Global warming as a cause: Rising temperatures draw people to cities

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As of November 2022, there are eight billion people living on Earth. In seven years, the figure is expected to be 8.55 billion, 60 percent of whom will then live in cities.

However, the cities in the rich industrialized countries are largely spared this population increase. It is the megacities of the global south that are attracting more and more people. The largest of them already have more than 20 million inhabitants. For example, Delhi in India with 31 million or Dhaka in Bangladesh with 22 million. By 2030, Delhi's population will grow by another 25 percent, and Dhaka's by as much as 29 percent. Delhi will then be home to more people than Tokyo, still the world's largest city with 37 million inhabitants. In 2030, Tokyo will have two percent fewer people.

For some time now, population researchers have been observing a correlation between rising earth temperatures and population growth in the cities of developing countries. The poorer a country, the greater the influx from rural to urban areas. Until now, the motives have been unclear: whether it is the flight from rising temperatures that drives people to migrate to the metropolises, whether it is generally the attractiveness of large cities that draws people, the promise of a better life, or whether it is entirely different factors.

Global warming as a starting point

That it is indeed global warming that is driving urbanization has now been demonstrated by Marc Helbling and Daniel Meierrieks of the Social Science Research Center Berlin (WZB). "We focus on global warming because the persistent rise in temperature is the starting point for a broader range of similarly persistent phenomena associated with global climate change," they write in their publication.

For their analyses, Helbling and Meierrieks used state-level temperature data for 118 states between 1960 and 2016, which they linked to national urbanization rates.

The authors assumed an increase in all urban dwellers from 33 to 59 percent of the world's population during the study period. But in cities in hot climates, the proportion of urban dwellers tripled. This was the case in Nigeria, where only 15.4 percent of all inhabitants lived in cities in 1960, while by 2016 this figure had risen to almost half. At the same time, the average annual temperature in the already warm climate zones rose by around one degree during this period, in Nigeria from 26.8 to 27.8 degrees.

Crop failures and diseases cause rural exodus

It is primarily the decline in agricultural production that is causing people to leave their lands. And this is a consequence of global warming.

This is because the reason for lower harvests is, for example, water stress, which impairs plant growth and promotes the spread of plant pests. However, crop failures caused by isolated heat waves, extreme rainfall or natural disasters also contribute to the rural exodus. But ultimately, the slow, steady warming of the climate far outweighs the migratory movements triggered by short-term events.

Rising temperatures, however, also make people sick. They increasingly suffer from heatstroke, cardiovascular diseases, difficulties during pregnancy, exhaustion and infections due to the spread of pathogens and disease vectors, such as insects and rodents. Patients then have to make their way with accompanying relatives to the cities, where they are more likely to find help from doctors and in hospitals than in their villages.

Social scientists refer to all of these as "push factors," circumstances that drive people from their ancestral homelands.

Metropolitan "pull factors" that attract people include opportunities for wage employment, access to health care, shorter commutes, and comparatively low transportation costs.

Pull factors of the cities

This is because the diverse urban economy can tap directly into the reservoir of the often underemployed or "surplus" rural labor force by offering higher wages and thereby fueling greater immigration to urban areas.

However, this migration also entails that the provision of public infrastructure or health services in rural areas shrinks even further, especially when there is a lack of resources to expand public goods due to declining productivity.

Often, people end up in the growing slums. But life there does not deter them. Apparently, the advantages that the city offers them outweigh the misery of having to live in precarious housing.

Such a development is not without consequences. Global warming could also undermine the social stability of societies, the authors say. There is sufficient evidence, they say, that higher temperatures encourage aggression and violent crime and facilitate civil wars. Add to that economic discontent and increasing resource scarcity, such as the disappearance of arable land. Thus, the desire for security would be another push factor for living in cities, where people hope for protection through police presence.

Unlike usual for scientists, Helbling and Meierrieks also derive policy advice from the results of their study. In addition to rapidly reducing greenhouse gas emissions, they suggest improving access to public goods in rural areas, especially in the very poorest economies. Richer countries would be well advised, the researchers say, to support such measures through increased development and technology assistance. This is also to curb international migration from poor to rich countries. After all, the metropolises in the global south are also important hubs for international migration.

(jle)