[GWSG] Climate Cart extract: Sea Level Rise

[Tilley, Al]

The Climate Cart
Issue 2: Sea Level Rise  (extract) July, 2023

The following is an extract adapted from the second issue of a series, Climate Cart, prepared for the Sierra Club’s Climate Adaptation and Restoration Team, on which I serve. The purpose of the series is to provide compact, up-to-date information on aspects of the climate crisis in which local action can make a difference.

We are experiencing accelerating sea level rise. We have had about 8” of rise in the last century, and are headed for a lot more.
Some of the rise will come from expansion of the oceans as the heat grows. In some places, the land is sinking, so sea levels will increase there; in others, it is rising. Even changing gravity as ice masses grow or shrink can contribute to local sea levels. More rise will come from our melting glaciers, from the Alps to the Himalayas to the Andes. Most of the rise, though, will come from melting polar ice sheets. For a very long time glacial and polar ice has been roughly in balance, with snowfall making up for yearly melting. That balance has been lost because the blanket of carbon around the earth from the burning of fossil fuels traps heat in the atmosphere which was once lost to space.

How much rise in our oceans we may expect depends partly on our success in controlling emissions of carbon dioxide, methane, and the other greenhouse gases. Some rise is inevitable from the heat imbalance we have already produced—and that grows daily as we burn coal, oil and gas. Studies indicate that the Greenland Ice Sheet and the West Antarctic Ice Sheet are destabilized. Greenland would raise seas 20 feet, and the West Antarctic, 14 feet. If we are so weak as to do nothing about it, that would come slowly, as humans measure time—centuries, some suggest. Recent findings about the West Antarctic, though, indicate that at least part of it, the Thwaites Glacier, has in the past fallen into the ocean over a period of only a few decades, and we should be ready for the prospect that we will get significant rises on a yearly basis. Totten Glacier and others in the East Antarctic are also unstable.

Greenland, too, may have surprises. The unexpected rate of melt of Greenland’s Petermann Glacier suggests that sea level rise estimates have been too low. According to a study in PNAS, the grounding line has been found to respond to tidal flows, allowing warm water to intrude. If other glaciers ending in the ocean are in similar patterns, sea level rise projections could increase by as much as 200%. https://phys.org/news/2023-05-rapid-ice-greenland.html
If we were to restore the climate by drawing down carbon from the atmosphere we could moderate and even reverse sea level rise. That is worth our effort to promote.

NOAA maintains a projection of sea level rise, regionally adjusted, which has become the standard for planning in the US. While the possibilities are described under a range of levels, so far we have experienced rises toward the high level of projection. It is prudent that we base planning on the NOAA high level figures. The primary sources of variation are the polar ice sheets, for we know too little about their rate of destabilization to make tight projections.
Sea level rise can destabilize our barrier islands. Many coastal communities are on such islands. Even without the wild cards at the poles, we expect a couple of feet of sea level rise around mid-century. Satellite estimates of ice loss from the Greenland and Antarctic ice sheets show acceleration—20% increase in yearly loss from Greenland 2010-20, a seven-fold increase since the 1990s. Acceleration in the Antarctic is slower—64% since the 1990s. Through this study and others “we have come to learn that ice responds rapidly to our changing climate." Sea level rise projections are likely to increase.  https://phys.org/news/2023-04-devastating-greenland-antarctic-ice-sheets.html

Some coastal communities have already done vulnerability studies to inform themselves about what is coming. All should undertake such a study, and we can urge our cities to undertake a thorough and complete vulnerability study. In her recent book Charleston: Race, Water, and the Coming Storm, Susan Crawford adds up the effects of the slowdown of the Atlantic Meridional Overturning Circulation, the destabilization of Thwaites Glacier in the West Antarctic, and the heating of the world’s oceans to project that Charleston should plan for “eight feet of sea level rise over decades, not centuries.” (Chapter Two, penultimate paragraph).

Most vulnerability studies do not take groundwater levels into account. They should. In coastal areas, groundwater levels rise higher than sea levels. That has been common knowledge in the scientific community since studies were done in Hawai’i about ten years ago. However, not much application of that knowledge has been included in sea level rise vulnerability studies. “A new report finds that over the next century, rising groundwater levels in the San Francisco Bay Area could impact twice as much land area as coastal flooding alone, putting more than 5,200 state- and federally managed contaminated sites at risk.” Obviously, other coastal regions need to do similar studies. https://news.berkeley.edu/2023/06/20/rising-groundwater-threatens-thousands-of-toxic-sites-in-the-bay-area/ The study in Hawai’i also found that flooding estimates doubled when groundwater levels are included. We in coastal areas can press authorities to pay attention to groundwater levels.

Obviously, we should not be developing new structures on a plain to be flooded soon. We should be preparing for current wetlands to become first marsh and then open water as they migrate inland, and we should be cleaning up brownfields, septic tanks, dumps, and the rotten gasoline under old gas stations before they have a chance to pollute the waters which will cover them. Coastal communities may face relocation. There is a great deal we can and should do even if local authorities are shy about looking at our situation squarely.

If you are in a coastal area, chances are that your community is already experiencing the effects of sea level rise and will support your efforts to spur vulnerability studies, planning, and action to anticipate the coming crisis.

The August 2023 of the Climate Cart will be on excessive heat. Our intention is to present an up-to-date discussion on the following topics: vulnerability studies; sea level rise; excessive heat; floods, drought and water supply; public health; relocation programs and community rebuilding; and rewilding. We believe that these are matters in which local action can make a difference. If you are not a member of an ecologically active group such as the Sierra Club you can still be a voice in your community for a livable future.

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