Merchandise trade currently accounts for only about 20 percent of global GDP, with agriculture representing just a small part of global trade. But even at these relatively low levels of trade, the transportation sector consumes nearly 60 percent of the world's oil and produces a quarter of all energy-related carbon-dioxide emissions. Oil use by transportation has almost doubled since 1973. Transportation-related emissions are growing at about 2.5 percent annually -- faster than any other sector in the economy.
Any dramatic increase in global trade could add substantially to the world's annual carbon-dioxide emissions. Particularly problematic is the growing use of trucks and airplanes at the expense of slower and more efficient trains and ships. Technological breakthroughs for freight transport are not yet on the horizon. Improvements in fuel efficiency are possible, but studies show that they would encourage more long-distance transport due to lower operating costs and are unlikely to prevent emissions growth in the face of increasing demand.
Given the general scientific consensus that carbon-dioxide emissions will have to drop below 1990 levels within a few decades in order to stabilize the climate at the lower end of various warming scenarios, long-distance trade poses a serious challenge. If the world's future economic development depends largely on global trade, then in the absence of radically new transportation technologies, we are likely to face the ultimate conflict between the economy and the environment. If global trade in agricultural products is the only way out of poverty for hundreds of millions of rural poor in developing countries, the conflict may well turn out to have an additional tragic dimension.