Researchers at Harvard's Center for International Development (CID) studied the relationship of climate to, and the effect of disease and agricultural productivity on the economic success of a city or region.

"Each year the World Bank publishes maps detailing national gross domestic product, and each year the maps show most of the countries in the tropics to be poor, even after years of economic and institutional reforms," said Andrew Mellinger, a research associate at the CID. "We were puzzled by the fact that the methods adopted by aid agencies did not seem to affect change in developing tropical countries."

To better understand this problem, Mellinger and colleagues Jeffrey Sachs and John Gallup used geographic information system mapping techniques to identify geographic and economic patterns in poor regions. Using detailed global population density data from SEDAC to create a map delineating countries based on their Gross National Product (GNP — the total value of all goods and services produced by a country during one year), they compared and contrasted wealthy and impoverished nations.

Using the Gridded Population of the World's five-minute by five-minute gridded sections, Mellinger estimated GNP density for each section by multiplying population density by per capita GNP, and grouped countries with similar economies together.

"We needed detailed information such as population distribution at a subnational level — SEDAC's database became the keystone of this research," said Mellinger.

By further sorting regions based on climate zones and coastal proximity, Sachs, Mellinger, and Gallup found that only three tropical economies — Hong Kong, Singapore, and part of Taiwan — were classified as high-income by the World Bank. However, every country within regions zoned as temperate had either middle- or high-income economies. (Interestingly, all of these temperate climate middle-income economies, including China, Russia and Eastern Europe, represented former or current socialist regimes.) In countries that straddle both temperate and tropical climates (like Brazil or Australia), the economic schism becomes even clearer — overwhelmingly, wealth concentrates in the temperate zones of these countries.

In 1995, the population density in Africa and South America showed similar distributions: heavily populated coastal areas and less densely populated inland areas, especially where the habitat was tropical rainforest or desert. (Images courtesy of the Socioeconomic Data and Applications Center. A new browser window will open.)

Sachs, Mellinger, and Gallup found that three significant geographic factors played roles in determining economic vitality: coastal proximity, the prevalence of infectious diseases, and agricultural productivity.

Research indicates that proximity to a coast facilitates getting products to outside markets while lowering trade costs.

But tropical diseases have longer-term effects than simply reducing worker productivity. The study suggests that since birth rates typically increase to compensate for increased juvenile deaths, women may be delaying entry to the marketplace to accommodate maturation of younger children. With less income available to the family, education for surviving children becomes a luxury rather than an expectation, which may ultimately reinforce generational patterns of poverty, said Mellinger.

Lastly, tropical soils are more fragile than temperate soils and typically subject to alternating dry and rainy seasons.

"Because tropical agricultural yields are typically low, urban populations, dependent upon food from rural areas, are lower than might otherwise be expected," said Mellinger. "With a smaller urban population, non-agricultural inventions and technology advances come to market more slowly than occurs in the highly urban populations of wealthier nations."

"Our research indicates that policy makers and aid organizations might have more success fighting poverty by improving overall health and creating non-agricultural economic opportunities for developing nations," said Mellinger. "Malaysia provides an excellent example of how this has succeeded. There, public health issues have been proactively addressed, which is reducing the impact of disease on the population. Additionally, fewer resources are spent producing crop commodities in favor of developing service and manufacturing industries."

"Unfortunately, Malaysia's coastal and ecological advantage isn't shared by much of sub-Saharan Africa, where geographical conditions are more intractable. Combating poverty there will require serious redoubling of global aid efforts to address the unique conditions facing those populations," Mellinger said.