What does COP26 mean for global glacier and ice sheet change?

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[1], and rates of ice loss have risen by 57% since the 1990s[1].

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[2]. 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.

Global ice loss. From Slater et al., 2021

Globally shrinking ice sheets

Between 1992 and 2017, the Antarctic ice sheet lost approximately 2603±563 Gt of ice [1]. Ice sheet loss in Antarctica has tripled since 2012, when compared with ice loss from the previous two decades [3]. The resulting ice shelf thinning and collapse in the Antarctic Peninsula has caused the speed up of glaciers further up stream[4], 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[1].

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[7].

What was decided at COP26?

COP26 deliberations and decided policies will likely lead to an estimated warming of 2.6-2.7oC by 2100[8]. 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).

Comparison of global emissions under IPCC, with total global emissions according
to nationally determined contributions. Winning et al., 2019.

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[8]. 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[1]. At present, sea level is rising at a rate of 3.1 mm per year[1]. 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[9]. Roughly £150 billion of assets are at risk of coastal flooding in the UK[10]. 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[11]. 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.

References

1 Slater, T., Lawrence, I.R., Otosaka, I.N., Shepherd, A., Gourmelen, N., Jakob, L., Tepes, P., Gilbert, L. and Nienow, P., 2021. Earth’s ice imbalance. The Cryosphere15(1), pp.233-246.

2 Hugonnet, R., McNabb, R., Berthier, E., Menounos, B., Nuth, C., Girod, L., Farinotti, D., Huss, M., Dussaillant, I., Brun, F. and Kääb, A., 2021. Accelerated global glacier mass loss in the early twenty-first century. Nature592(7856), pp.726-731.

3 Mouginot, J., Rignot, E., and Scheuchl, B.: Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013, Geophys. Res. Lett., 41, 1576–1584, https://doi.org/10.1002/2013GL059069, 2014. 

4 Hogg, A. E., Shepherd, A., Cornford, S. L., Briggs, K. H., Gourmelen, N., Graham, J. A., Joughin, I., Mouginot, J., Nagler, T., Payne, A. J., Rignot, E., and Wuite, J.: Increased ice flow in Western Palmer Land linked to ocean melting, Geophys. Res. Lett., 44, 4159–4167, https://doi.org/10.1002/2016GL072110, 2017. 

5 Enderlin, E. M., Howat, I. M., Jeong, S., Noh, M.-J., van Angelen, J. H., and van den Broeke, M. R.: An improved mass budget for the Greenland ice sheet, Geophys. Res. Lett., 41, 866–872, https://doi.org/10.1002/2013GL059010, 2014. 

6 Bevis, M., Harig, C., Khan, S. A., Brown, A., Simons, F. J., Willis, M., Fettweis, X., Broeke, M. R. van den, Madsen, F. B., Kendrick, E., Caccamise, D. J., Dam, T. van, Knudsen, P., and Nylen, T.: Accelerating changes in ice mass within Greenland, and the ice sheet’s sensitivity to atmospheric forcing, P. Natl. Acad. Sci., 116, 1934–1939, https://doi.org/10.1073/pnas.1806562116, 2019. 

7  The IMBIE Team: Mass balance of the Greenland Ice Sheet from 1992 to 2018, Nature, 579, 233–239, https://doi.org/10.1038/s41586-019-1855-2, 2020 (data available at: http://imbie.org/data-downloads/). 

8 Edwards, T.L., Nowicki, S., Marzeion, B., Hock, R., Goelzer, H., Seroussi, H., Jourdain, N.C., Slater, D.A., Turner, F.E., Smith, C.J. and McKenna, C.M., 2021. Projected land ice contributions to twenty-first-century sea level rise. Nature593(7857), pp.74-82.

9  Edwards, T., 2017. Current and future impacts of sea level rise on the UK. Foresight–future of the sea evidence review. Government office for science, UK.

10 Howard, T., Lowe, J. and Horsburgh, K., 2010. Interpreting century-scale changes in southern North Sea storm surge climate derived from coupled model simulations. Journal of Climate23(23), pp.6234-6247.

11 Pace, S., 2021. Urban infrastructure inundation risk from permanent sea-level rise scenarios in London (UK), Bangkok (Thailand) and Mumbai (India): A comparative analysis. Master Thesis in Geographical Information Science.

Polar Pride 2021

RHUL’s Geography department hosted their first polar pride event yesterday (18/11/21) hosted by Bethan Davies. The event brought together staff and students to celebrate TLGBQAI+ polar scientists, where we enjoyed cake and discussed the importance of polar pride through a Q&A with PhD students Dan Parkes and Laura Boyall.

The first polar pride took place in 2018 and demonstrated a commitment to supporting and enhancing diversity in polar science. Pride flags have been flown across the polar regions this year to celebrate polar pride worldwide.

Dan Parkes, Laura Boyall and Bethan Davies at RHUL Geography’s polar pride event.