This paper seeks to ascertain the extent, if any, continued population growth will have on global warming, through the examination of works by Bongaarts, Gilland, and Mackeller. Global warming is a sustained rise in average global temperatures, and it has received much international attention due to the severe consequences that could result from the warming of our planet. However, one problem is that the situation is very complex as it involves the interaction of multiple variables, making it very difficult to clearly identify the problem and make reasonable predictions. Global warming is itself debated between those that see it as the result of an intensification of the greenhouse effect, and those that look to the history of global climate and see recent trends as an aspect of the natural variability of climate. Either way temperatures seem to be rising with the 1980s the hottest decade on record (Bongaarts, 1992).
(Source:http://www.epa.gov/globalwarming/climate/index.html)
The greenhouse effect occurs naturally from the presence of gases such as Carbon Dioxide (CO2) in the atmosphere that insulate the earth. But the concentration of these gases is increasing due to human activity. For example, the concentration of CO2 has increased by 25% from the combustion of fossil fuels (Bongaarts, 1992). There is a chain of causation:
Human Production Emission of Atmospheric Concentration Global
And Consumption = Greenhouse = of Greenhouse Gases. = Warming
Activities. Gases.
Such attention has been given to this topic because of its far-reaching consequences that there is now international agreement that it is a problem and there will be slow but significant warming if current trends persist. Estimates but the figure around a 4oC rise depending on climate sensitivity (Bongaarts, 1992). The main affects of this warming will be to change weather patterns and climates. This will generate species migration to more suitable environments, melt the ice caps to produce a sea level rise, and increase the incidence of severe weather.
Population plays a significant part in all of this because it determines the extent of human activity that generates the consumption of energy, which produces the greenhouse gases.
for example, the above diagram depicts the possible growth curves of population. Bongaarts estimates that the medium growth projection will be accompanied by a doubling of CO2 emissions by 2025, and then another doubling will happen by 2100. But net emissions depend on other factors as well, such as GDP per capita, energy intensification of GDP, Carbon intensity of energy consumption, and tropical deforestation. But further population growth and economic development are expected to be the principle factors putting upward pressure on annual CO2 emission rates.
This is very apparent in the case of Less Developed Countries (LDCs). In 1985 LDCs were responsible for 36% of global emissions, this is expected to increase to 55% by 2025. 48% of this increase is directly related to population growth as opposed to the global total of 35% (Bongaarts, 1992). There is a definite need for a reduction in emissions but the More Developed Countries (MDCs) are the only ones in a position to do so. This is because the LDCs will experience continued population growth and expected economic development that will propel their emissions above those of the MDCs. Furthermore, the longer reductions are delayed the greater the global warming will be, as control measures aimed solely at the MDCs will become less effective over time, because the ratio of people living in the MDCs to LDCs is currently 1:4, and it is expected to shift to 1:7. But the LDCs can adopt policies to reduce their population growth, as these should be a part of comprehensive international drive to reduce global warming.
In order to reduce our emissions we can also try to reduce our consumption. However, the World Energy Council (WEC) projects that the world energy consumption, despite high rates of declining energy intensity assumed for all regions, will continue to increase in all major regions throughout the twenty-first century (Gilland, 1995). The maximum prediction estimates a rise in energy consumption of MDCs from 5.9 Gtoe (gigatons of oil equivalent) in 1990 to 8.0 in 2020, and a rise for LDCs of 2.9 Gtoe to 10.3 Gtoe (Gilland, 1995).
This demand will be met predominantly by the combustion of fossil fuel. This is because nuclear power has political issues, hydroelectric and traditional biomass have physical limitations, and new renewable sources such as solar are still prohibitively expensive. This will add to the atmospheric reservoir of CO2, intensifying the greenhouse effect. In fact human activity has been responsible for increasing the CO2 concentration from 280 ppm in 1750 to 354 ppm in 1990, and we are currently at a situation where this is increasing by 1.6 ppm each year (Gilland, 1995). But Gilland also mentions that anthropogenic sulfur emission has a cooling affect, and this may offset some of the affects of increased concentration of CO2 in the atmosphere. Consequently there is still not enough information on which to base an adequate conclusion, and Gilland believes that if CO2 emissions increase and induce global warming it is simply the “part of the price to be paid for the fossil energy bonanza that has culminated in the affluent society.”
This raises the question of responsibility, who is generating the harmful emissions? Is it the more developed countries through their much higher consumption, or is it the less developed countries with their rapid population growth? Ehrlich and Holden developed a formula to attempt to answer this question: I = PAT, where I is the environmental impact, P is population, A is affluence, and T is technological efficiency (MacKellar, 1995). But there are problems concerning the omission of interactions between variables, the choice of variables, and interpretations. The later point is particularly important, as Malthusians would argue that as population increases, affluence declines, and this would impede technological progress. In contrast optimists postulate that an increase in population would stimulate an increase in knowledge that would enable a continued increase in affluence. But there is also the modernist view that says as affluence increases population declines and this leads to an increase in technological efficiency. Furthermore, this decomposition approach contains an arbitrary element, depending as it does on the demographic unit of account.
The I=PAT formula selects the individual as the demographic unit. MacKellar points out that if one were to consider households (I=HAT) and their subsequent economies of scale, one finds a very different allocation of responsibility between demographic and economic factors. This is because the size and rate of growth of populations are of less concern than the number and rate of growth of households to goods that are related to the household.
Changes in average household size result from the combined evolution of age-specific household headship rates and the age structure of the population. Between 1950-1990 the developed countries experienced a decline in average household size from 3.6-2.7. Mackeller identifies three reasons that explain this decline in extended families. The first is demographic, as residence in an extended family unit must necessarily decline along with fertility for the simple reason that there are fewer kin to live with. The second is sociologic, explaining this shift to be the result of an exogenous shift in taste towards privacy. The last is economic and relates to income and the price of housing. The less developed countries had marginal change in the same time period dropping from 5.0-4.8. Individually there were mixed results, but the main cause of change is the decline in the age specific headship rates. So there is a shift towards atomized living in the developed countries accompanied by a decrease in the extended family in developing countries resulting from changes in the age structure. This means that there are more households. Furthermore, modernization will reduce average household size in LDCs, because as they increase their material standard of living, allocation of resources is easier, and some form of social security may develop.
This is important as it relates to the significance of using I=PAT or I=HAT. I=PAT calculates that for both LDCs and MDCs a third of the growth of energy consumption is accounted for by demographic growth. Whereas I=HAT has LDCs staying more or less the same, but for MDCs the amount has grown to three-quarters. In terms of annual global emissions I=PAT has 18% attributed to demographic growth, compared to 41.1% with I=HAT. MDC behavioral patterns, in the form of increased nucleated living arrangements, are an important contributor to the growth of energy consumption, which will emit more greenhouse gases into the atmosphere, strengthening the greenhouse gas effect. So the I=HAT is a stronger proponent for curbing population growth, especially as the LDCs will have number of households growing faster than the number of people.
However, the relationship between fertility decline and future environment impact is not straightforward. While a reduction in fertility will result in a decreased rate of population growth, causing less environmental impact. It will at the same time generate an ageing of the population that will increase the high age specific household headships, increasing the environmental impact. So there is a clear need for more information concerning the nature and impact human activity has on the environment. Once we can obtain such information MacKellar suggests that the formula can be expanded to look like: I = c + aPAT=bHAT where c is the constant, and a and b are the respective weights of individuals and households.
These three articles make it clear that Global warming is (if it hasn’t already) going to take place in some form or another. But there is still not enough known about the various factors and their complex interactions that would enable us to determine to what extent this will happen. In any case population is a key factor, and it is set to increase through trends already established, generating an increase in demand for energy consumption, that will result in more emissions of CO2, exacerbating the greenhouse affect and the extent of global warming. Consequently there is a definite need for international action to minimize the extent of global warming. It is in everyone’s interest, as along with the environment impacts of global warming, the price of fossil fuel will increase making it more difficult for LDCs to raise their standard of living. But it will be very hard for LDCs to directly reduce their emissions, as it will affect their economic growth. Maybe we will have to satisfy ourselves with policies that stabilize MDC emission levels, and reduce population growth rates in LDCs, and resign ourselves to life on a warmer planet.
I have neither given nor received any unauthorized aid in the writing of this paper:
References:
John Bongaarts, "Population Growth and Global Warming" in Population and Development Review, Vol. 18, No. 2, June 1992, pp. 299-319.
Bernard Gilland, "World Population, Economic Growth and Energy Demand, 1900-2100" in Population and Development Review, Vol. 21, No. 3, September 1995, pp. 507-540.
MacKellar, F. Landis, W. Lutz, C. Prinz and A. Goujon, "Population and Households, and CO2 Emissions", Population and Development Review, Vol. 21, 1995, pp. 849-865.
The United States Environment Protection Agency’s homepage for Global Warming: http://www.epa.gov/globalwarming/climate/index.html