2.2.1 Melting ice and rising seas

"Sea level is rising much faster and Arctic sea ice cover shrinking more rapidly than we previously expected. Unfortunately, the data now show us that we have underestimated the climate crisis in the past." Stefan Rahmstorf, Professor of Physics of the Oceans, Potsdam University

As atmospheric conditions get hotter, the water in our oceans heats up too. Indeed, over 90% of the increased heat trapped in our atmosphere is being stored in the oceans. In 2019, the heat in the world’s oceans reached a new record level, confirming "irrefutable and accelerating2 heating of the planet. It has been calculated that the heat energy being absorbed by the oceans is the equivalent of between 3 to 6 Hiroshima-size atomic bombs every second.

All this this extra heat causes the water to expand and take up more space, resulting in rises in sea levels.

Temperature and Sea Levels Since 1880, both of which have increased since 1880

In addition, hotter water in our oceans, along with hotter air in our atmosphere, leads to the melting of sea ice, ice sheets and mountain glaciers. Fortunately, when sea ice melts it doesn’t affect sea levels - just like how an ice cube melting in a glass of water doesn’t cause the water level to go up. However, when land-based ice sheets and glaciers melt, the water runs off into the sea, causing sea levels to rise - just like what would happen if you added another ice cube to the glass of water and waited for it to melt.

In the Arctic, the area covered by sea ice in the summer has shrunk by 40% since 1979 and is now declining at a rate of 12.8% per decade. Compared to the average sea ice cover between 1981 and 2010, we have now lost about two million square km of ice - that’s an area larger than Alaska and California combined. As of July 2020 the sea ice was yet again at a record low for the time of year, and this year may break the record for lowest annual minimum previously set in 2012. Arctic sea ice is what polar bears use to hunt seals on, so they are now being forced to forage on land where they have difficulty in finding prey. Dr Steve Amstrup, chief scientist at conservation organisation Polar Bears International warned: "If we allow the sea ice loss to continue, all the polar bears will soon be gone."

The Greenland ice sheet, the second largest in the world, is losing ice seven times faster than in the 1990s, whilst the Antarctic ice sheet has lost three trillion tonnes of ice in the past 25 years and is now losing 252 billion tonnes a year - that’s six times more than it was 30 years ago.

Overall, over the past 40 years the amount of ice we have lost from our planet averages out to the loss of around 300 double-decker-sized chunks of ice... EVERY SECOND.

What’s even more concerning is the fact that the scale and speed of ice sheet loss is faster than models have predicted, threatening inundation for hundreds of millions of people. The Antarctic ice sheet is losing mass at an accelerating pace and it is thought that some regions may be reaching a tipping point, potentially leading to rates of sea level rise at least an order of magnitude larger than those observed now.

Dr. Louise Sime, Climate Scientist at the British Antarctic Survey, said: "This finding should be of huge concern for all those who will be affected by sea level rise. If this very high rate of ice loss continues, it is possible that new tipping points may be breached sooner than we previously thought."

The ‘fast melting’ part of the ice sheet is already showing signs of an "unstoppable and irreversible" collapse which would lock in around one metre of sea level rise. Indeed, in January 2020, scientists revealed that a massive sheet of ice in the Thwaites Glacier in West Antarctica, known as the "doomsday glacier", is melting far faster than experts had previously thought, with "huge implications" for global sea level rise. David Holland, Professor of Atmosphere and Ocean Science at NYU, said: "That is really, really bad. That’s not a sustainable situation for that glacier."

Our glaciers are melting too. Melting glaciers are not only responsible for about a third of our observed sea level rise, but mountain glaciers also store up water and release it in the dry season, making them an important source of water in mountain areas. Indeed, drainage basins from glaciated mountain ranges cover 26% of the global land surface (outside of Greenland and Antarctica), and are lived in by almost one-third of the world’s population. There are currently about 1.9 billion people across the globe living downstream of mountain glaciers, depending on water from these glaciers for irrigation, hydropower, domestic consumption and industry and who would be negatively affected by their loss.

In 2018, the World Glacier Monitoring Service reported the 30th consecutive year that global glaciers had lost mass. The European Alps have lost over a billion tonnes of ice since the year 2000 and are continuing to lose 1.2% of their mass every year. A study of the Himalayas found that glaciers there are now melting twice as fast as they were between 1975 and 2000 and are losing 8 billion tonnes of ice a year - that’s the equivalent to 3.2 million Olympic-sized swimming pools.

The Andes are estimated to be losing an even more alarming 23 billion tonnes of ice each year, with glaciers in the tropical Andes having already shrunk by 30-50% since 1970. For example, the glaciers of Bolivia shrank by 43% between 1986 and 2014. Researchers point out that these dwindling glaciers are estimated to "provide 20% to 28% of water for El Alto and La Paz. Therefore glacier loss will have a considerable impact, which will be felt particularly during the dry season, when glacial water provides the majority of urban water. The glaciers and mountain water systems also support agriculture, power generation and natural ecosystems throughout the region."

Glaciers Cumulative Mean Mass Balance 1980 to 2017
Image source: https://wgms.ch/global-glacier-state