Understanding Uncertainty in Climate Change and Sea Level Rise, with Vivek Srikrishnan – Resources Magazine

Report on Future Sea-Level Rise Projections and Geophysical Uncertainties

Introduction: Sea-Level Rise and the Urgency for Climate Action (SDG 13)

A recent study, “The Interplay of Future Emissions and Geophysical Uncertainties for Projections of Sea-Level Rise,” by Vivek Srikrishnan and coauthors, provides a comprehensive analysis of the long-term risks associated with rising sea levels. The findings underscore the critical importance of immediate and decisive climate action, as outlined in Sustainable Development Goal 13 (Climate Action), to mitigate catastrophic impacts on coastal communities, ecosystems, and global stability. The report highlights how unchecked sea-level rise directly threatens progress on numerous SDGs, including SDG 11 (Sustainable Cities and Communities) and SDG 14 (Life Below Water).

Key Drivers and Uncertainties in Sea-Level Rise Projections

The uncertainty in projecting future sea-level rise stems from three primary sources of human-induced change:

1. Thermal Expansion of Oceans: As oceans absorb heat due to global warming, the water expands. While this process is a significant contributor, it is considered relatively predictable compared to other factors.
2. Ice Melt: The melting of glaciers and, more critically, the vast ice sheets of Greenland and Antarctica, introduces new water into the oceans. This is the largest source of long-term uncertainty.
3. Changes in Land-Water Storage: Human activities such as reservoir management and groundwater depletion alter the amount of water stored on land, eventually affecting sea levels.

The Critical Role of Ice Sheets in Long-Term Uncertainty

The response of polar ice sheets to warming is the most significant and least understood variable in sea-level rise projections. The potential contributions are immense and pose a direct threat to achieving SDG 14 (Life Below Water) by altering ocean salinity and currents.

• Greenland Ice Sheet: Complete melting would result in approximately 7 meters of global mean sea-level rise.
• West Antarctic Ice Sheet: Complete melting would contribute about 3 meters.
• East Antarctic Ice Sheet: Complete melting would lead to a catastrophic 53 meters of rise, though this is considered a very long-term and less probable risk.

Uncertainty is compounded by complex feedback mechanisms, such as the ice-albedo effect, and localized physical dynamics. For instance, changes in ocean water stratification can either accelerate or buffer melt rates, making precise predictions challenging. The inertia within these massive ice systems means that their response to temperature changes is delayed, creating a “memory” of past climate conditions that complicates forecasting.

Analysis of Future Emissions Scenarios and Geophysical Uncertainties

The Significance of Emission Pathways over Cumulative Totals

The study emphasizes that the rate and timing of greenhouse gas emissions are more critical for future sea-level rise than the cumulative total of emissions. A scenario with a high near-term emissions peak, even if followed by rapid reductions, poses a greater risk than a scenario with steadily controlled emissions. This is because higher temperatures, even for a short period, can trigger irreversible feedback loops and instabilities in the ice sheets. This finding reinforces the urgency of immediate mitigation efforts as called for by SDG 13, suggesting that delaying action increases the risk of crossing critical tipping points.

Modeling a Full Pipeline of Uncertainties

The research incorporates a full spectrum of uncertainties to link mitigation choices with adaptation needs, a crucial step for informing policies related to SDG 9 (Industry, Innovation, and Infrastructure) and SDG 11.

• Emissions Trajectories: Uncertainty in the timing and rate of future emissions reductions.
• Carbon Cycle: The capacity of natural sinks to absorb CO2.
• Climate Response: Key variables including Equilibrium Climate Sensitivity (the planet’s long-term warming response to a doubling of CO2), ocean heat uptake, and the cooling effect of aerosols.
• Sea-Level Response: Uncertainties in how ice sheets, thermal expansion, and land-water storage respond to warming.

Projected Outcomes and Implications for Sustainable Development

Projections for 2100 and 2200 under Varying Scenarios

The report analyzed optimistic, baseline, and pessimistic emissions scenarios, revealing starkly different long-term futures. While differences by 2050 are minimal—indicating that near-term sea-level rise is largely locked in and requires adaptation—the divergence grows significantly thereafter.

• By 2100: Median global mean sea-level rise ranges from 0.25 meters to nearly 3 meters across scenarios, with the pessimistic scenario concentrating probability at the higher end. This variability has profound implications for the resilience of coastal infrastructure and communities, central to SDG 11.
• By 2200: The divergence becomes extreme. The median sea-level rise is approximately 1 meter in the optimistic scenario, 2 meters in the baseline, and 3 meters in the pessimistic scenario. However, the uncertainty range is vast, with the high end of the pessimistic scenario projecting 6 to 8 meters (18 to 24 feet) of rise, which would render many of the world’s major coastal cities uninhabitable.

Ranking Key Uncertainties Over Time

The relative importance of different uncertainties changes over time.

1. Near-Term (to ~2070): Equilibrium Climate Sensitivity and the response of the Greenland ice sheet are the dominant sources of uncertainty.
2. Long-Term (Post ~2070): The stability of the Antarctic ice sheet becomes a critical uncertainty. At this point, emissions uncertainty—specifically, the timing of peak emissions—becomes the most important factor humans can control, as it determines whether Antarctic instability thresholds are crossed.

Policy Implications for Achieving the Sustainable Development Goals

Prioritizing Greenhouse Gas Reductions

The analysis suggests that reducing short-lived but potent greenhouse gases like methane is critical. While CO2 is the primary long-term driver, the intense short-term warming from methane increases the risk of crossing irreversible ice-sheet tipping points. This reinforces the need for a comprehensive climate strategy under SDG 13 that addresses all greenhouse gases to maintain a “safe operating space” and avoid uncontrollable geophysical responses.

The Imperative for Adaptation and Resilient Infrastructure (SDG 9 & SDG 11)

Given that significant sea-level rise is unavoidable in the coming decades, mitigation efforts alone are insufficient. A dual strategy is required. Aggressive emissions reduction must be paired with immediate investment in adaptation measures and resilient infrastructure, as mandated by SDG 9 and SDG 11. Protecting vulnerable coastal populations, who are often the most disadvantaged, is essential for achieving SDG 1 (No Poverty) and ensuring a sustainable and equitable future for all.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

   The article on sea level rise and its underlying uncertainties connects to several Sustainable Development Goals (SDGs). The primary connections are with goals concerning climate change, marine ecosystems, and the safety of human settlements.

   • SDG 13: Climate Action: This is the most central SDG addressed. The entire article discusses the causes and consequences of climate change, focusing on sea level rise as a major impact. It explores the role of greenhouse gas emissions (carbon dioxide, methane), global temperature increases, and the urgent need for mitigation and adaptation strategies. The discussion on different emissions scenarios (“optimistic,” “baseline,” “pessimistic”) directly relates to the global effort to combat climate change.
   • SDG 14: Life Below Water: The article directly addresses the health and state of the oceans. It identifies “thermal expansion of the ocean” as a primary driver of sea level rise, which is a fundamental change to marine environments. Furthermore, it discusses how “warm ocean waters” contribute to the melting of sea-based ice sheets in Antarctica, highlighting the direct impact of ocean warming on global systems and coastal ecosystems.
   • SDG 11: Sustainable Cities and Communities: The threat of sea level rise has profound implications for coastal cities and communities. The article’s projections of several meters of sea level rise (“six to eight meters depending on the scenario… at the high end”) imply catastrophic risks for coastal infrastructure, housing, and populations. The mention of local factors like “subsidence due to aquifer depletion” in places like Norfolk underscores the vulnerability of specific urban areas to this climate-related disaster.
   • SDG 7: Affordable and Clean Energy: While not the main focus, this SDG is implicitly linked. The root cause of the climate change discussed is greenhouse gas emissions, which are largely driven by the global energy system. The article’s emphasis on the need to “reduce emissions as soon as possible” and the mention of a “decarbonization silver bullet” point directly to the necessity of transitioning to clean energy sources to mitigate the worst impacts of sea level rise.

2. What specific targets under those SDGs can be identified based on the article’s content?

   The article’s detailed discussion allows for the identification of several specific SDG targets.

   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries. The article explicitly states that in the near term, some level of sea level rise is locked in, noting, “we kind of need to adapt our way out of things in the next few decades. We can’t mitigate our way to reducing sea level risk.” This directly points to the necessity of building adaptive capacity to the hazard of rising seas.
   • Target 13.2: Integrate climate change measures into national policies, strategies and planning. The analysis of different emissions trajectories (baseline, optimistic, pessimistic) and the finding that the “timing of when we decrease emissions becomes more important” are central to the formation of effective climate policy and long-term strategic planning to limit global warming and its consequences.
   • Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts… The article describes fundamental physical changes to the ocean, including thermal expansion and warming waters that melt ice sheets. These are significant adverse impacts that alter marine and coastal environments, making this target highly relevant.
   • Target 11.5: By 2030, significantly reduce the number of deaths and the number of people affected and substantially decrease the direct economic losses…caused by disasters, including water-related disasters… Sea level rise is a slow-moving, water-related disaster. The projections of up to “18 to 24 feet of potential sea level rise by 2200” represent a massive future disaster for coastal communities, directly aligning with the goal of this target to reduce the impact of such events.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

   Yes, the article is rich with quantitative data and concepts that serve as direct or implied indicators for measuring the scale of the climate problem and progress towards the identified targets.

   • Global Mean Sea Level Rise (in meters): This is the primary indicator discussed. The article provides specific projections for different scenarios and timeframes, such as medians of “about two meters of sea level rise” in the baseline scenario by 2200, with an uncertainty range up to “six to eight meters.” This metric directly measures the severity of the climate hazard mentioned in Targets 13.1 and 11.5.
   • Global Temperature Anomaly (in degrees Celsius): The article links emissions to temperature, a key indicator of climate change. It projects median warming of “about 2°C” in the optimistic scenario and “2.7°C in the pessimistic scenario” by 2100. This indicator is fundamental to tracking progress on climate mitigation (Target 13.2).
   • Greenhouse Gas Emissions Trajectories: The article uses different emissions scenarios (e.g., SSP2-4.5, SSP5-8.5) as a framework for its analysis. These pathways are themselves indicators of global policy choices and mitigation efforts. The discussion of the importance of the “timing of when we decrease emissions” implies that the peak emissions year and the rate of reduction are critical indicators.
   • Rate of Ice Sheet Melt: The article identifies the melting of Greenland and Antarctic ice sheets as a major contributor to sea level rise and a source of uncertainty. The rate of melt and the stability of these ice sheets are critical physical indicators of climate change’s impact on the planet’s systems, relevant to both SDG 13 and SDG 14.

4. Create a table with three columns titled ‘SDGs, Targets and Indicators” to present the findings from analyzing the article. In this table, list the Sustainable Development Goals (SDGs), their corresponding targets, and the specific indicators identified in the article.

   SDGs	Targets	Indicators
   SDG 13: Climate Action	13.1: Strengthen resilience and adaptive capacity to climate-related hazards.	Projected global mean sea level rise (e.g., medians of 1-3 meters by 2200, with high-end uncertainty up to 6-8 meters).
   SDG 13: Climate Action	13.2: Integrate climate change measures into national policies, strategies and planning.	Greenhouse gas emissions scenarios (e.g., SSP2-4.5, SSP5-8.5); Global temperature increase projections (e.g., 2°C to 2.7°C by 2100).
   SDG 14: Life Below Water	14.2: Sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts.	Thermal expansion of the ocean; Rate of ice sheet melt due to warm ocean waters.
   SDG 11: Sustainable Cities and Communities	11.5: Significantly reduce the number of people affected and economic losses from water-related disasters.	Projections of global and local sea level rise (e.g., high-end risk of 18-24 feet by 2200), indicating the scale of the threat to coastal settlements.

Source: resources.org