For years, climatologists have observed that smog, soot and smoke are contributing to a phenomenon dubbed global dimming. Climate statistics show that a significant amount of sunlight is literally being blocked from reaching the Earth's surface by emissions from smokestacks, diesel engines and forest fires.

Recent climate data, however, now show that the air is clearer than a decade ago and that more sunlight is reaching the Earth. Apparently pollution control measures are working. Great news! Or is it? Though there's less particulate matter in the air, fossil fuels continue to be burned at a furious pace, and carbon dioxide "greenhouse" gas continues to increase and trap heat in the atmosphere. Now scientists are concerned that adding more sunshine to the greenhouse effect will exacerbate the speed of global warming.

One hope is that crops, trees and vegetation will be able to photosynthesize more efficiently with more sun, converting carbon dioxide into oxygen and sequestering carbon in the soil. At some point in the future, the government might even pay farmers to farm in a way that maximizes carbon sequestration. Currently 30 laboratories across the country participate in the GRACEnet project — Greenhouse Gas Reduction through Agricultural Carbon Enhancement network. The project monitors greenhouse gas emissions (carbon dioxide, nitrous oxide and methane) from cropland and pasture, with the goal of reducing these emissions.

Many scientists believe that even a small increase in the amount of carbon stored per acre of farmland would have a large effect on offsetting U.S. greenhouse gas emissions. They say farms and ranches have the potential to store enough carbon to offset 8 to 10% of total U.S. emissions. Decreasing nitrous oxide and methane emissions would be an additional benefit that agriculture could provide.

To learn more, visit the following Web sites:

Global "brightening"
http://www.nature.com/news/2005/050502/full/050502-8.html

Carbon sequestration in crops
http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=169412=1

Developing a carbon sequestration policy
http://sciencepolicy.colorado.edu/carboncycle/workshop/supply_demand_ccs_agriculture_RC.pdf