Earth’s glaciers and ice caps (here, we differentiate from the two ice sheets, the Antarctic and Greenland ice sheets) are shrinking at an alarming rate. Each year, global glaciers are losing more mass than is being replenished in each accumulation season. 28 trillion tonnes of ice were lost from 1994 to 2017, and rates of ice loss have risen by 57% since the 1990s.
How much ice is there in the world?
Globally, Earth has 153.8 x103 gigatonnes (Gt) of ice. A gigatonne is a billion tonnes; a gigatonne of water forms a towering block of water 1 km high, 1 km wide, and 1 km deep. That is the height of Mount Snowdon in Wales! The Earth’s glaciers have enough ice to raise global sea levels by 32 cm.
Globally shrinking glaciers
At present, global glacier ice volume is shrinking at a rate of 267±16 Gt per year, and is accelerating by 48±16 Gt per decade. This is like putting 267 Mt Snowdons into the ocean, each year! Ice lost from melting contributes significantly to sea level rise, and is estimated to contribute 0.75 mm per year.
Globally shrinking ice sheets
Between 1992 and 2017, the Antarctic ice sheet lost approximately 2603±563 Gt of ice . Ice sheet loss in Antarctica has tripled since 2012, when compared with ice loss from the previous two decades . The resulting ice shelf thinning and collapse in the Antarctic Peninsula has caused the speed up of glaciers further up stream, which causes reduced ice shelf buttressing.
Ice sheets in the Arctic are experiencing similar losses to Antarctica. Between 1992 and 2018, the Greenland ice sheet lost a staggering 3902±342 Gt of ice. Roughly half of the ice lost in this period was a result of increased meltwater runoff, which had been enhanced by atmospheric warming following several unusually warm summers[5,6]. The remaining ice loss is likely to be a result of increased glacier discharge.
Between 1992 and 2017, ice loss from the Greenland and Antarctic ice sheets combined has caused global sea level to rise by 17.8±1.8 mm.
What was decided at COP26?
COP26 deliberations and decided policies will likely lead to an estimated warming of 2.6-2.7oC by 2100. However, if countries met all conditional and unconditional NDCs by 2030, warming could be reduced to 2.4oC. Current NDCs sit just below SSP 2-4.5, and well below the worst case scenarios (SSP 3-7.0 and SSP 5-8.5).
After the Paris agreement agreed to limit global warming below 1.5oC, it was predicted that almost half of global ice volume will be lost by the year 2100. Since COP26, the target for warming has increased to a maximum of 2.7oC, therefore, it is likely that over half of global ice volume will be lost by 2100.
What does this mean in terms of sea level rise?
This degree of ice melt, alongside thermal expansion, is predicted to cause sea level rise of ~56 cm by 2100. At present, sea level is rising at a rate of 3.1 mm per year. Over 680 million people live in low-lying coastal areas, which are especially susceptible to coastal flooding as a direct result of global sea level rise.
In the UK, coastal flooding is often caused by storm surges. Rising sea levels from ice melt will increase the height of sea level extremes, which will result in more frequent coastal flood events in the UK. Projected increases in coastal flooding has been strongly linked to sea level rise, and less so to changes frequency of extreme weather events and storm surges. Roughly £150 billion of assets are at risk of coastal flooding in the UK. In London alone, the number of residents at risk of tidal flooding has increased from 1.25 to 1.3 million over the past 5 years, which equates to an increase from £200 billion to £275 billion in property value. As ice loss continues to contribute to sea level rise, the risks of coastal flooding in the UK will only continue to rise.
What does this mean for water resources?
Mountain Glaciers store and provide vital water to downstream communities. Glacial retreat is threatening water security in these communities and is already causing severe water shortages in many countries that rely on mountain glaciers for a dependable water supply. Communities surrounding the Himalayas are particularly vulnerable to water shortages directly related to glacial retreat. With current COP26 NDCs, only 40% of glaciers in Central Asia will remain by 2100, threatening the lives of hundreds of millions of people.
Was COP26 a success?
Despite its praise in the media, the outcomes of COP26 are not sufficient to adequately reduce the impact of climate change on global ice loss. Even if all commitments to reduce global GHG emissions in line with SSP 2-4.5 are kept, global temperature change will exceed the threshold required to retain our life-giving glaciers.
However, COP26 was successful in one respect; there was a universal commitment to reduce global greenhouse gas emissions, and a global acknowledgment of the climate crisis. This is an important milestone.
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