Climate variability

Climate variability increases internal migration in South America and swollen cities


As global climate change affects livelihoods across the globe, migration patterns are also changing. In a recent study published in Global environmental change, Clark Gray, Valerie Mueller, and I have found that since the 1970s, climatic variations have increased internal migration in many countries in South America, with few exceptions. And a lot of people are heading to the cities.

Using The data From 25 censuses conducted in eight countries between 1970 and 2011, we found that above and below average temperatures were associated with an overall increase in the likelihood of migration between provinces. We focused on migration among adults aged 15 to 40, the ages when migration is most common, who did not cross international borders. By relating this data – over 21 million observations in total – to historical climate records, we could apply statistical models to estimate the association between temperature and precipitation variability and the probability of migration between provinces, by controlling a set of other factors that may have migrations affected.

Abnormal cold month increased odds of emigration by eight percent

Each month that mean temperatures were two or more standard deviations above normal – a low probability event – the odds of emigration increased by 3% on average in the study countries: Argentina, Bolivia, Brazil, Chile , Colombia, Ecuador, Paraguay, and Uruguay. Comparable exposure to below-average temperatures increased the chances of migration by an average of eight percent.

We assume that these models may reflect the disruptive effects of abnormal temperatures on agricultural production and agriculture-dependent economies in the region. We did not identify such mechanisms in our data, but this hypothesis is consistent with the evidence that both cold and warm temperatures reduce crop yields.

In addition to these aggregate effects, abnormal temperatures had a stronger and more consistent positive effect on migration to urban versus rural destinations. We were unable to identify whether the migrants moved of rural or urban areas, and therefore could not quantify the extent to which climate variability contributed to urbanization. But it probably had some effect. And our results suggest that climate change is contributing to the increase in the overall population of some cities in South America, whether migrants come from rural or other urban areas.

The links between climate change and displacement to urban areas raises questions about the planning needs of the cities receiving these migratory flows. It also raises questions about incorporating migrants into these cities, which can be a particular challenge for people leaving rural areas, who are suddenly faced with a very different setting and new prospects for livelihood.

Demographic differences and trapped populations

The association between climate change and migration varied across demographic groups. Gradual increases in temperature increased migration among women, but not among men, and among individuals who did not complete primary school, but not among those who did.

However, exposure to more extreme temperature changes – when monthly temperatures were two or more standard deviations above or below the mean – had significant positive effects on migration among all groups. Differences in climatic effects between groups are apparently more a matter of degree than nature.

In Bolivia, we see evidence of ‘trapped’ populations

Finally, the analysis of how the climate affects migration in each country revealed a major exception to our overall findings. In Bolivia, higher temperatures have been associated with decreases migration, the opposite of what we have found in other countries. This “trapped population” dynamic has been observed somewhere else and is expected to be more common among the very poor. This may help explain its presence in Bolivia, where the very poor constitute a larger portion of the population than the other countries in our study.

Although we were unable to identify the particular characteristics that explain the different outcomes between demographic groups and countries, the variability in climate-migration links is consistent with the high degree of variation in wealth, dependence on agriculture and geography across South America. Future research on these characteristics – essentially, How? ‘Or’ What the interplay between socio-economic conditions and climate change produces these results – can enable policymakers to proactively identify countries where climate-related changes in migration are most likely.

It was one of the first studies examine climate-related migration patterns in several countries using comparable data and measures. The fact that he identified significant climatic effects on migration reinforces the hypothesis that climate change will disrupt human population movements. Yet the variation in these climatic effects also underscores the need to anticipate nuances and adapt analyzes, conclusions and policy recommendations to specific contexts.

Brian Thiede is an assistant professor of rural sociology, sociology and demography at Pennsylvania State University.

Sources: Climate Change, Global Environmental Change, PNAS, University of Minnesota.

Photo credit: La Paz, Bolivia, July 2008, courtesy of flickr user Cliff Hellis.


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