Most environmental problems, including those arising from climate change, are aggravated by population growth. Thus, the fact that the world's population has surpassed 6.7 billion and continues to grow by some 78 million additional people each year presents enormous challenges.
Where women control their own bodies and have access to reproductive health, they tend to choose smaller families. However, in poor countries some 200 million women would like to delay their next pregnancy or stop having children altogether - but because of gender inequality or lack of access to information or services, they can't do that.
Efforts to empower women, improve social conditions and ensure universal access to reproductive health, including voluntary family planning, would all help to reduce fertility and contribute to eventual population stabilization. Support in these areas is most critical in the poorest countries, where rapid population growth combines with poverty and lack of access to resources to exacerbate local environmental degradation and resource depletion and to inhibit sustainable development.
Distinct populations groups and patterns of living clearly impinge on the environment in different ways. Age structure, household size and spatial distribution - and most important, level of development - all affect per capita emissions, and must be integrated into climate change modeling. For the most part, countries with high rates of poverty and population growth contribute relatively little to greenhouse gases and other irreversible global ecological threats. This is not always taken into consideration in looking at the effects of population growth on greenhouse gas emissions, for instance in the IPCC Special Report.
In the long term, lower fertility in low-income countries will result in some reduction of global greenhouse gas emissions. However, lower fertility usually is associated with economic development, including urbanization. Unless low-income countries follow new, low carbon paths of development, higher standards of living will lead to higher per capita greenhouse gas emissions. The usual trend toward smaller household sizes as development proceeds will also tend to increase per capita emissions for a given population size.
Further, 'population momentum' in countries with a large proportion of young people will result in continued high growth rates despite declines in fertility. Even as fertility declines significantly, population growth will continue for years to come.