Since Hurricane Katrina hit the Gulf Coast three years ago, we've reported extensively on the factors that contributed to making the storm one of the worst disasters ever to afflict the United States. One of the themes that's come up time and again is land loss -- the disappearance of the region's critical coastal wetlands into the Gulf of Mexico.

For decades, Louisiana has been losing up to 40 square miles of wetlands each year, an amount that represents about 80 percent of the entire nation's annual coastal wetlands loss. If nothing is done to slow the current rate of coastal erosion, an additional 800,000 acres of Louisiana wetlands will vanish into the sea by the year 2040, and the state's shoreline will move inland as much as 33 miles in some places. Because coastal wetlands play an important role in absorbing the impact of approaching storms before they hit populous areas, their disappearance will continue to intensify hurricanes' impact on the region.

Coastal erosion is also having a devastating effect on communities and cultures across the Gulf, as spotlighted in today's New York Times story about the impact of land loss on Louisiana's historic Cajun shrimping communities.

The Times report attributes Louisiana's land loss solely to the building of the levee system. And it's certainly true that levees have worsened wetlands losses by preventing the routine deposit of land-building sediments. But there are other critical factors exacerbating Louisiana's land loss that the Times fails to mention.

Like offshore drilling for oil and gas.

Offshore drilling operations carve out channels in coastal wetlands for exploration as well as for transporting resources back to the mainland. Those channels in turn provide a route for Gulf waters to wash inland, the salinity eventually killing trees and other plants that help stabilize land, further exacerbating its erosion.

To date, oil and gas companies have dug an estimated 10,000 miles of canals across the state's wetlands. Since 1983, Shell Oil alone has dredged about 22,000 acres of Louisiana wetlands for placement or maintenance of pipeline canals and other production facilities. Environmental advocates recently tried to present the company with a bill for $362 million for the damage.

At the same time offshore oil and gas operations are eroding coastal wetlands, ocean levels are rising due to global climate disruption, while a warmer atmosphere is intensifying tropical storms and hurricanes. The situation has resulted in an ongoing disaster for Louisiana.

The current bipartisan push to expand offshore drilling along the Southeast coast risks bringing to other states the same problems Louisiana is grappling with. One of the hard-learned lessons of Katrina is that we ignore offshore drilling's destructive impact on our fragile coastal wetlands at our peril.

(Photo from the U.S. National Oceanic and Atmospheric Administration)