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Brief: Tipping Initiation, Restoration Reverses Some Sea Level Rise, Beach Disintegration, Limit to Sea Level Rise Adaptation

Brief Report: Climate Tipping, Earth Systems Collapse Initiation, Climate Restoration Reverses Some Sea Level Rise, and the Barrier Island Disintegration Threshold, Limit to Sea Level Rise Adaptation

A brief discussion with summarized academic findings.

Climate Tipping, Earth Systems Collapse Initiation

Greenland and Antarctica have seen their tipping activated. This does not mean they have passed the point of no return where collapse becomes irreversible. Hansen 2008 defines the point of no return as that point where even if the perturbation to the systems that caused the collapse to begin is removed, the system continues to collapses. This point of no return of Greenland and Antarctica is most likely still decades or generations in the future. Tipping is activated when equilibrium conditions are perturbed, which is what we have seen with half of known discrete tipping systems (Lenton 2019, McKay 2022), 20 physical and 21 biological systems (Ripple 2023), and 7 of 8 broad tipping systems (Rockstrom 2023). Feldmann and Levermann 2015 describe modelling that shows that if the perturbation to the West Antarctic Ice Sheet system that moved the systems out of equilibrium is removed before “the point of no return,” the systems will self-restore. Their modeling shows mid-century is the point of no return for the West Antarctic Ice sheet, with likely connections to the East Antarctic Ice Sheet at some point.

Climate Restoration Reverses Some Sea Level Rise

Climate restoration will actually allow sea level to recede a bit because of shrinking water with restoration cooling from today. Climate restoration will not restore ice sheets in time frames that matter, or restore all of the sea level rise caused by humans, but it will likely restore most of the sea level rise from ocean water expansion, which is about half of sea level rise we have experienced.  This lowering of sea level will proceed at the same speed as cooling the oceans (Boucher 2012), which can be faster than the speed at which we warmed them because of two feedbacks: heat burial and evaporative cooling. Melt that has already occurred will take generations or more like centuries and millennia to restore. But climate restoration will allow a new equilibrium to be established when we cool Earth back to within the evolutionary boundaries of the ice sheets.

Barrier Island Disintegration Threshold

Barrier island disintegration (destabilization) begins (it’s a system collapse) with sea level rise of 5 to 7 mm per year (Climate Change Science Program 2009). Disintegration though is largely controlled by storm surge events and barrier island geometry. Smaller barrier islands with less topography will succumb faster than 2 feet of rise, especially with storm surge implications. Larger islands like most of Padre Island will be slower than 2 feet of rise, unless we get a really big storm that blows the island apart. Then the rise rate of greater than 5 to 7 mm per year will disallow self-restoration.

Sea Level Rise Adaptation Limit

The critical piece of sea level rise science from IPCC AR5 is that 3 feet of sea level rise per century will limit adaptation strategies (IPCC 2014). When adaptation is limited, abandonment results with global economic implications. The Union of Concerned Scientists say that 9 inches of sea level rise by 2030 will create chronic nuisance flooding that initiates abandonment. NOAA 2017 says their intermediate-high scenario is 14 inches of sea level rise by 2030 (NOAA 2017).



Hansen 2008 – 350 ppm CO2… This is the most important work from Hansen that justifies returning our climate back to within the evolutionary boundaries of our current Earth systems.
Hansen et al., Target Atmospheric CO2 Where Should Humanity Aim?, Open Atmospheric Science Journal, November 2008.

Lenton 2019 – More than half of known tipping points are now active up to 100 years ahead of projections…  Nine Earth systems collapses have been identified by scientists as active: Arctic sea ice, Greenland ice sheet, boreal forests, permafrost, the Gulf Stream, the Amazon, coral, the West Antarctic Ice Sheet and parts of the East Antarctic Ice Sheet. Until 2018, the Intergovernmental Panel on Climate Change (IPCC) has assumed that tipping would not occur before 5 C of warming above preindustrial times, something that the worst-case scenario put well into the 22nd century. In 2018 however, IPCC lowered this limit to between 1 and 2 C above preindustrial times in both the 1.5 C Report and the Cryosphere Report.  Lenton tells us, “The Intergovernmental Panel on Climate Change (IPCC) introduced the idea of tipping points two decades ago. At that time, these ‘large-scale discontinuities’ in the climate system were considered likely only if global warming exceeded 5 °C above pre-industrial levels. Information summarized in the two most recent IPCC Special Reports (published in 2018 and in September this year) suggests that tipping points could be exceeded even between 1 and 2 °C of warming.”  Climate tipping is now active greater than 100 years ahead of projections.
Lenton et al., Climate tipping points-too risky to bet against, Nature, November 27, 2019.
University of Exeter Press –

McKay 2022 – Exceeding 1.5 C global warming could trigger multiple climate tipping points with self-perpetuating change… (Note: some  of these tipping points have already been identified as being crossed by others: Permafrost, the Amazon, West Antarctic ice Sheet, Greenland Ice Sheet, and the Gulf Stream.) “We show that even the Paris Agreement goal of limiting warming to well below 2°C and preferably 1.5°C is not safe as 1.5°C and above risks crossing multiple tipping points. Crossing these CTPs can generate positive feedbacks that increase the likelihood of crossing other CTPs. Currently the world is heading toward ~2 to 3°C of global warming; at best, if all net zero pledges and nationally determined contributions are implemented it could reach just below 2°C. This would lower tipping point risks somewhat but would still be dangerous as it could trigger multiple climate tipping points.” Tipping likely with a threshold of 1.5 C to less than 2 C: Greenland Ice Sheet, West Antarctic ice Sheet, Labrador Sea/Subpolar Gyre, low-latitude corals, Barents Sea ice, widespread permafrost thaw. At 2 to 4C: Amazon Rainforest dieback, East Antarctic Ice Sheet, Sahel/West African Monsoon, Mountain Glaciers. At +4 C: Atlantic Meridonal Overturning (Gulf Stream) Boreal Forest, Arctic Winter Sea Ice.”
“Self-perpetuation mechanisms are critical to the existence of a tipping point in a system, beyond which they propel qualitative change such that even if forcing of the system ceases the qualitative change usually continues to unfold regardless.”
McKay, Lenton et al., Exceeding 1.5 C global warming could trigger multiple climate tipping points, Science, September 9, 2022.
Press Release  – University of Exeter

Scientific reticence by journal editor with McKay 2022… – changes highlighted green.
Prepub says – “Climate tipping points occur when change in a part of the climate system becomes self-perpetuating beyond a forcing threshold, leading to abrupt and/or irreversible impacts.”
Final says – “Climate tipping points occur when change in a part of the climate system becomes self-perpetuating beyond a warming threshold, leading to substantial Earth system impacts.”

Ripple 2023 – 20 physical and 21 biological tipping feedback loops threatened… “Many feedback loops significantly increase warming due to greenhouse gas emissions. However, not all of these feedbacks are fully accounted for in climate models. Thus, associated mitigation pathways could fail to sufficiently limit temperatures. A targeted expansion of research and an accelerated reduction of emissions are needed to minimize risks…  We suggest that further small increases in short-term warming are a big risk, considering the suffering that we are already experiencing from climate disasters of ‘‘unprecedented’’
wildfires, intense storms, coastal flooding, permafrost thaw, and extreme  weather that have occurred with just 1.1C to 1.2C global average warming. Second, as part of a longer timeline, positive feedback loops and tipping points may pose a major threat. Given the potential for catastrophic climate
change and the lack of complete scientific understanding to date, policymakers should strongly consider the potentially dangerous effects of feedback loops, tipping points, and climate cascades, even if all desired scientific data are not available at this time… if the worst-case risks posed by feedback
loops and tipping points have been underestimated, the future of a hospitable planet Earth may be at stake.”
Ripple et al., Many risky feedback loops amplify the need for climate action, One Earth, February 17, 2023.
(Paywall),fail%20to%20sufficiently%20limit%20temperatures. Summary –

Rockstrom 2023 – Safe and just Earth systems boundaries identified where seven of eight quantified boundaries in over half of global land area are now exceeded… “We identify safe ESBs (Earth systems boundaries) for warming based on minimizing likelihoods of triggering climate tipping elements; maintaining biosphere and cryosphere functions; and accounting for Holocene (<0.5–1.0 °C) and previous interglacial (<1.5–2 °C) climate variability… Some climate tipping points, such as circulation collapse or Amazon dieback, have high uncertainty or low confidence in their dynamics and potential warming thresholds16, but the complementary palaeoclimate and biosphere analyses independently support the safe climate ESB assessment. Cryosphere function includes maintaining permafrost in the northern high latitudes, permanent polar  ice sheets and mountain glaciers and minimizing sea ice loss. We find that global warming beyond 1.0 °C above pre-industrial levels, which has already been exceeded9, carries a moderate likelihood of triggering tipping elements, such as the collapse of the Greenland ice sheet or localized abrupt thawing of the boreal permafrost16. One-degree Celsius global warming is consistent with the safe limit proposed in 1990 of 350 ppm CO2. Above 1.5 °C or 2.0 °C warming, the likelihood of triggering tipping points increases to high or very high, respectively (high confidence in Extended Data Table 1). Biosphere damage and the risk of global carbon sinks becoming carbon sources, potentially triggering further climate feedbacks, increase substantially.”
Seven ESB’s beyond their safe zone: Biosphere – natural ecosystem area, Biosphere – functional integrity, Water – surface flows, Water – groundwater flows,  Green water – soil moisture, Nutrient cycles – nitrogen, Nutrient cycles – phosphorus, Atmospheric loading – aerosols.
Rockstrom et al., Safe and just Earth system boundaries Nature, May 31, 2023.
Supplementary Materials – boundaries and discussion of climate tipping points begins on page 4.

Feldmann and Levermann 2015 – WAIS Collapse Initiation Reversal, Feldmann and LevermannPoint of No Return PONR … Advanced Antarctic Ice Sheet modeling shows the West Antarctic Ice Sheet has a collapse initiation period where collapse becomes irreversible. If the warming mid-ocean waters that are responsible for the collapse can be returned to normal temperatures by mid-century, the collapse initiation can be reversed. Otherwise, the collapse becomes irreversible after mid-century.
Feldmann and Levermann, Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin, PNAS, November 17, 2015.

Boucher 2012 – Ocean cooling, outgassing, re-emissions off gassing… Boucher 2012 says much of CO2 in the biosphere stays there for a very long time and there is a lag from emissions cessation to off gassing that is relative to ocean atmosphere equilibrium. The time to cool our oceans is roughly equal to the time it took to warm them, except if we cool faster than we warmed.
Boucher et al., Reversibility in an Earth System model in response to CO2 concentration changes, Environmental Research Letters, May 9, 2012.

US Climate Change Science Program 2009 – Barrier Island Disintegration Threshold

Scenarios Evaluated (page XV) – Barrier island disintegration and wetland loss defined by Figures ES1 and ES2
Scenario 1 – 20th century rate is 3 to 4 mm per year on the Mid-Atlantic Coast
Scenario 2 – 20th century SLR rate plus 2 mm per year: moderate beach erosion, wetlands conversion to open water, and unrecoverable barrier island disintegration.
Scenario 3 – 20th Century SLR rate plus 7 mm per year: Widespread, almost total beach erosion, wetlands conversion to open water and unrecoverable barrier island disintegration.

Interpretation: In 2009, the US Global Change Research Program report, Coastal Sensitivity to Sea Level Rise, Focus on the Mid-Atlantic Region, identified that most of the low-profile beaches and coastal wetlands along the mid-Atlantic coast were already eroding and being degraded by sea level rise beyond the threshold of beach and wetlands regeneration, with 3 to 4 mm of sea level rise per year. This report defines the impacts of three scenarios of sea level rise rate: 20th century rate, 20th century plus 2 mm per year and 20th century plus 7 mm per year.

Global Relevance – Because coastal barrier islands around the world are quite similar, degradation and disintegration behaviors can be assumed to be similar.
Figure ES1, page 3 and ES2, page 4 illustrate the beach degradation and wetland submergence scenarios from this report. Geographic extents include North Carolina through New York. The following is a summary of conditions shown in these two figures:

— Existing conditions in 2009: 3 to 4 mm sea level rise, about 90% of beaches are being degraded by overwash, erosion and island breaching. A threshold condition may already exist for the most vulnerable category where barrier island segmentation and disintegration could be occurring. Five percent of existing wetlands have been converted to open water and 15 to 20% could be threatened.
— With 2 mm additional sea level rise or 5 to 7 mm rise per year, thresholds condition develop for barrier island segmentation and disintegration on about 25% of barrier islands and could develop across another 25%.  Existing wetlands converted to open water increases to 15 to 20% and an additional 80 percent could be threatened.
— With 7 mm additional sea level rise, or 10 to 11 mm of sea level rise per year, thresholds condition develop for barrier island segmentation and disintegration on about 60% of barrier islands and could develop across another 30%.  Existing wetlands converted to open water increases to 85% and an additional 5 % could be threatened.

Low-profile beach geometry is similar for most of the Gulf and East Coasts, so this document can serve as a guide to current and future sea level rise degradation of beaches and wetlands along most of the heavily populated US coast, because most of the US coast -by mileage- consists of low profile beaches. (Heavily populated excludes Alaska, and Louisiana is a special case.)
US Climate Change Science Program 2009, Coastal Sensitivity to Sea Level Rise – Focus on the Mid-Atlantic Region, Washington, DC: US Environmental Protection Agency.

IPCC 2014 – The sea level rise adaptability limit… >From the IPCC Working Group II Report 2014, “Nicholls et al. (2011) show that only a limited number of adaptation options are available for specific coastal areas if sea level exceeds a certain threshold (1 m) at the end of the century.”
Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects.  Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, page 393, paragraph 10.

Unrecoverable resource abandonment by 2035… NOAA’s 2017 Sea level rise report tells us that we can expect 9 inches of sea level rise by 2030. The Union of Concerned Scientists report on the NOAA report tells us that with 9 inches of sea level rise, we will see resource abandonment as chronic nuisance flooding increases 25 times. This amount of sea level rise increase will create conditions where normal high tide nuisance flooding of 0.5 m more than the normal high tide, with 9 to 14 inches of sea level rise by 2030 under the worst-case scenario, increases in frequency from once every five years to once every 2.4 months, on average. UCS “By 2035, the number of EICs nearly doubles (to 167) compared to today with the Intermediate-High scenario. That number rises to 272, 365, and 489 in the years 2060, 2080, and 2100”
UCS summary page –

NOAA 2017 – Global and Regional Sea Level Rise Scenarios for the United States, 14″ sea level rise by 2030, intermediate-high scenario (not extreme scenario)… NOAA defines this rate of tidal flooding as when the 5-year tide becomes the tide that happens five or more times per year. “The median value in Figure 15d is about 0.35 m, with a range from about 0.1 m to 1.1 m. Thus, for most of U.S. tide gauge locations examined (108 locations; 90 along U.S. coastlines outside Alaska), with an additional 0.35-m rise (<14 in) in RSL, exposure to disruptive/damaging tidal flooding will become much more commonplace.” … “Considering RSL under the Low, Intermediate-Low, Intermediate and Intermediate-High scenarios (Figure 16a–d), disruptive/damaging tidal flooding will occur five or more times a year at most locations (90 cities) along the U.S. coastline (outside Alaska) by or about (±5 years) 2080, 2060, 2040 and 2030, respectively.”

NOAA 13.1 feet of Sea Level Rise by 2100 (100-year GMSL (Global Mean Sea Level), or the normal annual tide with a one-percent chance of occurrence)… By 2070, the one-percent mean sea level (100-year event) is projected to be 7.8 feet higher than today. By 2100, NOAA projects the ocean could be as much as 13.1 feet higher. This is for Key West and not radically dissimilar for much of the rest of the US. (Figure 17, page 40). “The Low scenario has a 94% to 100% chance of being exceeded under RCP2.6 and RCP8.5, respectively, whereas the Extreme scenario has a 0.05% to a 0.1% chance of being exceeded. New evidence regarding the Antarctic ice sheet, if sustained, may significantly increase the probability of the Intermediate-High, High, and Extreme scenarios, particularly for RCP8.5 projections based upon Kopp et al. (2014). These ice-sheet modeling results have not yet been incorporated into a (conditional) probabilistic analysis of GMSL.” (page 21)
Sweet et al., Global and Regional Sea Level Rise Scenarios for the United States, NOAA, January 2017.