Thwaites Glacier - And Drastic Sea Level Rise

Thwaites Glacier sometimes referred to as the Doomsday Glacier, is an unusually broad and vast Antarctic glacier flowing into Pine Island Bay, part of the Amundsen Sea, east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. Its surface speeds exceed 2 kilometers (1.2 miles) per year near its grounding line. Its fastest-flowing grounded ice is centered between 50 and 100 kilometers (31 and 62 mi) east of Mount Murphy. It was named by ACAN after Fredrik T. Thwaites, a glacial geologist, and geomorphologist.

Thwaites Glacier is closely watched for its potential to raise sea levels. Along with the Pine Island Glacier, it

has been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, due to its apparent vulnerability to significant retreat. This hypothesis is based on both theoretical studies of the stability of marine ice sheets and observations of large changes in these two glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces have lowered, and their grounding lines have retreated.

Since the 1980s, the Thwaites glacier, nicknamed the "Doomsday glacier", has had a net loss of over 600 billion tons of ice, though pinning of the Thwaites Ice Shelf has served to slow the process. The Thwaites Ice Shelf has acted as a dam for the eastern portion of the glacier, bracing it and allowing for a slow melt rate, in contrast to the undefended western portion.

In 2021 the ice shelf was predicted to disintegrate in a decade, and as soon as 2026. This will accelerate the melting of Thwaites Glacier by about 25%, and increase its contribution to global sea-level rise from 4% to 5%.

Research

In 2011, using geophysical data collected from flights over Thwaites Glacier (data collected under NASA's IceBridge campaign), a study by scientists at Columbia University's Lamont-Doherty Earth Observatory showed a rock feature, a ridge 700 meters tall that helps anchor the glacier and helped slow the glacier's slide into the sea. The study also confirmed the importance of seafloor topography in predicting how the glacier will behave in the near future. However, the glacier has been considered to be the biggest threat on relevant time scales, for rising seas, current studies aim to better quantify retreat and possible impacts.

Extensive calving at the marine terminus of Thwaites Glacier is monitored by remote sensing and seismological observations, with the largest events being seismically detectable at ranges up to 1600 km.

Water drainage beneath the glacier - Swamp-like canal areas and streams underlie the glacier. The upstream swamp canals feed streams with dry areas between the streams which retard the flow of the glacier. Due to this friction, the glacier is considered stable in the short term.

Sea level rise

Tide gauge measurements show that the current global sea-level rise began at the start of the 20th century. Between 1900 and 2017, the globally averaged sea level rose by 16–21 cm (6+1⁄2–8+1⁄2 in). More precise data gathered from satellite radar measurements reveal an accelerating rise of 7.5 cm (3 in) from 1993 to 2017, for an average rate of 31 mm (1+1⁄4 in) per decade. This acceleration is due mostly to climate change, which includes heating of the ocean and melting of the land-based ice sheets and glaciers. Between 1993 and 2018, the thermal expansion of water contributed 42% to sea-level rise; melting of temperate glaciers, 21%; Greenland, 15%; and Antarctica, 8%. Climate scientists expect the rate to further accelerate during the 21st century, with the latest measurements saying the sea levels are currently rising by 3.6 mm per year.

Projecting future sea levels is challenging, due to the complexity of many aspects of the climate system and to time lags in sea level reactions to Earth temperature changes. As climate research into past and present

sea levels leads to improved computer models, projections have consistently increased. In 2007, the Intergovernmental Panel on Climate Change (IPCC) projected a high-end estimate of 60 cm (2 ft) through 2099, but their 2014 report raised the high-end estimate to about 90 cm (3 ft). In February 2021, a paper published in Ocean Science suggested that past projections for global sea-level rise by 2100 reported by the IPCC were likely conservative and that sea levels will rise more than previously expected.

The sea level will not rise uniformly everywhere on Earth, and it will even drop slightly in some locations, such as the Arctic. Local factors include tectonic effects and subsidence of the land, tides, currents, and storms. Sea level rises can affect human populations considerably in coastal and island regions. Widespread coastal flooding is expected with several degrees of warming sustained for millennia. Further effects are higher storm surges and more dangerous tsunamis, displacement of populations, loss, and degradation of agricultural land, and damage in cities. Natural environments like marine ecosystems are also affected, with fish, birds, and plants losing parts of their habitat.

Contributions

The three main reasons warming causes global sea level to rise are: oceans expand, ice sheets lose ice

faster than it forms from snowfall, and glaciers at higher altitudes also melt. Sea level rise since the start of the 20th century has been dominated by the retreat of glaciers and expansion of the ocean, but the contributions of the two large ice sheets (Greenland and Antarctica) are expected to increase in the 21st century. The ice sheets store most of the land ice (∼99.5%), with a sea-level equivalent (SLE) of 7.4 m (24 ft 3 in) for Greenland and 58.3 m (191 ft 3 in) for Antarctica.

Each year about 8 mm (5⁄16 in) of precipitation (liquid equivalent) falls on the ice sheets in Antarctica and Greenland, mostly as snow, which accumulates and over time forms glacial ice. Much of this precipitation began as water vapor evaporated from the ocean surface. Some of the snow is blown away by wind or disappears from the ice sheet by melt or by sublimation (directly changing into water vapor). The rest of the snow slowly changes into ice. This ice can flow to the edges of the ice sheet and return to the ocean by melting at the edge or in the form of icebergs. If precipitation, surface processes, and ice loss at the edge balance each other, sea levels remain the same. However, scientists have found that ice is being lost and at an accelerating rate.

Effects

Current and future sea-level rise is set to have a number of impacts, particularly on coastal systems. Such impacts include increased coastal erosion, higher storm-surge flooding, inhibition of primary production processes, more extensive coastal inundation, changes in surface water quality and

groundwater characteristics, increased loss of property and coastal habitats, increased flood risk and potential loss of life, loss of non-monetary cultural resources and values, impacts on agriculture and aquaculture through a decline in soil and water quality, and loss of tourism, recreation, and transportation functions. Many of these impacts are detrimental. Owing to the great diversity of coastal environments; regional and local differences in projected relative sea level and climate changes; and differences in the resilience and adaptive capacity of ecosystems, sectors, and countries, the impacts will be highly variable in time and space. River deltas in Africa and Asia and small island states are particularly vulnerable to sea-level rise.

In addition to rising sea levels, other effects of climate change can heavily impact the influence on populations. Coastal flooding is accelerated by deforestation and change or extremes in weather conditions. Regions that are already vulnerable to the rising sea level also struggle with coastal flooding washing away land and altering the landscape. People in these areas struggle increasingly because of these different effects of climate change. Climate change-influenced storms also create a greater frequency of coastal flooding.

A 2020 review of 33 publications found that "most global estimates are in the order of tens or hundreds of millions of people exposed to coastal inundation and coastal flooding for different timeframes and scenarios" due to sea-level rise.

Long-term sea-level rise - Projections

Both the Greenland ice sheet and Antarctica have tipping points for warming levels that could be reached before the end of the 21st century. Crossing such tipping points would mean that ice-sheet changes are

potentially irreversible: a decrease to pre-industrial temperatures may not stabilize the ice sheet once the tipping point has been crossed. Quantifying the exact temperature change for which this tipping point is crossed remains controversial. For Greenland, estimates roughly range between 1 and 4 °C (2 to 7 °F) above pre-industrial. As of 2020, the lower of these values has already been passed. A 2021 analysis of sub-glacial sediment at the bottom of a 1.4 km Greenland ice core finds that the Greenland ice sheet melted away at least once during the last million years, and therefore strongly suggests that its tipping point is below the 2.5 °C maximum positive temperature excursion over that period.

A 2013 study estimated that each degree of temperature rise translates to a 2.3 m (7 ft 7 in) commitment to sea-level rise within the next 2,000 years. More recent research, especially into Antarctica, indicates that this is probably a conservative estimate and true long-term sea-level rise might be higher. Warming beyond the 2 °C (3.6 °F) target potentially leads to rates of sea-level rise dominated by ice loss from Antarctica. Continued carbon dioxide emissions from fossil fuel sources could cause additional tens of meters of sea-level rise, over the next millennia, and the available fossil fuel on Earth is even enough to ultimately melt the entire Antarctic ice sheet, causing about 58 m (190 ft) of sea-level rise.