John’s Blog/Newsletter: SEA LEVEL RISE NOW

There was considerable news last Friday about the latest US Government report on the Impacts of Climate Change, a legally required document every 4 years. The “Fourth National Climate Assessment, Volume 2, The Impacts” (sometimes referred to as NCA4) is well grounded in science, yet is quite clear and generally avoids technical language. It is an excellent piece of work, that builds upon and affirms what the science community has been saying with increasing clarity and alarm.

13 Federal Agencies contributed to the report and approved its content: the departments of Agriculture, Commerce (including NOAA and National Weather Service), Defense, Energy, Health & Human Services, Interior, State, Transportation, plus the EPA (Environmental Protection), NASA, the National Science Foundation, The Smithsonian, and USAID (Agency for International Development).

It is sobering in its description of the effects of a warming planet that can now be seen clearly, manifesting as changing weather patterns, worse wildfires, agricultural disasters, and worse flooding–as well as drought. Key effects on the United States are:

• $ 1 Trillion dollars of US Real Estate is at risk from flooding due to rising seas, king tides, storms, record rainfall, and runoff. Almost fifty million U.S. residences are at risk (49.4 to use their exact figure).
• More than 60,000 miles of U.S. roads and bridges in coastal floodplains are now vulnerable to extreme storms and hurricanes that cost billions in repairs.
• As much as 10% of the US Gross Domestic Product will be eliminated by flooding, fires, agricultural impacts, and human health effects.
• A substantial rise in levels of atmospheric pollutants like ozone and smoke, which can cause respiratory problems and lead to premature death.

There was so much good press coverage that I will avoid a detailed review of the overall report. To quickly recap, based on extensive research they affirm and raise the alarm on these key points.

• The world is warmer and getting more so. Some of the worst effects are on agriculture, fresh water supplies, and the melting Arctic.
• Weather patterns are changing with complex effects from severe storms to record rainfall as well as drought.
• New outbreaks of disease, and ecological impacts from an explosion in tick-borne Lyme disease to the pine forest killer beetle are all associated with the warming temperature.
• The problem correlates with the elevated level of carbon dioxide in the atmosphere, which must be tackled with extreme urgency to avoid catastrophe.
• It is not too late to stave off the worst scenarios, but every year of delay makes it harder to stabilize.

What does it say about rising sea level?

Given my focus on about sea level rise, I want to help pull that content out of the perhaps overwhelming scope of the NCA4. Following  are some select passages, along with my comments / interpretation.

America’s trillion-dollar coastal property market and public infrastructure are threatened by the ongoing increase in the frequency, depth, and extent of tidal flooding due to sea level rise, with cascading impacts to the larger economy. Higher storm surges due to sea level rise and the increased probability of heavy precipitation events exacerbate the risk.

COMMENT:  Many coastal communities will be transformed this century and will suffer financial impacts as chronic high tide flooding leads to higher costs and lower property values. Actions ahead of time to plan for and adapt to more frequent, widespread, and severe coastal flooding would decrease direct losses and cascading economic impacts.

Over the first half of this century, the future scenario the world follows has little effect on projected sea level rise due to the inertia in the climate system.

COMMENT: There is little we can do now to change the rate of SLR by mid century, due to the incredible amount of heat already stored in the sea.

However, the magnitude of human-caused emissions this century significantly affects projections for the second half of the century and beyond. Relative to the year 2000, global average sea level is very likely to rise by 0.3–0.6 feet (9–18 cm) by 2030, 0.5–1.2 feet (15–38 cm) by 2050, and 1–4 feet (30–130 cm) by 2100…. These ranges do not, however, capture the full range of physically plausible global average sea level rise over the 21st century. Several avenues of research, including emerging science on physical feedbacks in the Antarctic ice sheet, suggest that global average sea level rise exceeding 8 feet (2.5 m) by 2100 is physically plausible, although its probability cannot currently be assessed.

COMMENT: What we do in the next few decades to aggressively reduce CO2 emissions can have a big impact to slow and limit sea level rise in the latter part of the century. There is a delay in terms of the effect. We cannot put a numerical probability on the rise of more than 8 feet of SLR, due to the impossibility of predicting the exact collapse rate of Antarctica. But not being able to determine a number does not mean it is trivial. (As an analogy, if there was a known risk of an avalanche, we would not set our tents in the potential path, regardless of the uncertain probability.)

Regardless of future scenario, it is extremely likely that global average sea level will continue to rise beyond 2100. [Ancient] sea level records suggest that 1.8°F (1°C) of warming [which has already happened] may already represent a long-term commitment to more than 20 feet (6 meters) of global average sea level rise;  Under 3.6°F (2°C), [the goal of the 2015 Paris Climate Accords] about one-third of the Antarctic ice sheet and three-fifths of the Greenland ice sheet would ultimately be lost. [That equates to approximately 75 feet of sea level rise (20 meters).

COMMENT: Sea level will not stop rising for at least a century. What we do in the coming few decades can determine if we eventually get 20 feet of sea level rise, or several times that amount. Even with the extraordinary heat we are adding to the system, it takes a VERY long time to melt ice sheets the size of North America (the area of Antarctica and Greenland combined ) and miles thick.

I believe that there are two key conclusions from this:

1. We must slow the warming ASAP.
2. We must begin adapting in anticipation of higher sea level while there is time. The uncertain rate of rise is not an excuse to delay.

For those wanting to read the actual NCA4 report, with graphics, go to: Fourth National Climate Assessment, https://nca2018.globalchange.gov/ The report is quite readable and not too technical.