Sea Level Rise is Due to More than Climate Change

Within 50 years the Tangier Islands a complex of what are now several islands in the Virginia waters of the Chesapeake Bay will be mostly gone, consumed by the rising sea level in the region. Though the Intergovernmental Panel on Climate Change (IPCC) noted in its most recent report that sea levels have risen an average of 5 inches worldwide over the last 40 years, locally, the relative sea level has risen more closer to 7 inches over the same period.

The recently negotiated Paris agreement on climate change is not going to stop the loss of he the Tangier Islands. The agreement states that the goal is to limit global warming to less than 2 degrees Celsius above pre-industrial levels and try to limit it to 1.5 degrees Celsius. However, the voluntary nationally determined targets on limiting greenhouse gas emissions will not (according to the climate models) to come close to achieving that goal, and China and India did not agree to any reductions or limits to the growth of their carbon dioxide (CO2) emissions. The global emission of CO2 will continue to grow along with the emissions from those countries. How the nations treat the so called “ratchet mechanism” of the emissions reductions will ultimately determine the success or failure of the agreement in the long term, but not in the next century.

There is one other essential element of this picture we should discuss. Our understanding of climate and climate change is based on computer models and mathematical representations of the climate system. The model fundamentals are based on established physical laws and observations of the planet combined with extensive simulations of the atmosphere, ocean, cryosphere and land surface of earth. Nevertheless, models still show significant errors. Although the errors are generally greater at smaller scales, important large-scale problems also remain. For example, deficiencies remain in the simulation of tropical precipitation, variation in tropical winds and rainfall and sea level rise. Scientists believe that the ultimate source of most such errors is that many important smaller-scale processes are not represented in the models, which are built mostly using larger-scale features of the climate and planet. Essentially, the planet is too complicated for us to completely understand and model accurately with current technology and understanding.

The most looming threat may be from rising sea levels and it’s not just a threat to the island states. Virginia is experiencing tidal erosion and rising sea levels (or sinking land) along the 5,000 miles of tidal shoreline in Virginia. Approximately 15,000 years ago the ocean coast was about 60 miles east of its present location, and sea level was about 300 feet lower. At that time there was no Chesapeake Bay. Instead there was a river that meandered out to sea.

from Nature

Sea level continues to rise in the Chesapeake Bay, it was estimated that the sea level has risen 7 inches since 1971 and it is estimated by the climate models that this rise will accelerate in the future, but even if it doesn’t accelerate, it will continue as it has been going on for over 15,000 years. Now a report by the Army Corp of Engineers published in the Journal Nature on December 10, 2015 has predicted that the Tangier Islands in the Virginia waters of the Chesapeake Bay will likely have to be abandoned within 50 years. These islands lie within a hot spot of relative sea level rise that is significantly higher than the mean seal level rise on earth. The complex of several islands were once connected and have been disappearing in my lifetime. The main remaining Islands are Goose, Uppards, Port Isobel and Tangier Island. Only Tangier is still occupied.

The sea level rise hot spot extends from Cape Hatteras, North Carolina to Boston, Massachusetts, but the Southern Chesapeake Bay region within the hot spot has had a higher rate of sea level rise due to land subsidence. Land subsidence due to glacial rebound after the Laurentide ice sheet melted, excessive groundwater extraction, as well as the effects of the meteor impact near Cape Charles, Virginia (about 35.5 million years ago) are all causing the effective sea level rise to be about an inch ever 25 years. Aquifer-system compaction from groundwater being pumped accounts for more than 50% of the land subsidence observed in the coastal region. 

The Army Corp of Engineers report that the Tangier Islands have lost the majority of their land mass since the islands were first mapped in 1850 due to a combination of wave-induced erosion and sea level rise. They predict that the Islands will lose the majority of their remaining landmass in less than 50 years. Though there are actions that can be taken to forestall the fate of the Islands, the fate of the Island seems sealed and will be blamed on climate change thought it is due in almost an equal parts to groundwater extraction. It is essential that we not loose sight of the importance of sustainable groundwater and surface water use in trying to save the planet by reducing CO2 emissions.