Rising Sea Levels in Antarctica LILY

RISING SEA LEVELS IN ANTARCTICA

By Lily

Global sea levels are currently rising at an average rate of 1.8 mm per year since 1961, and 3.1 mm per year since 1993. The main contributions for this rise are from melting glaciers and ice caps, and thermal expansion of the ocean. In addition, the extent of polar snow and ice cover has been receding.

Understanding the Holocene Sea level rise, helps to contextualise the rate of sea level change. The IPCC, which stands for The Intergovernmental Panel on Climate Change, is an intergovernmental body of the United Nations responsible for advancing knowledge on human-induced climate change. They have currently estimated the global sea level rise to be around 1.8 ± 0.5 mm per annum. The melting of mountain glaciers and ice caps accounts for quite a lot of this rise, and this may be because smaller glaciers, which also tend to be steeper, are more sensitive to global warming. Over the last 15 years, glaciers around the Antarctic Peninsula have contributed 0.19 ± 0.045 mm per year to sea level rise.

In 2021, the Earth’s northern ice cap showed the impacts of the climate crisis. The Arctic sea ice reached its annual minimum, at the second lowest extent seen in four decades. On 15th September 2021, the ice was measured at 3.74m sq km, which marked only the second time that the extent has fallen below 4m sq km in the current record.

The melting is likely to take place over a long period, beyond the end of this century, but is almost certain to be irreversible, because of the way in which the ice cap is likely to melt. Antarctica’s vast ice cap, which covers about as much of the earth as North America and is close to three miles (5km) thick, holds more than half of the earth’s fresh water. Some of this is floating sea ice, which does not cause sea level rises in the way of ice melting from land, but is subject to melting from above and below because of the warming sea. If temperatures rose by 4°C, which some predictions say is possible if the world fails to reduce greenhouse gas emissions quickly, then the sea level rise would be 6.5 metres from the Antarctic alone, not counting the contribution from Greenland and other glaciers. The amount of sea level rise facing coastal cities as a result of ice melt could be roughly halved, if the world meets the Paris Agreement’s toughest goal of holding climate change to 1.5°C of warming. Coastal flooding would still worsen, as meltwater from glaciers and ice sheets would raise seas by an average 13cm by 2100, however failure to harness in carbon dioxide emissions, leading to global warming of 3.4°C, would see a 25-cm increase from ice melt.

There are two primary causes of global mean sea level rise - added water from melting ice sheets and glaciers and thermal expansion. The melting of Antarctica's ice sheet is currently responsible for 20 to 25 percent of global sea level rise. When an ice mass grows on land, the weight of ice sheets pushes land downwards because the upper mantle underneath the crust is a soft viscous liquid. Once ice sheets melt, a process of isostatic readjustment occurs. In addition, some locations experience accretion and land builds up - this is isostatic sea level change.

The major physical impacts of a rise in sea level include erosion of beaches and inundation of deltas, as well as flooding and loss of marshes and wetlands. Increased salinity will likely become a problem in coastal aquifers and estuarine systems as a result of saltwater intrusion. Although there is some uncertainty about the effect of climate change on storms and hurricanes, increases in the intensity or frequency, or changes in the paths of these storms, could increase storm damage in coastal areas. Damage to, and loss of, coastal areas would threaten the economic and ecological features provided by coastal wetlands and marshes, including flood control, ecological habitat and water purification. Damages and economic losses could be reduced if local decision-makers understand the potential impacts of sea-level rise and use this information for planning, in order to protect the coastline.

One of the main targets of Glaciologists and glacial Geologists is to understand the rates of sea level rise, to allow better predictions of future change. The IPCC predicts future sea level rise based on presents rates of melting and predictions of future carbon emissions and warming. However, there are large uncertainties, because the dynamic interaction of ice sheets to climate change needs to be better understood. Predictions to 2100 range from 20 cm to 2 m. The best estimate is 0.6 m, mostly from thermal expansion of the oceans and glacier melt. Accelerated ice velocities, marine ice sheet insecurities and ice shelf collapse all form part of the large uncertainties in estimating future global sea level rise.

In some instances, humans can’t control the rise in sea level. One solution that cities employ to decrease flooding from tides and storms, is constructing seawalls. These barriers are often built to a height of five to six feet above sea level and cost £5000 per metre. When seawalls age or become damaged from constant exposure to saltwater or the impact of waves, they need to be replaced. They also need to be replaced or built higher as sea levels continue to rise. Similar to seawalls, beaches and dunes can act as a natural wall and reduce the impact of storm surge. The bigger the beach or larger the dune, the more water can be stopped from reaching homes and roads. Towns can add sand to make beaches bigger or to prevent them from eroding. Using this type of natural infrastructure can protect against flooding while maintaining beaches in a sustainable way for the community to enjoy.

Sea level rise is a major indicator of ongoing global change. Modern rates of sea level rise started about 100 years ago, and it is certain that the 20th century rise is faster than rates over the preceding three millennia. The sea level has risen 8–9 inches (21–24 centimetres) since 1880 and in 2020, global sea level set a new record high of 91.3 mm (3.6 inches), above 1993 levels. However, during the Last Interglacial, rates of sea level rise were possibly higher and may have been similar to those predicted in some future climate change scenarios. The geological record of the past three glacial–interglacial cycles shows a strong relationship between atmospheric CO2 concentrations and sea level, and even if CO2 remains at its current level, sea level rises in excess of several metres are likely over the next few centuries.

www.antarcticglaciers.org/glaciers-and-climate/sea-level-rise-2/

www.theguardian.com/environment/2020/sep/23/melting-antarctic-ice-will-raise-sea-level-by-25-metres-even-if-paris-climate-goals-are-met-study-finds