A global economy alters the impact of changes in the environment. The question addressed by this project is when the economy became truly "global." The answer is to be found in the statistics of prices in different countries, which converge as the market becomes wider in extent. Detailed studies of particular gaps in prices--such as the 570 percent gap between the price of wheat in Poland and in Northern Italy during the 15th century--test how much the convergence resulted from falls in transport costs and how much from institutional changes, such as peace, literacy, and security of contract. The statistical material is supplemented with linguistic and cultural information. The methods employed are used in economics and geography, but have not been applied to the longer-term history of the market. The objective is to measure price convergence over many centuries, from ancient times to the present, in order to give a standard for "the" market. Such a standard forms the background for scientific studies in economics, human ecology, geography, and history. The connection between environment and the economy is not as simple as it looks from the biological perspective. The economy amplifies or dampens the impact of the physical environment. To project the complex of environmental and economic change into the future is difficult at best, sensitive to errors of specification in the mode: the best work of economists and meteorologists and ecologists agree that twenty years out we are guessing crudely. But we can know the past. From documentation of forecasted areas we can know how rapidly Icelandic topsoil has been eroded by cultivation int he millennium of settlement. From new isotope techniques we can know the long and startlingly stable history of carbon dioxide in the atmosphere. Global warming and chilling have happened before in recorded history, chronicles for example in the growth rings of the bristlecone pine. Contrary to recent fears, global warming has on the whole been good for humans, and in particular has expanded the market and the high culture that goes with the market. The unusually warm decades or centuries around 1500 BC, the birth of Christ, and 1200 AD saw the market expand and civilization flourish. The unusually cold decades or centuries around 1000 BC, 700 AD, and 1350 AD were notorious setbacks to markets and culture. The global market and the global ecology are connected, but in ways both benign and malignant, and in any case not easily predicted.
