United States as a costal nation: why is America inherently richer than Africa?

Why is America inherently richer than Africa? Jeffrey Sachs will say geography. Most rivers in the United States are navigable to oceans, while in Africa rarely they are. Whether you have access to oceans determines your income level, Professor Sachs argues.

In his research paper “The United States as a Costal Nation”, he finds that “US economic activity is overwhelmingly concentrated at its ocean and Great Lakes coasts”.

In another research paper "Climate, Water Navigability, and Economic Development", he discovers that “Temperate ecozones proximate to the sea account for 8 percent of the world’s inhabited land area, 23 percent of the world’s population, and 53 percent of the world’s GDP. The GDP densities in temperate ecozones proximate to the sea are on average eighteen times higher than in non-proximate non-temperate areas.”

Thanks to geography, the narrow band of costal regions of Africa are still more affluent (or more accurately, less poor) than inland. But because of the lack of rivers navigable to oceans, Africans who unfortunately were not born in costal regions may not have the luck of benefiting from oceans. In the United States and Europe, in contrast, as shown by the map, “ocean access” are almost universal, even in deep inland area.

References:

The United States as a Coastal Nation (PDF file)
Jordan Rappaport and Jeffrey D Sachs
Abstract: US economic activity is overwhelmingly concentrated at its ocean and Great Lakes coasts, reflecting a large contribution from coastal proximity to productivity and quality of life. Extensively controlling for correlated natural attributes and initial conditions decisively rejects that the coastal concentration of economic activity is spurious or just derives from historical forces long since dissipated. Measuring proximity based on coastal attributes that contribute to either productivity or quality of life, but not to both, suggests that the coastal concentration derives primarily from a productivity effect but also, increasingly, from a quality of life effect.

Climate, Water Navigability, and Economic Development (PDF file)
Andrew D. Mellinger, Jeffrey D. Sachs, and John L. Gallup
Abstract: Geographic information systems (GIS) data was used on a global scale to examine the relationship between climate (ecozones), water navigability, and economic development in terms of GDP per capita. GDP per capita and the spatial density of economic activity measured as GDP per km2 are high in temperate ecozones and in regions proximate to the sea (within 100 km of the ocean or a sea-navigable waterway). Temperate ecozones proximate to the sea account for 8 percent of the world’s inhabited land area, 23 percent of the world’s population, and 53 percent of the world’s GDP. The GDP densities in temperate ecozones proximate to the sea are on average eighteen times higher than in non-proximate non-temperate areas.