In Tubb's model, workers and retirees, who both value environmental quality and consumption in youth and old age, diverge in their policy preferences. Since the workers and the retirees want different policies, the outcome is determined through the political process. Political parties converge in platforms that try to maximise the best outcome for the whole electorate. Yet, since the old are always the minority, the policy preferences of the older generation will, therefore, have no impact on political outcomes if age is the only determinant of policy choices.
The model is backed empirically by government environmental expenditure data for 47 low, middle and high-income countries of various social, political and institutional differences between 1970-2007. For about 95% of the countries in this sample, which was sourced from the UN, increases in longevity positively impact on environmental protection expenditure. Tubb found the demand for public spending on the environment is positively related to per-capita income beyond a threshold of about US$20,000 (calculated at 1990 rates).
"This an economy-wide result, so when a country's average income per person rises above that threshold level, national governments are more likely to spend public funds on the environment – so the amount of government environmental expenditure tends to rise with average income," says Tubb. "This result is quite intuitive, since citizens as a whole tend to demand a better quality environment when the country (and its citizens, on average) becomes more prosperous."
The empirical data also shows that although the proportion of individuals in the population aged 65 years and over negatively affects public spending on the environment, this effect is counteracted by the positive impact of increases in longevity and the proportion of the population aged between 15 and 64 years.
Elisabetta Magnani, an economics professor at the Australian School of Business, says research is trying to understand what synergies and obstacles may emerge with population ageing and environmental change. "One factor is pushing spending on the environment up, another down. There is a net effect shown here. Ultimately, it is clear that population ageing may not be such an obstacle to government investment in environmental protection," she concludes.