Despite their intimate relationship, climate change and world population are still not talking to each other. The lack of meaningful dialogue has persisted for decades, with both seeming to deliberately ignore the significance, relevance and impact of the other.

With the simultaneous convening on Sept. 22 of a special session of the United Nations General Assembly marking the 20th anniversary of the International Conference on Population and Development and the UN Climate Summit on Sept. 23, this estranged relationship is now more glaring. Both gatherings are taking place within shouting distance of one another at UN headquarters in New York.

With growing concerns and uncertainties about the extent of the detrimental consequences of rapid population growth and climate change, the international community of nations convened the first World Population Conference in 1974 and the first World Climate Conference in 1979. Growing at 2 percent annually, global population increases reached a record high, doubling the world population in just 38 years. At the same time, rising amounts of carbon dioxide spewing into the atmosphere pointed to a gradual warming of the earth, especially at higher latitudes. The recommendations for action emanating from these groundbreaking conferences, however, essentially ignored each other.

Over the last four decades — despite rapid population growth, the addition of three billion people, increased global warming and international conferences on these issues — actions to address world population growth and climate change continued to run along parallel paths (Table 1).

Admittedly, the current report of the Intergovernmental Panel on Climate Change acknowledges that economic development and population growth continue to be the most important drivers of increases in carbon dioxide emissions from fossil fuel combustion. But the mitigation pathways to alleviate global warming skirt the issue of population growth and instead focus on energy, land use and human settlement, infrastructure and spatial planning.

Furthermore, a recent scientific study revisited the question of whether there is a consensus among climate scientists about the reality of human-caused global warming. The study confirmed that climate scientists not only accept the existence of global warming but also its human causation as a matter of fact over the last two decades.

Sadly, the upcoming special session of the UN General Assembly on population and development confronts neither climate change nor population growth. Instead, it is expected to narrowly focus on sexual and reproductive health and rights, especially of women. A UN resolution in 2013 reaffirmed that the special session is being held on the basis of the 1994 program of action adopted in Cairo, so there will be no renegotiation of the existing agreements contained therein. There will also be no final document issued by the special session, a move deliberately meant to preclude the reopening of negotiations on contentious issues, in particular abortion, as well as international migration.

One unfortunate outcome of the 1994 population conference was the shift in focus from the consequences of rapid population growth on development to sexual and reproductive health and rights, especially for women and girls, as well as the empowerment of women and improved education for girls. Besides downplaying a demographic rationale for population policy, the conference noted that global climate change was largely compelled by unsustainable patterns of production and consumption. Moreover, the sole recommended action concerning climate change asked governments to consider immigrants from countries, namely small island nations, whose existence was imminently threatened by global warming.

There are a number of reasons that world population growth continues to be taboo or at least sidestepped by international bodies addressing climate change and population matters.

First, actions to tackle rapid population growth are highly contentious, involving sensitive, personal matters of contraception, abortion, reproductive and sexual health and rights. While most women in more developed countries use contraception, an estimated 200 million women worldwide say that want to delay or prevent pregnancy and are asking for access to modern family planning methods. Making methods of birth control available in principle to couples is one thing; promoting, facilitating and subsidizing their access and use among individuals and couples by governmental authorities are another matter.

Second, many of those concerned about climate change, including environmentalists, climate scientists, leaders of nongovernmental organizations, politicians and journalists, are reluctant to become embroiled in controversial population issues, especially those relating to birth control and immigration. Rather than address world demographic growth and perhaps offend or, worse, alienate many of their donors and supporters, these “leaders” prefer to focus on technological fixes, which are viewed as the only appropriate and workable solutions to global climate change.

Third, a stabilized or declining population is feared by many people, especially those in finance, construction, manufacturing, farming, food processing and the military, thinking it will sap a nation’s economy and strength, inducing recession and eventually a depression. Low birth rates, especially below replacement level, are deemed a matter of national concern. For them, population growth — through natural increase and immigration — translates into more people and higher demand for goods and services, greater material consumption, additional workers and military recruits and thus higher profits. Consequently, environmental concerns, in particular human-induced climate change, are minimized as unproven and exaggerated.

Surely, world population growth is a major factor affecting climate change as all men, women and children increasingly rely on fossil fuels to support their daily lives. While reducing high rates of population growth alone would not resolve climate change, it clearly plays a critical role in mitigating its negative consequences.

In the next year, the international community will confront the challenges of climate change as it prepares for the next UN climate conference in Paris in November 2015. The time is long overdue for world leaders, scientists and other concerned citizens to hold a meaningful dialogue about the intimate relationship between climate change and world population growth.

Joseph Chamie and Barry Mirkin

Joseph Chamie recently retired as research director of the Center for Migration Studies in New York and as editor of the International Migration Review. He was formerly the director of the United Nations Population Division, having worked at the UN on population and development for more than a quarter century. Chamie has written numerous population studies for the UN and, under his own name, written studies about population growth, fertility, estimates and projections, international migration and population and development policy. He is a member of the Council on Foreign Relations and a trustee of the Migration Policy Institute. He lives in the New York metro area.

Barry Mirkin works as a consultant on population issues, having retired from the United Nations Population Division in 2009. He served the UN in the field of population and development in New York and overseas for 35 years. Among other duties, he was chief of the population policy section. Besides completing numerous studies for the UN, Mirkin has written studies in such areas as population and development policy, population aging, retirement and international migration. He received his graduate training in population and economics at New York University, the University of Geneva and Princeton University. He lives in Manhattan.