EXPECTED AND UNEXPECTED FINDINGS
Results for the impacts of climate change and rising carbon dioxide concentrations (assuming business as usual, with no emissions restrictions) brought few surprises. For example, the estimated carbon dioxide and temperature increases would benefit vegetation in much of the world.
The effects of ozone are decidedly different.
Without emissions restrictions, growing fuel combustion worldwide will push global average ozone up 50 percent by 2100. That increase will have a disproportionately large impact on vegetation because ozone concentrations in many locations will rise above the critical level where adverse effects are observed in plants and ecosystems.
Crops are hardest hit. Model predictions show that ozone levels tend to be highest in regions where crops are grown. In addition, crops are particularly sensitive to ozone, in part because they are fertilized. When crops are fertilized, their stomata open up, and they suck in more air. And the more air they suck in, the more ozone damage occurs, said Reilly. It's a little like going out and exercising really hard on a high-ozone day.
What is the net effect of the three environmental changes" Without emissions restrictions, yields from forests and pastures decline slightly or even increase because of the climate and carbon dioxide effects. But crop yields fall by nearly 40 percent worldwide.
However, those yield losses do not translate directly into economic losses. According to the economic model, the world adapts by allocating more land to crops. That adaptation, however, comes at a cost. The use of additional resources brings a global economic loss of 10-12 percent of the total value of crop production.
THE REGIONAL VIEW
|Contact: Elizabeth Thomson|
Massachusetts Institute of Technology