Arrow et al (2004: Table 2) estimate how much ‘genuine wealth per capita’ (including natural capital, human capital, and manufactured capital) changed during 1970-2000. The estimates are necessarily approximate, but they have been made carefully and the results are instructive. They find that while GDP per capita grew quite rapidly during 1970-2000 in all regions except in sub-Saharan Africa, rates of growth in ‘genuine wealth per capita’ were far lower. They _declined_ sharply in sub-Saharan Africa and in the Middle East and North Africa (by -2.6 and -3.8 percent per year respectively). They grew very slowly (well below 1 percent per year) in South Asia and the United States. They grew rapidly only in China, due to its low population growth and heavy investment in productivity. Revising the method to include more information on growth in human capital and institutional change, Dasgupta (2010: 9-10) derives far lower estimates of growth in genuine wealth per capita for China 1970-2000, and for South Asia he estimates a _decline_ of between -0.4 percent per year (India) and -1.4 percent (Pakistan).

Human ingenuity has faced an uphill task at devising ways of managing common property resources ─ given the institutional and political challenges posed in aligning divergent interests. Markets are very poor at incentivizing people not to overuse resources that are unpriced or under-priced relative to social cost (Arrow 1969, Dasgupta 2001, Stern 2006), especially in the case of transnational common resources (Dasgupta et al 1997). The consequent negative externalities need to be addressed through collective action, but in the absence of strong mechanisms for mutual coercion it is very difficult to align the interests of different stakeholders to this end. Ostrom (1990) has argued that common property can be successfully managed by user associations in small communities if eight ‘design principles’ are met, including the ability to effectively exclude unentitled parties. Such conditions clearly do not apply to global common resources. As Lee (1990:317) points out ‘each birth inflicts costs on all others by reducing the value of their environmental birthright’.<sup>2</sup> The juxtaposition of all these scientific, executive, and political challenges places high demands on national and global institutional capacity, as evidenced by the slow progress made in decades of efforts to regulate carbon emissions. The original projections of the _Limits to Growth_ study for the period 1970-2000 correspond broadly with the observed trends during this period (Turner 2008, 2012).

# **_1.2  Managing Climate Change: addressing per capita emissions_** **<u>and</u>** **_population_**

Models of climate change take population size into account, but typically treat it as a given (for example, Stern 2006; Nordhaus 2008, 2012). They tend to use the United Nations medium variant population projections. Using this approach, the World Bank (2010: Figure 3.5) estimates the impact of climate change on the growth in agricultural productivity required to meet rising food demand. The model incorporates projected rises in food demand due to growth in incomes as well as in population size, and shows how much harder it will be to meet that demand given anticipated climate change. A huge increase in agricultural productivity backed by greatly intensified regulation to protect natural systems will be needed.

Yet population size _is_ amenable to policy, as we discuss below, and makes a big difference to the size of adjustments required on other fronts. Models vary, but the World Bank (2010) estimates that to meet the growing demand for food between 2005 and 2055, agricultural productivity will need to rise by 64 percent under the assumptions of the ‘business as usual’ 4