Increasing cryospheric hazards in a warming climate

Highlights

• The cryosphere components have been shrinking due to climate warming.

• Hazards from atmospheric cryosphere decreased, while future changes are unknown.

• Sea ice extent and icebergs are declining, but their risks remain unchanged.

• The hazards from glacier, permafrost will increase in the future.

• Prediction, monitoring and warning of cryospheric hazards are important.

Abstract

The cryosphere is an important component of the global climate system. Cryospheric components are sensitive to climate warming, and changes in the cryosphere can lead to serious hazards to human society, while the comprehensive understanding of cryospheric hazards largely remains unknown. Here we summarized the hazards related to atmospheric, oceanic and land cryosphere. The different types of cryospheric hazards, including their phenomena, mechanisms and impacts were reviewed. Our results suggested that: 1) The recorded hazards from atmospheric cryosphere including frost, hail, freezing rain decreased or showed great spatial heterogeneities, while their future changes are difficult to predict, and the extreme cold events in winter may increase in the future; 2) Sea ice extent declines rapidly, and iceberg numbers will increase. The permafrost-dominated coastline erosion will be exacerbated by climate warming. Meanwhile, the sea level rise is expected to continue in the next decades; 3) The glacier collapse, glacial lake outbursts and paraglacial readjustments will increase in the future. Although the total area of snow cover will decrease, the heavy snow events, snow avalanches, and snowmelt floods will not decrease simultaneously. The permafrost-related rock and debris flow and thaw slump will also increase with permafrost degradation. Taken together, we concluded the cryosphere is shrinking, while cryospheric hazards will likely increase in a warming climate.

Introduction

The term cryosphere is derived “kryos”, is a term for the portions of the earth's surface where water is in solid form, while the definition can be expanded to earth layers with low temperatures and all the ice in the air, land and ocean (Barry and Gan, 2011). From this definition, all the snow cover, glaciers, ice shelves, ice sheets, sea ice, icebergs, lake ice, river ice, frozen ground, small ice caps and ice in clouds, frozen drops, graupel, hail, and frost are all belonged to the components of the cryosphere. In a narrow sense, the cryosphere mainly refers the glaciers (Rignot et al., 2013; Vasskog et al., 2015; Zemp et al., 2019), permafrost (Obu et al., 2019), snow cover (Bormann et al., 2018; Xu et al., 2016), and sea ice (Parkinson, 2014; Parkinson and DiGirolamo, 2016) because these components are continuously distributed below the freezing point with a certain thickness. These components account for 12% (in August)-14% (January) of the earth's surface (Barry and Gan, 2011; IPCC, 2019; Ohmura, 2004).

As a product of cold climate, the cryosphere is very sensitive to global warming. During the past 50 years, the high-latitude and high-altitude regions, where the cryosphere mainly occurs, have been experienced 2–3 times temperature increasing than the global average (Taylor et al., 2013). Consequently, the cryosphere has been subjected to dramatic change, i.e., ice sheets melting (Cazenave, 2006; Chen et al., 2006; Feldmann and Levermann, 2015; Rignot et al., 2019; Rogozhina et al., 2016), glaciers retreating (Li et al., 2019; Oerlemans, 2005; Roe et al., 2017; Shakun et al., 2015), permafrost degradation (Biskaborn et al., 2019; Jorgenson et al., 2001; Plaza et al., 2019), snow cover extent decreasing (Derksen and Brown, 2012; Hori et al., 2017; Rizzi et al., 2018; Yeo et al., 2017). These changes can create feedback to climate because the cryosphere not only affects the global energy balance, its dynamics can affect the global air and ocean circulation (Olsen et al., 2011; Schmittner et al., 2002). In addition, the cryosphere contains a large amount of organic matter, and the decomposition of the organic matter along with the cryosphere shrinkage potentially release greenhouse gases into the air and further create a positive feedback to climate warming (Hugelius et al., 2013; Schuur et al., 2015; Zhao et al., 2018). Therefore, understanding the changes and consequences of the cryosphere has become a critical step toward developing human adaptation strategies in a warming world.

The formation and melting of the ice indicate phase changes of water. For the ice in the air, the appearance of solid water can cause great damage to human society. For the ice in the ocean and land, the melting of ice can produce liquid water and remove the support system for the upper ice or soil layer (Joughin et al., 2014; Kääb et al., 2018; Kokelj and Jorgenson, 2013; Qin et al., 2018). These processes can lead to the destabilization of cryospheric environments, including ice shelf (Feldmann and Levermann, 2015; Hogg and Gudmundsson, 2017; Ingels et al., 2021; Martin et al., 2019; Robel and Banwell, 2019) and glacier collapse (Deline et al., 2015; Falaschi et al., 2019; Paul, 2019; Tian et al., 2017), rock and ice avalanche (Chiarle et al., 2007; Dufresne et al., 2019; Dunning et al., 2015; Schaub et al., 2016), glacier and snow melting flood (Brown et al., 2014; Duan et al., 2020; Janský et al., 2010; Sikorska et al., 2015), glacial lake outburst (Bajracharya and Mool, 2009; Ding and Liu, 1992; Harrison et al., 2018; Schwanghart et al., 2016; Shangguan et al., 2017; Veh et al., 2019), and thermokarst development (Farquharson et al., 2019; Mu et al., 2020b; Nelson et al., 2002; Saito et al., 2018; Turetsky et al., 2020). These phenomena are closely associated with the processes of the cryosphere, and thus are called cryospheric hazards. Although cryospheric hazards attracted many pubic attentions due to the risk of loss of life and the threat to costly infrastructures (Haeberli and Whiteman, 2015; Mark et al., 2017; Motschmann et al., 2020; Richardson and Reynolds, 2000), there is still no synthetic review for the changes of cryospheric hazards in the past decades. In this review, we presented the main cryospheric hazards and their frequencies. We also discussed the risks of cryospheric hazards and their possible future trends. Finally, we summarized the approaches for the mitigation of these hazards in the future.