a restriction of carbon emissions will slow down or reduce economic growth. Thus, even though climate change could have a catastrophic outcome for the future, curbing economic growth could also be bad. Thus, for a developing nation and even some developed nations, the choice may not be so clear cut. It is thus no wonder, that the current debate in Copenhagen is so contentious. I think that unless the developed world can demonstrate that viable economic growth and prosperity can be achieved with reduced carbon emissions, the rest of the world and many people will remain skeptical. I don’t think the leaders in the climate change community realize that this skepticism about carbon restrictions may not be all irrational.