Sea level rise

Understanding the Rising Tide

The Earth’s oceans are rising, and it’s a phenomenon that affects us all. Between 1901 and 2018, sea levels rose by 15–25 cm (6–10 in), but this rate has accelerated to an alarming 4.62 mm per year for the decade from 2013 to 2022 due to human activities. This rapid increase is a stark reminder of our changing climate and its profound impact on coastal communities worldwide.

The Drivers of Sea Level Rise

What exactly causes this rise in sea levels? The melting ice sheets and glaciers account for 44% of the observed rise between 1993 and 2018, while thermal expansion of water accounts for a significant 42%. This means that as the Earth warms, the oceans absorb more heat, causing them to expand. But it’s not just about ice melting; changes in land use and water storage also play a role.

Future Projections

By 2100, projected sea level rise could be anywhere from 30 cm (1 ft) to 1.9 m (6.2 ft), with high emissions accelerating this further. This means that coastal populations face a future where flooding, increased storm surges, and vulnerability to tsunamis are real threats. Local factors like tidal range or land subsidence can exacerbate these impacts, making the situation even more complex for vulnerable communities.

Adaptation Strategies

How do we adapt? Hard-construction practices such as building levees and sea walls are one approach. Dune rehabilitation, beach nourishment, and managed retreat are other strategies that can help mitigate the effects of rising seas. Poorer nations may struggle to implement these adaptation measures due to financial constraints, but societies with resources can take proactive steps.

Caribbean and Pacific Islands at Risk

The low-lying Caribbean and Pacific islands could become uninhabitable later this century if greenhouse gas emissions are not reduced. This is a dire warning that underscores the urgency of global action to curb climate change. Adaptation strategies must be carefully chosen, considering the resilience and adaptive capacity of ecosystems and countries.

Modeling Sea Level Rise

How do scientists predict future sea level rise? Several approaches are used for modeling. Process-based models compute ice melting and rising sea temperatures through ice-sheet and general circulation models, while semi-empirical methods apply statistical techniques to observed data. Structured expert judgment combines the opinions of many scientists to determine likely outcomes.

Uncertainty and Projections

The Intergovernmental Panel on Climate Change (IPCC) provides several plausible scenarios for 21st-century sea level rise, depending on future greenhouse gas emissions. These range from a minimum of 28-61 cm by 2100 under the Representative Concentration Pathways (RCPs) to 32-101 cm under the Shared Socioeconomic Pathways (SSPs). The greatest uncertainty lies in processes like Marine Ice Sheet Instability and Marine Ice Cliff Instability, which can accelerate ice loss.

Historical Context

How has sea level changed historically? In the recent geological past, thermal expansion from increased temperatures and changes in land ice were the dominant reasons for sea level rise. The last time Earth was 2 °C warmer than pre-industrial levels was during the Eemian interglacial period, when sea levels were at least 5 m higher.

Current Measurement Techniques

Tide gauges and satellite measurements provide crucial data on sea level changes. Tide gauges measure relative sea level, while satellites measure absolute changes. Since the launch of TOPEX/Poseidon in 1992, altimetric satellites have been continuously recording sea level and its changes.

Regional Variations

Why do regional variations exist? Differences in ocean water amounts or land elevation changes drive these variations. Researchers factor in Earth’s deformations, gravity, and rotation for precise measurements. Satellite measurements estimated a rate of sea level rise from 1993 to 2017 at 3.0 ± 0.4 millimeters per year.

Future Projections

The future projections for sea level rise are alarming, with estimates ranging from 6-7 meters at a warming peak of 1.5°C over 10,000 years to 28-37 meters at a warming peak of 5°C over the same period. The world’s largest potential source of sea level rise is the East Antarctic Ice Sheet (EAIS), which holds enough ice to raise global sea levels by 53.3 m. Despite a net mass gain, some glaciers have lost ice due to ocean warming and structural support decline.

Adaptation and Mitigation

How can we adapt? Cities like Miami and Shanghai are particularly vulnerable under warming of 3 °C. Adaptation plans often account for only one or two sea level rise projections, while few include four projections or assessments beyond 2100. Cutting greenhouse gas emissions can slow sea level rise after 2050 but cannot stop it outright.

Global Impact

The global impact of rising seas is significant. In Africa, future population growth amplifies risks from sea level rise. By 2060, around 185-230 million people will live in highly exposed coastal zones. In Asia, the region accounts for 70% of people exposed to sea level rise during the 21st century.

Case Studies

How are different regions adapting? In Europe, many sandy coastlines are vulnerable to erosion due to rising seas. In the Netherlands, a flexible mix of hard and soft measures is in place to cope with sea level rise. In the United States, coastal cities like New York face significant challenges, with current 100-year flood events becoming more frequent.

Conclusion

The rising tide is a global challenge that requires immediate attention. From melting ice sheets and thermal expansion to adaptation strategies and future projections, every aspect of sea level rise impacts our world in profound ways. The time to act is now, before the consequences become irreversible.