Sea level rise
Over the course of glacial and interglacial cycles, the average sea level has fluctuated, rising above and dropping below its current level. However, greenhouse gases released by human activities are disrupting this balance. Since 1850, global warming has intensified the rise in average sea level.
This accelerated rise exacerbates other climate phenomena like coastal erosion and submergence, with significant consequences for infrastructure, the natural environment and communities in coastal regions.
Global sea level
The global “absolute” or “mean” sea level is measured relative to the centre of the Earth. It represents the average global sea level. This average is calculated over a large spatial and time scale and omits occasional fluctuations and localized differences in sea level.
Relative sea level
Relative sea level refers to the overall variation in sea level relative to the vertical variation of land. Relative sea level change is the combination of global “absolute” sea level change and the local geological land movement associated with the glacial context of the region.
Factors causing sea level rise
Climate change contributes to sea level rise. Several factors explain this:
Global factors:
Thermal expansion of the oceans
When the water in the seas and oceans warms up, it expands. Warmer water increases in volume, contributing to rising sea levels.
The movement of the Earth’s crust
Since the last ice age, the Earth’s crust has been moving. In some regions, its sinking accentuates the rise in average sea level, while elsewhere, its rise can compensate for or limit the anticipated sea level rise.
Freshwater contributions
Rising temperatures are accelerating the melting of glaciers and ice caps, releasing large amounts of fresh water into the oceans and causing sea levels to rise.
The influence of the glacial context on the relative sea level rise un Quebec
In Canada, relative sea level varies depending on local geological processes, such as postglacial adjustment, which is the progressive movement of the Earth’s crust occurring due to the melting of ice after the last ice age. This melting relieved the pressure the ice was exerting on the ground, so it gradually rises or sinks.
Note that this postglacial adjustment is not uniform across all of Quebec. In areas where the ice was thicker, such as in Nunavik, the Earth’s crust is slowly rising. In response to this rise, regions around the periphery, like the Magdalen Islands, are sinking. This vertical movement of the land influences the relative sea level: the land’s rise can mitigate the rise in sea levels, while its subsidence can accentuate the effects.
Local factors
Changes in surface and deep ocean circulation
The construction of water retention infrastructure such as dams and reservoirs
Changes in the dynamics of evaporation from water bodies
Infiltration into aquifers
The tidal force of the moon
Local atmospheric circulation (wind, precipitation and atmospheric pressure)
A fragile balance between oceans and the climate
Seas and oceans cover more than 70% of the Earth’s surface and play a vital role in regulating the global climate. The global climate also significantly influences the level of seas and oceans. For example, the oceans absorb a large proportion of the CO₂ emitted by human activities. However, global warming is causing the thermal expansion of ocean water and the melting of ice, leading to a rise in absolute sea level.
