Sea-level rise is a major effect of climate change, drawing international attention due to the serious impacts it could cause in various parts of the world. It is one of the most significant effects of climate change, with high projected rates of future sea-level rise capturing global attention. Particularly, countries located in low-lying areas and small islands are concerned that their land areas will decrease due to inundation and coastal erosion, potentially leading to significant population displacement. Therefore, this issue has resulted in heightened international attention as the effects of climate change become increasingly apparent.
Global average sea level has risen by 8–9 inches (21–24 centimeters) since 1880. In 2022, global average sea level set a new record high at 101.2 mm (4 inches) above 1993 levels. The rate of global sea level rise is accelerating: it has more than doubled from 0.06 inches (1.4 millimeters) per year throughout most of the twentieth century to 0.14 inches (3.6 millimeters) per year from 2006–2015.
The latest scientific understanding has been systematically assessed by the Intergovernmental Panel on Climate Change (IPCC). Since its establishment in 1988, the IPCC has published four major assessment reports. The projected future sea-level rises by 2100, as outlined in the First to Fourth Assessment Reports, are 31–110 cm (Business as usual scenario), 13–94 cm, 9–88 cm, and 18–59 cm, respectively. In each assessment, the IPCC used different climate models and scenarios for greenhouse gas (GHG) emissions, which is the major reason for the changes in the projected rise in mean sea level. Particularly, the values given in the Fourth Assessment Report (AR4), published in 2007, are relatively low because the assessment did not account for the contribution of the Greenland Ice Sheet (GIS) and West Antarctica Ice Sheet (WAIS) due to a lack of reliable understanding of their dynamics, including collapse and outflow. Consequently, some researchers considered that these estimates might represent the low end of the future rise in sea level.
As global temperatures rise due to increasing greenhouse gas emissions, several factors contribute to changes in sea levels:
- Thermal Expansion: As the oceans absorb more heat from the atmosphere, the water expands, causing sea levels to rise. This process, known as thermal expansion, is a significant contributor to sea level rise.
- Melting Ice Sheets and Glaciers: Higher temperatures lead to increased melting of ice sheets in Greenland and Antarctica, as well as glaciers around the world. The meltwater from these ice masses flows into the ocean, contributing to rising sea levels.
- Loss of Ice Caps and Arctic Sea Ice: The loss of ice caps and Arctic sea ice also adds water to the oceans as these frozen areas melt. While melting sea ice does not directly contribute to sea level rise (since it’s already displacing water), its loss can lead to other feedback effects that contribute to rising sea levels.
- Changes in Land Ice: Changes in land ice, such as the melting of ice caps and glaciers, can also contribute to sea level rise. This can occur due to both increased melting and increased flow of ice into the ocean.
Overall, these factors combined lead to a rise in sea levels globally, with potentially severe consequences for coastal communities, ecosystems, and infrastructure. Adapting to and mitigating the impacts of sea level rise are critical aspects of addressing climate change.
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