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The IPCC itself has partially assessed the topic, concluding that population growth, urbanization, and changes in age structure are important drivers of emissions. It has also concluded that demography shapes the exposure and vulnerability of pop ulations to climate impacts and can limit, or facilitate, the ability of society to adapt to those im- pacts. What is missing is an account- ing of how reductions in population growth might play a role in responses to the climate issue (see supplemen- tary materials). Many in the climate policy commu- nity currently focus on achieving sub- stantial emissions reductions in the near future. Although slowed popula- tion growth would contribute only mod- estly in the short term, its cumulative effect over the 21st century would be sub- stantial. Slowed population growth would reduce emissions and the demand for energy that would have to be satisfied with low- or zero-carbon sources. It would therefore also have an important effect on the scale of the energy system ultimately required under a stabilized climate.

MISPERCEPTION 4: POPULATION POLICY IS TOO CONTROVERSIAL TO SUCCEED

Family planning programs have attracted criticism since their initiation. The most persistent opposition has come from con- servative religious and social groups. One of their main concerns is that making con- traception readily available encourages promiscuity and leads to a breakdown of family life. In addition, the Catholic Church opposes artificial contraception, and Islam opposes sterilization. These religious con- cerns are shared by conservative political allies, leading to frequent controversy . Other concerns about family planning programs have been raised by human rights advocates who fear coercion. They point to examples of massive abuses by the Chinese government during the implementation of the one-child policy and by the Indian gov- ernment during an emergency period in the late 1970s. These abhorrent practices were and are universally condemned. Neverthe- less, reproductive health remains a political issue in many countries, and constraints on women’ s choices continu e to exist (e.g., lim- ited choice of contraceptive methods or lack of services). A key point of sensi tivit y is that famil y planning programs largely aim to reduce fer- tility in the developing world while people in the developed world, which is primar- ily responsible for causing the climate to change, continue their excessive emission of greenhouse gases. At the same time, many developed countries are also increasingly concerned about aging and decline of their populations. Many in the climate change community believe that entering into a popu- lation policy discussion thus blames the poor countries for problems created by the rich countries. Although this belief is real, it does not change the fact that population growth in developing countries poses challenges for climate and development and deprives the international community of an important policy lever to improve human welfare. Although these controversies do indeed exist, they are not the obstacles to program implementation that some in the climate community believe them to be. Govern- ments around the world now support the conclusions of the ICPD, confirmed by the SDGs, which call for a human rights– based approach and for women everywhere to have the right to freely choose when and how often to get pregnant (

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). Many countries in Asia and Latin America have invested in family planning programs, and increasing numbers of governments in sub- Saharan Africa have started such programs. There is widespread agreement among gov- ernments and international organizations that family planning programs are a valu- able investment. The SDGs in fact call for more such services. But these programs are often given low priority because they are considered a health investment rather than an investment with wide-ranging socioeco- nomic and environmental benefits.

POLICY LEVERS

Rapid population growth is one of the key drivers of emissions and one of the determi- nants of vulnerability to impacts; it therefore should be considered as a potential climate policy lever. A key first step in remedying the current neglect of the issue is for the IPCC to include population policy in its assessment of the literature on mitigation and ad- aptation options. Although the outline for the sixth IPCC assessment report has already been agreed upon (with no explicit mention of population policy), there is ample opportunity within its structure to assess literature on popu- lation policy as a component of mitiga- tion or adaptation responses, as well as its costs and benefits, implementation barri ers, and links to SDGs (see supple - mentary materials). The IPCC should also consider the inclusion of more so- cial scientists experienced in reproduc- tive health and population policy . Beyond the IPCC, the climate and environmental communities and in- ternational development institutions should embrace scientifically sound analyses of population policy and hu- man rights–based reproductive health pro- grams. Other international environmental assessments (

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,

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) have done somewhat bette r than the IPCC in cover ing this topic . Given the urgency of addressing climate change, all available options, especially those that have multiple benefits for sustainable development, should be assessed by experts and considered by governments.

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SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/361/6403/650/suppl/DC1

10.1126/science.aat8680

1 9 5 0 1 9 7 5 2 0 0 0 2 0 2 5 2 0 5 0 2 0 7 5 2 1 0 0

P o p u l a t i o n s i z e ( m i l l i o n s )

0 50 100 150 200 250 300 350 400 Esti mate s Proj ectio ns Pakistan Bangladesh

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17 AUGUST 2018 • VOL 361 ISSUE 6403

Population estimates and projections for Bangladesh and Pakistan

Differences suggest that a good family planning program (as in Bangladesh beginning in the 1980s) can have a large impact on population trajectories in the long term. Data are from (

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). See supplementary materials for details on data and methods.

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