2. Glacier monitoring and projects implemented in the Arctic

#### 2.1. Cryosphere

Cryosphere refers to "the part of the Earth's crust and atmosphere subject to temperatures below 0C for at least part of each year" [4]. The snow, ice, and frozen ground all constitute the cryosphere, considered a source of climatic diagnosis due to its sensitivity to air temperature and precipitation changes. The most recent intergovernmental panel on climate change (IPCC) assessment [5] emphasizes also the importance of cryosphere in the Earth's ecosystem as a reservoir of solidified water. Glaciers and the great ice sheets of Greenland or Antarctica are only part of the cryosphere, as shown in Figure 1.

Figure 1. Division of the cryosphere and its components: <sup>1</sup> Global land surface: 147.6 Mkm<sup>2</sup> , 2 Global ocean area: 362.5 Mkm<sup>2</sup> [5].

The global land surface covered by glaciers (0.5%) is the least abundant cryosphere component. It is referred to as "ice on land." Nevertheless, the general significance of glaciers for the sea level equivalent (0.41 m a.s.l.) is the highest among the components, except for ice sheets (Antarctic: 58.3 m, Greenland: 7.36 m). Glaciers are long-term components of the cryosphere, with a lifespan exceeding freshwater ice on rivers and lakes (seasonal) and sea ice (several years in the Arctic), but shorter than ice sheets and permafrost, surviving even millions of years [5] (Table 1).

Considering their contribution to the sea-level rise and the lifespan of particular components of the cryosphere, glaciers are of extreme significance for the environment as an indicator of climate change in the context of global warming.
