This article was originally posted on New Security Beat. It is reposted here with their permission.

Featured side by side at the top of The New York Times home page recently were two stories: one on the United States and China, the world’s largest producers of carbon emissions, committing to a global climate agreement, another on how rising seas are already affecting coastal communities in the United States.

The stories reflected the immediacy of global environmental challenges – climate change being the predominant one among many. These challenges were the impetus for the Population Reference Bureau (PRB) to focus on “human needs and sustainable resources” in this year’s World Population Data Sheet, a widely used print and digital resource for the latest demographic, health, and environment data from around the world. As in years past, the Data Sheet features our latest global population projections, but there are additional indicators in the 2016 edition that underline the challenge of balancing sustainability with a growing population.

New Demographic Projections

First, the population picture: Despite an overall decline in fertility rates, our projections this year point to a world with 9.9 billion people at mid-century, about one third more than we have today. Devotees of our annual Data Sheet may notice that our 2050 forecast has been inching up over recent years. The principal reason has been slower than anticipated rates of fertility decline in many sub-Saharan African countries. The top 10 country fertility rates in the world are all in Africa, led by Niger with an average of 7.6 lifetime births per woman. Niger’s population is on track to more than triple by 2050.

Drilling down, population trends vary widely by region. Under our assumptions, Africa’s population will more than double by mid-century, gaining 1.3 billion people. Compare this to a projected gain of nearly 900 million in Asia, by far the most populous region today, and only 223 million in the Americas. Europe (including all of Russia) is actually expected to decline by 12 million people. Africa alone will account for more than half (54 percent) of the total projected population increase by 2050, while Asia will kick in 34 percent. The combined population of the 48 “least developed countries” as defined by the United Nations will double.

The global population increase is likely to come despite lower fertility rates on the whole. Rapid increases in world population over the last several decades have yielded a large number of people of childbearing age, creating what’s called “population momentum.” Most countries will continue to grow for many years even though their fertility has declined or is in the process of doing so. Thus, barring a dramatic and unprecedented decrease in fertility rates in the next few decades – particularly in Africa – the world will inevitably have billions more people.

Regional population growth disparities also relate to the global immigration challenge that is currently roiling Europe (though it is by no means confined to that part of the world). The combination of growing population and environmental pressures as well as political upheaval in certain countries and regions will inevitably prompt more people to seek better lives elsewhere. Migration statistics are notoriously unreliable, given the difficulties of tracking undocumented movements and variations in what defines a migrant. However, this year’s Data Sheet indicates that Africa has the most out-migration in relation to the size of its population, while Europe is absorbing the most migrants proportionately.

Future migration patterns may also play an important role in determining prospective population sizes of both sending and receiving countries and regions. Germany, for example, experienced the highest net migration of foreigners in its post-war history last year, at slightly more than 1 million people. For the first time, migrants from outside Europe made up the majority of Germany’s immigrants. While the region is projected to start losing population in coming decades, migration could be a significant wild card in this outcome.

Environmental and Health Dimensions

From an environmental and resource perspective, the world also faces stark regional differences. In the Data Sheet, we focused on presenting indicators with reliable data that give a broad view of how population, health, and environmental factors interact.

Generally speaking, reliable environmental and resource data are hard to obtain, often because collecting such data has been a lower priority for many countries that already have data collection challenges, or because such data transcend borders and regions, requiring a more global collection approach. In some cases, such as measuring net changes in tree cover, technical obstacles preclude accurate counts for a sufficient number of countries for inclusion in the Data Sheet.

Global carbon emissions figures, compiled by the Oak Ridge National Laboratory, were up 60 percent between 1992 and 2013 (the latest year for which reliable data are available), to 9.8 billion metric tons. A large chunk of that increase came from less developed countries, particularly China, whose total emissions rose nearly fourfold to 2.8 billion metric tons. India’s total emissions increased nearly 300 percent to 555 million metric tons.

Europe’s total emissions actually decreased over this period by 17 percent to 1.56 billion metric tons, while emissions in Canada and the United States only rose about 5 percent to 1.54 billion metric tons. Overall, 43 countries were estimated to have reduced their carbon emissions from 1992 to 2013, including notable reductions in high-income countries such as Germany and the United Kingdom. These trends and the global climate deal bring reasons for optimism about lowering future emissions levels.

Energy use is a key component of carbon emissions, and we figured that the share of energy consumption from renewable resources would help gauge how close the globe is to reducing dependency on heavily polluting fossil fuels. Note that “renewables” is a nuanced category; while it includes things like solar and wind power, it also includes hydropower, which is sometimes linked to serious environmental issues, and solid biofuels, which can include pretty much anything people burn for fuel, such as trees and bushes. As a result, many low-income countries have high renewable shares, such as Sierra Leone at 80 percent, while industrialized countries come in on the low side (eight percent for the United States). Worldwide, renewables account for 18 percent of energy consumption, according to data compiled from the International Energy Agency and World Bank.

In our rapidly urbanizing world, we also thought it was important to highlight trends related to resource use that affect public health. In the Insights section of our digital Data Sheet, we show how increasing urbanization and industrialization in developing countries has led to higher concentrations of fine particulate matter that can lodge in people’s lungs and cause asthma and other serious health problems. Middle-income countries face the biggest challenge as their industrialization process moves more quickly than their ability to manage pollution.

The global income divide comes to the fore again in a great set of data on municipal waste volumes compiled by a dedicated team of researchers running the Wasteaware data project. Municipal waste is a massive and growing public health and environmental problem, particularly in low-income countries where toxins from large numbers of uncontrolled dumpsites end up in water tables and in the air through unsorted refuse burning. While waste volumes (measured in kilograms per capita per year) tend to rise in tandem with national incomes, wealthier cities logically have more resources to devote to controlled disposal and household waste collection.

The municipal waste data underline that population numbers are not the whole issue when it comes to resource use and sustainability. In principle, having more people means resources must be managed more soundly, and funds made available to do so. Even so, many more billions of people will surely strain the planet’s ability to sustain us.

The mid-century population projection is by no means certain, but it is a warning that needs to be heeded. Is it possible to support a population of 10 billion? We hope to be prepared to answer that question.

Explore the digital 2016 World Population Data Sheet for access to more maps, data, and insights, or download the PDF.

Jeff Jordan is president and CEO of PRB. Peter Goldstein is PRB’s vice president of communications and marketing.

Sources: International Energy Agency, The New York Times, Oak Ridge National Laboratory, Population Reference Bureau, Wasteaware, World Bank.