How Will Sea Levels Change in the Future?

Sea Level Will Continue to RiseSea Level Will Continue to Rise

The global sea level is rising due to human-caused climate change warming the planet. The planet warming is linked to greenhouse gas emissions. Thus, the more greenhouse gases that get added to the atmosphere, the more the global sea level will rise.

How much it rises will depend on the amount of greenhouse gases added to the atmosphere moving forward. To explore the possibilities, scientists use emission scenarios or Shared Socioeconomic Pathways (SSPs). These show the possible range, from low to high, for the amount of greenhouse gases added to the atmosphere between now and 2100. The latest Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) from August 2021 used these emission scenarios to project sea level rise by 2100 and beyond. In addition, sea level projections for different amounts of global surface temperature warming in 2100 were also created.

What are Shared Socioeconomic Pathways?What are Shared Socioeconomic Pathways?

The Shared Socioeconomic Pathways (SSPs) are scenarios used to explore how different levels of socioeconomic development and climate policies may impact future greenhouse gas emissions and, consequently, climate outcomes such as sea level rise. They were developed to provide a consistent framework for climate modeling and impact assessment, considering factors like population growth, economic development, technological progress, and climate policy efforts.

Overview of Key SSPs Used in Sea Level Projections

1. SSP1-1.9 and SSP1-2.6 (Sustainability and Low Emissions)

   • Description: These scenarios represent a world focused on sustainable development, with global efforts to curb emissions and achieve climate goals, including significant investments in renewable energy, improved energy efficiency, and lower deforestation rates. Population growth stabilizes, and societies emphasize equitable and environmentally conscious economic growth.
   • Climate Outcome: Global warming is limited to well below 2°C, with SSP1-1.9 targeting a temperature rise close to 1.5°C and SSP1-2.6 aiming for around 2°C.

2. SSP2-4.5 (Middle-of-the-Road Scenario)

   • Description: This scenario represents a world with moderate and uneven progress toward sustainability. Population and economic growth follow historical trends, and while some climate policies are implemented, they are insufficient to achieve the most ambitious climate goals. Energy and resource use remain moderate, and global efforts to mitigate emissions are mixed.
   • Climate Outcome: Global warming stabilizes around 2.7°C by 2100, resulting in intermediate levels of sea level rise.

3. SSP3-7.0 (Regional Rivalry and High Emissions)

   • Description: This scenario envisions a world with high population growth, limited international cooperation, and regional conflicts over resources. Nations prioritize economic development over environmental concerns, leading to heavy reliance on fossil fuels and limited climate action. Societies are fragmented, and efforts to reduce emissions are minimal.
   • Climate Outcome: Global temperatures rise significantly, reaching about 3.6°C by 2100. The lack of global climate action and continued high emissions contribute to more severe impacts.

4. SSP5-8.5 (Fossil-Fueled Development and Very High Emissions)

   • Description: This scenario describes a world focused on rapid economic growth, driven by extensive use of fossil fuels. There is little emphasis on sustainability or reducing emissions, with continued high energy demand and minimal climate policies. Technological innovation focuses more on economic gains than environmental protection.
   • Climate Outcome: Global temperatures could increase by more than 4°C by 2100. The high emissions under SSP5-8.5 represent a worst-case scenario with severe consequences for global sea levels and ecosystems.

What If We Stop Adding Greenhouse Gases?What Happens If We Stop Adding Greenhouse Gases?

Even if we stop all greenhouse gas emissions today, the global sea level will continue to rise over the next few centuries. This will happen no matter when greenhouse gas emissions stop. This is because Earth’s climate is very large and complex. It takes time to cycle through changes and to reach a new balance.

Think of driving a car with no brakes. Right now our foot is on the accelerator slowly speeding us up as we add greenhouse gases to the atmosphere. If we take our foot off the accelerator, the car won’t stop right away. It takes some time to roll to a stop. Similarly, if we stopped greenhouse gas emissions today or removed some greenhouse gases from the atmosphere, the heat added to the planet needs time to rebalance and cycle out. And as long as the planet is warmer, land ice will melt and ocean water will expand, rising the global sea level.

What are Low Confidence Projections vs. Medium Confidence Projections?What are Low Confidence Projections vs. Medium Confidence Projections?

In the IPCC's Sixth Assessment Report (AR6), projections of sea level rise are presented with varying levels of confidence to reflect the degree of scientific understanding and the robustness of the evidence. Low confidence projections are associated with scenarios or outcomes for which there is unknown certainty due to a lack of comprehensive data, limited agreement among models, or fundamental gaps in scientific knowledge. These projections often include factors that are difficult to quantify, such as the potential for rapid and irreversible ice sheet loss. Consequently, low confidence projections highlight areas where future research and observations are needed to better constrain estimates. On the other hand, medium confidence projections are based on a moderate level of understanding, with models generally agreeing on key processes but still subject to significant uncertainties. While the evidence base is stronger than that for low confidence projections, medium confidence estimates still warrant caution, as they reflect limitations in predicting complex interactions within the climate system, such as ice sheet dynamics and regional variability in sea level rise. Compared to the table above, the SSP5-8.5 Low Confidence scenario that includes that possibility of rapid ice sheet loss and ice sheet instabilities has a projection of 88 cm in 2100 with a Likely Range of 63 to 160 cm.

Dive Deeper: How are the IPCC AR6 projections created and how do they differ from one location to the next.

Next: What are the impacts of sea level change?