Rising sea or sinking land?

Rising sea level is a perennial bone of contention among climate-change alarmists. In a recent interview, TV personality Bill Nye “the science guy” stated “the first climate-change refugees” were being rescued from a sinking village in a Louisiana bayou.

Rising sea level, allegedly driven by man-made global warming, is often theorized by warmists as the culprit causing shore-line erosion worldwide. But natural processes, not a hypothesized CO2-driven sea rise, play the dominant role.

The Biloxi-Choctaw villagers on Isle de Jean Charles, La., are not unique in their predicament, being subject to frequent flooding. Adversity faces some residents living on coral atolls in the Solomon Islands and Tuvalu both in the South Pacific and on certain Maldives islands in the Indian Ocean.

For centuries Venice, Italy, has contended with waters from the Adriatic, rising into its iconic canals. Actually the land under the city is slowly sinking by a natural process referred to as “subsidence.” The sheer weight of the ancient city forces out water from underlying sediments and the compaction results in subsidence. Coastal areas where sea water encroaches onto adjoining land, are more properly described, not as examples of “sea level rise” (SLR) but as “relative sea level rise” (RSLR), as measured by tide gauges. As land sinks, the ocean appears to rise.

Subsidence is the principal cause for flooding and shoreline erosion at the mentioned locations and other places as well. The open ocean continues to rise at only 6-7 inches per century averaged on a millennial scale.

An article in National Geographic describes how Pacific coral atolls are shaped by storms. Surprisingly, most are not losing their land area. Corals grow fast enough to keep pace with RSLR as they deposit new shell material, maintaining an optimal level for the growing reef. Then as major storms inflict physical damage to the structure, broken coral fragments are gathered by wave action to anchor new land along the lee of the atoll. Commonly more material is added to the atoll than is lost to deeper surrounding water.

It’s not uncommon for low-lying islands like coral atolls to form, disappear (partially or completely), then re-form as corals adapt to change. Australia’s Great Barrier Reef has existed for millions of years and survived numerous assaults, including rise and fall of sea level on at least four occasions during the past million years. Nature is indeed resilient.

But what of the fate of humans living on land a few feet above high tide? What can be done?

An option is to resettle at-risk communities to higher ground as is being done for the Biloxi-Choctaw. Their houses perch precariously along a narrow ridge being eaten away by subsidence-driven shoreline erosion and swamped during spring tides, leaving them vulnerable to the next large storm.

All of southern Louisiana formed concurrently with the melting of the last continental glaciers when sea levels rose dramatically. The Mississippi River hauled vast quantities of sediments gathered from out-wash of melting ice to the north. The lower reaches of the Great River became a choked, braided stream forming several delta lobes into the Gulf of Mexico in succession. Distributaries dumped suspended glacial debris producing a complex pattern of shorelines consisting of low-lying islands separated by a skein of bayous, marshes, and lakes. As long as fresh alluvium was being delivered by a functioning distributary, the islands grew in area and elevation.

Throughout the past century levees and stabilized channel systems were constructed along the Mississippi to provide navigable waterways and prevent seasonal flooding. Federal policy resulted in major amounts of sediment being transported into the Gulf of Mexico proper—and no longer distributed within bayou country.

The arrangement led to some deleterious effects: 1) The sediments deposited into deep Gulf waters produced anoxic (dead) zones along the bottom, and 2) Bayous were deprived of alluvium needed to restore land lost (inevitably) to coastal erosion driven by subsidence. In effect the bayou country was being starved of materials it needed to maintain itself as it had done for previous millennia.

The Corps of Engineers’ technical successes guaranteed land would be lost from bayous, no longer supported by deposition of fresh alluvial sediments during floods. The outcome was predetermined and it cannot be reversed by ineffectual measures promoted by the states’ attorneys general and Bill Nye to reshape the course of future climate.

William D. Balgord, Ph.D. (geochemistry), heads Environmental & Resources Technology, Inc. in Middleton, Wisc.Thinking of submitting an op-ed to the Washington Examiner? Be sure to read our guidelines on submissions.