Where will People live by 2025?

How will the world’s population distribution change by 2025? Here is an interesting take:

This projection, dubbed “Mapping the Future,” shows that the greatest increases in population will occur in developing countries. Of course, this projection might be wrong, but this one has been built by watching nine million ‘cells’ distributed across the globe. And the researchers also have mapped several other evolutions, including maps of countries which will be touched by a lack of water or a growth in emission of carbon dioxide.

Here are some excerpts from this Earth Institute at Columbia University news release.

The map indicates that the greatest increases in population density through 2025 are likely to occur in areas of developing countries that are already quite densely populated. In addition, the number of people living within 60 miles of a coastline is expected to increase by 35 percent over 1995 population levels, exposing 2.75 billion people worldwide to the effects of sea level rise and other coastal threats posed by global warming.

You can download this full map from this page at CCSR, but be warned. This map is in PDF format and “weighs” 34 MB.

Below are two small images extracted from this map. The blue-ish colors represent losses of population per grid cell between 1995 and 2025 while yellow-ish colors show gains. As you can see, parts of Eastern Europe will see a decrease in population. (Credit: CCSR)

European population evolution between 1995 and 2025

On the contrary, you can see that the population in Asia will continue to grow at a fast pace. (Credit: CCSR)

Asian population evolution between 1995 and 2025

But how these maps were built? And how did the researchers arrive at the projected population gain or loss for each grid cell? Here are some answers.

First, [the researchers] took two maps of past population density called the Gridded Population of the World, which represent density in 1990 and 1995. These maps […] show population density in nearly 9 million grid cells at two different times in the 1990s.

They can also be compared to show changes in each grid cell between 1990 and 1995. These changes can then be extended to 2025 for each grid cell and adjusted so that all grid cells within a specific country added together are equal to the projected population under the United Nations Population Division’s medium projection of population for 2025.

Thus the maps shown here reconcile two very different sets of data: a detailed map of population distribution in the recent past by small grid cells, and a population projection made for a future date and for entire countries. The adjustment necessary for each cell is more complicated than it might seem, however. Given the diversity of population change between 1990 and 1995, there’s no easy or obvious way to bring all the grid cells smoothly to the point where a nation’s population equals the total that UN demographers project for 2025

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