Research & Commentary: Land Subsidence, Not Climate Change, Is the Cause of Water Intrusion in and Around Chesapeake Bay

Published November 6, 2017

A report released in October 2017 by the Nongovernmental International Panel on Climate Change (NIPCC), titled “Will Global Warming Overflow Chesapeake Bay?“, says the available research indicates water intrusion problems in the area around the Chesapeake Bay are not due to sea-level rise induced by anthropogenic (man-caused) global warming, “but primarily to land subsidence due to groundwater depletion and, to a lesser extent, subsidence from glacial isostatic adjustment.”

“Land subsidence” is the sinking or lowering of the land surface, mostly due to human activity. It can “increase flooding, alter wetland and coastal ecosystems, and damage infrastructure and historical sites,” as well as “contribute to water intrusion and shoreline retreat.”

Study author Roger H. Bezdek notes that analyses have found up to 176,000 residents living on the shores of the Chesapeake could be “either permanently inundated or regularly flooded by [the year] 2100,” with up to $26 billion in damage to personal property and the inundation of 120,000 acres of “ecologically valuable” land. Land subsidence might also affect more inland areas of the watershed, such as the Blackwater River Basin in Virginia, which could possibly be subject to increased flooding.

According to Bezdek, groundwater withdrawals are responsible for roughly 80 percent of the land subsidence in the United States. In the Chesapeake region, these groundwater withdrawals are leading to “aquifer-system compaction.”

“When groundwater is pumped from an aquifer system, water pressure in the system decreases. The pressure change is reflected by water levels in wells, with water levels falling as aquifer-system pressure decreases,” Bezdek notes. “This is happening over most of the Chesapeake Bay region, with the greatest drops in water-level seen near the pumping centers of Franklin and West Point, Virginia. As water levels fall, the aquifer system compacts, causing the land surface above to subside. Water levels have fallen over the entire Virginia Coastal Plain in the Potomac aquifer, which is the deepest and thickest aquifer in the southern Chesapeake Bay region and supplies about 75 percent of groundwater withdrawn from the Virginia Coastal Plain aquifer system.”

Bezdek also points out bedrock in the mid-Atlantic states is slowly moving downward in response to the melting of the Laurentide ice sheet, which covered a large chunk of North America during the most recent ice age. “When the ice sheet still existed, the weight of the ice pushed the underlying Earth’s crust downward and, in response, areas away from the ice sheet were forced upward (called glacial forebulge),” Bezdek wrote. “The southern Chesapeake Bay region is in the glacial forebulge area and was forced upward by the Laurentide ice sheet. … As the ice melted and its weight was removed, glacial forebulge areas, which previously had been forced upward, began sinking and continue to sink. This movement of Earth’s crust in response to ice loading or melting is called glacial isostatic adjustment.”

The study claims data indicate this land subsidence is responsible for most of the sea-level rise measured in the Chesapeake over the past 50 years. Therefore, “water intrusion may thus continue even if global sea levels do not rise or even decline. This finding suggests policymakers in the Chesapeake Bay area—in Maryland and Virginia in particular—should look to changes in local land and water use rather than concern themselves with global warming.”

One of these changes policymakers could address would be the reduction of aquifer-system compaction, which the study shows is the primary cause of land subsidence in the Chesapeake. Bezdek notes resource managers in the Houston-Galveston area of Texas and the Santa Clara Valley in Northern California “have successfully decreased land subsidence by moving groundwater pumping away from the coast, reducing groundwater withdrawal rates, and increasing aquifer recharge.” These results have been mirrored in California’s San Joaquin Valley, coastal Louisiana, China’s Yellow River Delta, and the Ganges-Brahmaputra Delta in Bangladesh.

“Water intrusion problems in the Chesapeake Bay—or elsewhere—cannot be successfully resolved unless their causes are correctly identified and appropriate remedies devised,” Bezdek concluded. Climate change is a red herring, and focusing on it will not resolve the Chesapeake’s land subsidence problem.

The following documents provide more information on land subsidence, sea-level rise, and climate change:

Will Global Warming Overflow the Chesapeake Bay?
This NIPCC Policy Brief finds flooding problems in the Chesapeake Bay region – Maryland and Virginia, in particular – are due not to sea-level rise, but to land subsidence. Author Roger H. Bezdek explains land subsidence and relative sea-level rise; discusses the causes of land subsidence in the Chesapeake Bay region; and points out the links between groundwater withdrawals and land subsidence.

Data versus Hype: How Ten Cities Show Sea Level Rise Is a False Crisis
Dennis E. Hedke, a geophysicist and past president of the Geophysical Society of Kansas and the Kansas Geological Society, reports and analyzes real data collected from 10 coastal cities with long and reliable sea-level records in this NIPCC Policy Brief. Those cities are Ceuta, Spain; Honolulu, Hawaii; Atlantic City, New Jersey; Sitka, Alaska; Port Isabel, Texas; St. Petersburg, Florida; Fernandina Beach, Florida; Mumbai/Bombay, India; Sydney, Australia; and Slipshavn, Denmark. He concludes the fear of rising sea levels is not a justification for reducing carbon-dioxide emissions or adopting policies that would have that effect.

10,000 To 5,000 Years Ago, Global Sea Levels Were 3 Meters Higher, Temperatures 4–6° C Warmer
Climate alarmists persistently claim human-caused climate change is causing sea levels to rise to an unnatural degree. In response, No Tricks Zone has compiled a list of studies examining sea levels from around the world. Those studies show sea levels have varied radically since the end of the most recent ice age, often being several feet higher than at present. Studies show historic sea levels at locations around the globe have been much higher in recent history than now.

Why Scientists Disagree About Global Warming
In this book published by The Heartland Institute, authors Craig Idso, Robert M. Carter, and S. Fred Singer say the most important fact about climate science, which they say is often overlooked, is scientists disagree about the environmental impacts of the combustion of fossil fuels on the global climate. There is no survey or study showing “consensus” on the most important scientific issues, despite frequent claims by advocates to the contrary. Scientists disagree about the causes and consequences of climate for several reasons. The authors say the only “consensus” among climate scientists is human activities can have an effect on local climate and the sum of such local effects could hypothetically rise to the level of an observable global signal. The key questions to be answered, they say, are whether the human global signal is large enough to be measured, and if it is, does it represent or is likely to become a dangerous change outside the range of natural variability? On these questions, an energetic scientific debate is taking place on the pages of peer-reviewed science journals, say the authors.

Climate Change Reconsidered II: Physical Science
Climate Change Reconsidered II: Physical Science is an independent, comprehensive, and authoritative report on the current state of climate science, published in October 2013. It is the fourth in a series of scholarly reports produced by the Nongovernmental International Panel on Climate Change, an international network of climate scientists sponsored by three nonprofit organizations: the Center for the Study of Carbon Dioxide and Global Change, the Science and Environmental Policy Project, and The Heartland Institute. (Also see the executive summary of Climate Change Reconsidered II: Physical Science

Climate Change Reconsidered II: Biological Impacts
Released on April 9, 2014, Climate Change Reconsidered II: Biological Impacts is an independent, comprehensive, and authoritative report on the impacts of climate change on plants, terrestrial animals, aquatic life, and human well-being. (Also see the Climate Change Reconsidered II: Biological Impacts “Summary for Policymakers”:


Nothing in this Research & Commentary is intended to influence the passage of legislation, and it does not necessarily represent the views of The Heartland Institute. For further information on this subject, visit Environment & Climate News, The Heartland Institute’s website, and PolicyBot, Heartland’s free online research database.

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