The topic was only barely on the table at Fourth Conference of the Parties, but the issue of the fairness of current greenhouse-gas emissions patterns hovered over the recently completed negotiations in Buenos Aires.

The nature of the commitments agreed to in 1997 in the Kyoto Protocol obscured the point, but it really isn’t so much nations – the size of which may be accidents of history, geography and demography – that emit greenhouse gases. It is human beings, living real lives, and possessing a framework of individual rights that has not yet evolved to capture this increasingly important one: the right to use the global atmosphere in ways that do not jeopardize the environment or other human beings.

Some human beings today send dozens of times their own body weight in carbon into the atmosphere, and take for granted their right to keep doing so, despite the impact of these emissions on other human beings who may send skyward less than their own weight. But as climate change becomes a more urgent public issue, and as governments face the need to shrink the global emissions total, more attention is likely to focus on the vast disparities in per capita emissions of carbon dioxide and other greenhouse gases.

One of the ironies of this change of focus will be an increase in interest in the impacts of different population futures on the goal of slowing human-induced climate change without impoverishing humanity. Indeed, the critical link between population and climate change can only be addressed from a perspective of equal access to the carbon-cycling properties of the atmosphere. Absent such perspective, population’s role in climate change tends to be obscured by the yawning gap between high and low per-capita emitters of greenhouse gases. There seems little scope for considering population’s role in future climate change while the industrialized countries, whose populations are growing relatively slowly and represent only a fifth of the world’s total, contribute two-thirds of all greenhouse gas emissions.

Linked to the key concepts of climate sustainability and atmospheric equity, however, population trends emerge along with technological innovation as the greatest source of hope that humanity may actually succeed in resolving the problem of climate change before catastrophic ecological change has occurred. To illustrate this key point and to demonstrate the importance of per capita emissions to understanding climate change, Population Action International released in Buenos Aires an update to its 1994 climate report (Stabilizing the Atmosphere: Population, Consumption and Greenhouse Gases, excerpted in Tiempo No. 16, June 1995). The new report, Profiles in Carbon: An Update on Population, Consumption and Carbon Dioxide Emissions, features a nearly half-century record of the per-capita CO₂ emissions of 179 countries, most of which are also ranked graphically by their 1995 emissions. The disparities in per capita emissions are vast indeed, demonstrating the impact unequal consumption patterns have on atmospheric change. According to PAI’s analysis, 20 percent of the world’s population is responsible for 63 percent of CO₂ emissions, while another 20 percent is responsible for only 2 percent of these emissions. This inequity correlates to some degree with per capita income and is similar to inequalities in wealth identified recently by the United Nations Development Program in its Human Development Index.

Those populations with the most financial and technical resources to adapt to climate change are disproportionately putting at risk other populations who lack these resources – and who are scarcely contributing to the problem, if at all. The situation is even less just given recent predictions that agriculture in the temperate latitudes may experience few serious impacts from climate change, while farmers in the tropical latitudes of the developing world may face significant challenges in food production. Climate change "winners" are considered likely to be the most northern populations of North America, Europe and Asia, where only a tiny fraction of the world’s 5.9 billion people live.

Consider the estimate of the Intergovernmental Panel on Climate Change that global carbon emissions would need to be cut by at least 60 percent to stabilize CO₂ concentrations at roughly current levels. This suggests that, based on 1995 CO₂ emissions and population data, 2.55 billion human beings living in 69 countries emitted so little carbon dioxide on a per capita basis they essentially were helping to bring the atmosphere into balance. These people were hardly compensated for their global good citizenship, and in fact they were living in poverty in close correlation to the magnitude of their contribution.

These figures do not include emissions from biomass burning and land-use changes because of a lack of comparable country data. No doubt the full picture would reduce the proportion of "under-emitters" relative to "over-emitters" to some extent. Fossil fuel carbon is fundamentally different from that found in trees and soils, however, in one important respect: It was accumulated over hundreds of millions of years and buried securely underground. Once it is in the atmosphere – or in plants, soils and oceans – it will never be locked away so securely again.

In any event, the point remains the same. One of the best arguments against voluntary emission commitments by non-Annex I countries (a major topic of discussion in Buenos Aires) is this: Such commitments could result in long-term limits on per capita emissions that, even if generous by the country’s historical standards, would condemn its citizenry to second-class status in using the world’s fossil fuel reserves. And these are arguably the natural resource most associated, in today’s world, with prosperity. What government would agree to that?

Much more likely, eventually, is a climate agreement that drives global emissions reductions through incentives based on the equal human right to use the atmosphere. This could take the form of government-to-government tradable emission permits based on the per capita emissions of trading partners. Both the benchmark for trading and the price of trades could be set by international agreement, through a process that would reflect public perceptions of the urgency of climate change and political will to address it. The goal would be to bring global emissions as close as possible to agreed-upon ceilings aimed at stabilizing atmosphere and climate, respecting equal human rights to use the atmosphere.

Where human population goes as climate change unfolds, however, will make a huge difference to how generous individual emissions allocations will be in the coming centuries. The good news is that, contrary to the assumptions of many analysts in the climate change field, the range of possible population paths in the 21^st and 22^nd centuries is wide indeed. Whether world population doubles or triples yet again or peaks by the middle of the next century depends in large part on policies and programs that governments put into place today. All the world’s governments agreed on the principles and strategies governing these policies in 1994 at a historic international conference on population and development held in Cairo. All action on population, the nations agreed, should be grounded in human rights and the free and informed decisions that individuals and couples make about their childbearing. In particular, population policies and programs consist of social investments in human development – especially improved access to family planning and related health services, to education for girls, and to economic opportunities for women.

Global population policies are thus founded on the same basic principles of human rights and fair opportunities for development that governments are struggling to respect while addressing climate change through the Framework Convention on Climate Change and the Kyoto Protocol. If governments follow through on the commitments made in Cairo in 1994, the future of world population change could resemble the United Nations long-term low population scenario, which extends to the year 2150. Intriguingly, this curve somewhat resembles another curve representing a global carbon dioxide emissions path that would be needed to stabilize atmospheric CO₂ concentrations at 450 parts per million by volume, just under a doubling from pre-industrial times. This path was proposed by T. M. L. Wigley, R. Richels and J. A. Edmonds in Nature in January 1996.

If one converts the historic and proposed global CO₂ emissions path to comparable per-capita emissions paths based on the full range of UN population scenarios, the result is instructive. If population follows the high path, growing to 27 billion people by 2150, the resulting global per capita emission capable of stabilizing atmospheric carbon in that year would need to be held to the level of per capita carbon emissions in the middle of the 19^th century. Under the low population projection, by contrast, with world population peaking around 7.7 billion and then gradually declining to 3.6 billion in 2150, the climate-sustainable per capita emission amounts to what it was just prior to World War II. The figure would actually be growing in the first half of the 22^nd century, as world population gradually declined in the context of a relatively stable global ceiling on emissions.

Obviously a transformation of energy use from waste to efficiency and from carbon to non-carbon sources will need to occur between today and 2150, regardless of feasible demographic change. Just as clearly, the challenge this transition poses will be eased by a lower rather than higher population trajectory, and that difference could prove critical to the global environment.

In recent decades the Law of the Sea established a key principle: All human beings share an equal right to use the common property of humankind. Surely the atmosphere is such a global commons. Ultimately, the world’s governments will need to recognize that long-term efforts to slow climate change will depend on a fair allocation of that right based on per-capita, much more than national, emissions of greenhouse gases. Once governments come to this realization, they are likely to reassess the priority of another historic agreement: the Programme of Action agreed to at the International Conference on Population and Development in 1994.

That agreement provides a road map to a stable or even gradually declining population in the next century, based on the healthy childbearing decisions of free and informed couples and individuals. It also points the way to a world in which all human beings have access to the global atmosphere for modest emissions of greenhouse gases that could continue indefinitely into the future without adding to the risk of human-induced climate change.