When discussing the socioeconomic effects of climate change, little attention has been given to the role of the ocean. This column presents new evidence of the effect of ocean acidification on early-childhood mortality in low- and middle-income countries. Small increases in exposure to water acidity while in utero have significant effects on neonatal mortality. A closer look at possible mechanisms highlight the role of the ocean for nutrition and how overfishing represents an additional threat.
Climate change, together with industrial and habitat-destructive fishing, pollution, and coastal urbanisation, has led to a sustained decrease in fish stocks over the last decades. With more than three billion people depending on marine biodiversity as a major source of food, understanding the consequences of human activity on the ocean is crucial for global food security.
This is particularly relevant for low- and middle-income countries, as their populations are heavily reliant on fish for nutrition. Across the globe, fish represents 17% of all animal proteins that are consumed. In low- and middle-income countries, this percentage reaches an average of 26%, with peaks of 50% or more in Southeast Asia and in small island developing states.
While a large body of evidence on climate change describes the socioeconomic consequences of atmospheric events inland, the impact of what is happening offshore has received little attention. Anthropogenic emissions of CO2 are transforming the ocean. Water acidity has been increasing since the Industrial Revolution – a phenomenon known as ocean acidification. In addition, global sea surface temperatures have risen, and the ocean’s oxygen content has dramatically decreased.
While all these factors are central for marine life, knowledge about the overall effect of climate change on fish stocks is still limited. Growing evidence, especially archaeological, points to a decrease in fish survival.
Coastal communities in developing countries have few nutritional alternatives. The consumption of macro- and micronutrients contained in fish is essential. These can be especially vital during pregnancy because nutrient deficiencies can contribute to fetal growth restrictions – the main cause of neonatal deaths.
Our recent study tests this hypothesis on a global scale by focusing on ocean acidification. We study how in utero exposure to varying levels of ocean acidification in the closest waters influences early-childhood mortality and development in low- and middle-income countries. By homogenising information from the Demographic and Health Surveys, the study focuses on more than 1.5 million live births between 1972 and 2018 across 36 developing countries in Africa, Asia, and Latin America.
The ocean’s acidity significantly affects neonatal mortality – the probability that a child will die during their first month of life. An increase in 0.01 units in the ocean’s acidity while in utero increases neonatal deaths by approximately two deaths per 1,000 live births in communities living near the ocean’s shore. The size of this effect is nontrivial if we consider that a 0.01 change in acidity is equivalent to roughly one-sixth of the average increment in acidity experienced by sampled areas from 1972 to 2018, or just 3% of the predicted increase by the end of the 21st century by the Intergovernmental Panel on Climate Change (2013).
Rather than persisting over time, this effect gradually decreases beyond the first month of life. Among living children, those that experienced higher acidity in utero tend to have better anthropometrics and a lower probability of morbidity. However, no effect on contemporaneous nutrition indicators is recorded. These results suggest that ocean acidification leads to death harvesting among children, such that mortality is more prevalent among the weakest children.