Climate-change–driven accelerated sea-level rise detected in the altimeter era
Satellite altimetry has shown that global mean sea level has been rising at a rate of ∼3 ± 0.4 mm/y since 1993. Using the altimeter record coupled with careful consideration of interannual and decadal variability as well as potential instrument errors, we show that this rate is accelerating at 0.084 ± 0.025 mm/y2, which agrees well with climate model projections. If sea level continues to change at this rate and acceleration, sea-level rise by 2100 (∼65 cm) will be more than double the amount if the rate was constant at 3 mm/y.
The relationship between greenhouse-gas forcing, global mean temperature change and sea-level rise due to thermal expansion of the oceans is investigated using upwelling–diffusion and pure diffusion models. The sensitivities of sea-level to short-timescale forcing and deep-water formation rate changes are examined. The greenhouse-gas-induced thermal expansion contribution to sea-level rise between 1880 and 1985 is estimated at 2–5 cm. Projections are made to the year 2025 for different forcing scenarios. For the period 1985–2025 the estimate of greenhouse-gas-induced warming is 0.6–1.0 °C. The concomitant oceanic thermal expansion would raise sea level by 4–8 cm.
Observations provide unequivocal evidence that global mean sea level has been rising over the past century, but that the rate of sea-level rise has significant regional variability. The key question for planners is how much sea level will rise in their region in an increasingly warm future world. Most projections are based on knowledge of the current contributions to sea-level change and assumptions about future warming and the behavior of key geophysical processes.
The sea-level rise associated with global warming is a growing concern for the scientific community as well as for governments, the media and the public. Climate-driven sea-level rise has a direct impact on the coastal zones, with threatening consequences for the ecosystem and urbanisation.
The rise in sea levels is linked to three primary factors, all induced by this ongoing global climate change:
- Thermal Expansion: When water heats up, it expands. About half of the past century’s rise in sea level is attributable to warmer oceans simply occupying more space.
- Melting Glaciers and Polar Ice Caps: Large ice formations, like glaciers and the polar ice caps, naturally melt back a bit each summer. In the winter, snows, primarily from evaporated seawater, are generally sufficient to balance out the melting. Recently, though, persistently higher temperatures caused by global warming have led to greater-than-average summer melting as well as diminished snowfall due to later winters and earlier springs. This imbalance results in a significant net gain in the ratio of runoff to ocean evaporation, causing sea levels to rise.
- Ice Loss from Greenland and West Antarctica: As with the glaciers and ice caps, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt at an accelerated pace. Scientists also believe meltwater from above and seawater from below is seeping beneath Greenland’s and West Antarctica’s ice sheets, effectively lubricating ice streams and causing them to move more quickly into the sea. Higher sea temperatures are causing the massive ice shelves that extend out from Antarctica to melt from below, weaken, and break off.
Italy could be COMPLETELY SUBMERGED by the sea at the end of the century
Belinda Robinson Chief Executive Universities Australia Feb 16, 2017
The rise in the sea level will change the morphology of the Italian coasts over the next 80 years, a study found.
And up to 5,500 square kilometres of coastal plains could end up under water – meaning Italy could be completely submerged by the end of the century.
A study by the Laboratory of Climate Modelling and the journal Quaternary Science Reviews focused on four sensitive areas of the Italian peninsula which will feel the impact of rising sea levels.
These were the North Adriatic, the Gulf of Taranto, the Gulf of Oristano and the Gulf of Cagliari.
The analysis took into account the most recent projections of sea-level rise between a minimum of 53cm and a maximum of 97cm, also including the effects due to geological and geomorphological changes.
Fabrizio Antonioli, the director of research at the Laboratory of Climate Modelling and Impact of ENEA told National Geographic Italian: “The coast is flat and there are no dunes to act as a natural barrier “Some areas are already close to or below the sea level.”
Experts suggest that the way to solve the issue is that governments will need to improve the efficiency of the dams to protect the coasts.
If no reinforcement measures are implemented in the near future, the cities of Aquileia Adria, Ravenna and Rovigo will be at risk of flooding while the coastline could arrive less than 10km from FerraraClimate change experts fear that by the year 2100, the maximum elevation calculated will be approximately 101 cm above the current sea level for the North Adriatic.
Furthermore, it will be 96cm for the Gulf of Cagliari, 95cm for Oristano and 92cm for the Gulf of Taranto.
The coastline near Venice could also go back 30 kilometres and the area between Trieste and Venice is one of the most vulnerable.
As scientists attempt to find solutions, it seems that even limiting green house gases will not mark change.
The sea level is still expected to increase by 0.5 metres during the twenty-first century, which could reach a meter or more if no drastic action is taken.