Regional wealth can depend on Jack Frost. According to researchers, cold weather bolsters agriculture, the underpinning of a wealthy society.

In winter months, when you first step out the door in the morning to greet a blast of bone-numbing cold air, remember to be thankful. According to research from Purdue and Tufts Universities, cold weather has something to do with our relative prosperity.

Still, if periods of cold weather are linked to prosperity, you may be wondering why real-estate prices in Miami Beach bear somewhat of a premium to, say, Fargo.

The answer comes from the realms of economics, a field where it is essential to remember an important disclaimer--everything is relative. What is fascinating is that the answer rallies around a society's agricultural prowess: Periods of cold weather tend to make for more fertile soils; cold weather breaks the disease cycle and provides a natural control against insects.

Economists William Masters of Purdue University and Margaret McMillan of Tufts University used new advances in global information systems data to compile information for a recently published paper, "Climate and Scale in Economic Growth."

They wanted to answer that age-old question of why societies in temperate regions may have advanced more than tropical regions.

Since antiquity, observers have noted differences between people living in the tropics and those living in temperate zones. In 350 B.C., the Greek philosopher Aristotle wrote, "Those who live in a cold climate are full of spirit."

And from at least the time of Adam Smith's 1776 "Wealth of Nations" to 1998's Pulitzer Prize-winning book by Jared Diamond, "Guns, Germs, and Steel," people have speculated why some areas of the globe are wealthy while others seem destined for poverty.

"The broad puzzle is why are poor countries in geographic tropics, and most of the wealthy countries are not in the tropics," Masters said.

"For the first time, we can put detailed biophysical data into economic models to try to understand how climate and geography have influenced economic performance without indulging in economic determinism," Masters said. "Learning about the causes of persistent poverty helps us see what can be done about it."

They discovered that the factors differentiating wealthy countries from poor included annual hard frosts. McMillan said this finding was unexpected. "A generation of economists have focused on institutions as the key differences between societies," she said. "Many of them--including me--are now quite surprised to find that biophysical factors like climate matter, too."

Cold weather has two major effects, the researchers say: The temperate areas have historically had less disease and better agriculture, at least from the point where the citizens of those countries learned how to take advantage of the seasonal frost cycle.

"Having frost and winter forces insects into a dormant state, which makes it much easier to control insect-borne diseases. In the United States we had malaria, and we had other diseases, but we were able to more easily eradicate these than in other countries, partly because the insects are knocked back [by winter] each year," said Masters.

The connection between frost and agricultural success isn't always as obvious. "People think of the frost-free tropics as a lush paradise with abundant biodiversity, and there are abundant species in the tropics," Masters said. "But too much biodiversity can be a big problem. We get annual crops out of the tropics and plant them in the temperate regions and they do better. Corn, potatoes, wheat and virtually all of our crop species first evolved in the warmer areas of the world but are now grown for export by countries in temperate regions."

Part of the reason for this is that frost allows a build-up of organic matter that leads to rich, fertile topsoil.

"In the tropics, that matter is broken down by insects and microbes very quickly, and the nitrogen and carbon in the dead-plant material evaporate into the air or are leached into the ground by rainwater," Masters said. "In a temperate zone, that nitrogen and carbon build up and remain in the soil in the form of organic matter."

Another benefit of frost is that it ensures moist soil for spring planting. Snow and ice accumulate in the soil through the winter and then are released as water in the spring. Farmers in temperate areas, unlike those in tropical regions, rarely have to worry about seasonal rains.

Although the economies of many of the wealthiest nations are no longer based on agriculture, the researchers say past success in agriculture has an historical echo effect that allowed these nations to accumulate and build capital.

"Looking forward," the researchers write in the paper, "tropical countries could be helped to grow not only through trade, but also through technical change from accelerated investment in public health and agricultural research."

Helping tropical nations catch up will require more than scientific advances, though, Masters said.

"The kinds of technologies involved, such as vaccines for tropical diseases and crop varieties adapted to tropical conditions, could be developed if we were willing to pursue them. But most tropical regions are too poor to attract enough research and development from private pharmaceutical and agribusiness firms," he said. "So public-sector investments are needed, and that depends not on science, but on the calculus of politics."