Climate change

Global surface temperatures increased by 0.8°C on average during the 20^th century and twice as much in the Arctic and sub-polar areas. This warming does not appear that large considering day-to-day temperature fluctuations, but as a change in mean annual temperature it has substantial consequences, resulting for example in melting of sea-ice and glaciers, rising sea levels, enhanced vegetation growth in temperate regions and changes in migratory routes of birds and animals.

The main cause of the current global warming is anthropogenic emission of carbon dioxide (CO₂) and other greenhouse gases, such as methane (CH₄), into the atmosphere. The increase in the concentration of greenhouse gases is due to combustion of fossil fuels, such as coal and oil, in electric power plants, transportation and industry, and a decrease in the uptake of CO₂ due to deforestation, soil erosion and agriculture. Carbon dioxide levels in the atmosphere have increased by more than 45% since the industrial revolution. The oceans have absorbed one third of anthropogenic CO₂ emissions since then leading to acidification, which inhibits shell growth. Ocean acidification will eventually lead to marine species extinctions and have widespread effects on marine ecosystems.

Ten key climate indicators that all point to a warming world. Source: Parry et al. (2007).

Glaciers

Glaciers are the largest freshwater reservoir on Earth. The largest glaciers are the ice sheets in Antarctica and Greenland. Many smaller glaciers are found in the polar and subpolar areas and actually in mountain regions on every continent. Glacial meltwater is used for irrigation of crops, as drinking water for millions of people and for the generation of electricity by hydropower plants.

Icelandic glaciers contain 3500 km³ of ice, whereof the Vatnajökull ice cap alone holds 3000 km³. If all Icelandic glaciers would melt, they could submerge the entire country below 30 m of water, or raise global sea level by one cm. However, if all the glaciers of the world were to melt, sea level would rise by about 65 m. Coastal cities would be submerged as well as large parts of the Earth’s agricultural land.

Icelandic glaciers have retreated rapidly for more than two decades and glacier downwasting is one of the most obvious consequences of the warming climate. Several glaciers have disappeared in the last decade, such as Ok glacier in W-Iceland. Glaciers in Iceland reached their maximum size at the end of the 19^th century and have since retreated and lost more than 2100 km² (17%) of their area. Runoff from the glaciers has changed, and glacial lakes have formed or increased in size in front of many of them, while some have disappeared. The rate of retreat has increased in the last couple of decades and during the period 2000–2017 the glaciers lost more than 700 km² of their area which amounts to 43 km² per year on average (for comparison the area of Reykjavík is 273 km²).

Map of the glaciers of the world. Source: British Geological Survey.

Coastlines of Europe of all glaciers were to melt. Source: National Geographic. 

Vatnajökull National Park

Within Vatnajökull National Park, many landscape forms bear witness to the downwasting of glaciers, which is one of the most obvious consequence of anthropogenic climate warming. At present, all the southern outlet glaciers of Vatnajökull are retreating and thinning at unprecedented rates. These glaciers reached their maximum Holocene (the last 10 000 years) size only 130 years ago, as evidenced by glacial geomorphological forms, including well preserved lateral moraines and end moraines. Some of the glaciers in the park are analogues to the glacial enviroments of the vast ice sheets of Greenland and Antarctica, and the periglacial environments parallel to the conditions at the ice margins of the continental ice sheets of the Quaternary period.

Heinabergsjökull outlet glacier and the terminal lake which has increased in size in recent years. Photo: Þorvarður Árnason, 2018.

Skálafellsjökull (closer) and Heinabergsjökull outlet glaciers, the glacier moraines from ca 1890 are visible in the foreground, which have partly been washed away in repeated jökulhlaups from ice-dammed lakes at the beginning of the 20th century. Photo: Snævarr Guðmundsson, 2006.

The snout of Hrútárjökull, Fjallsárjökull and Breiðamerkurjökull outlet glaciers in the background. The Little Ice Age moraines from ca 1890 are visible in the moss covered sandur plain. Terminal glacial lakes have increased in size in recent decades and enhance ablation. Photo: Snævarr Guðmundsson, 2006.

The terminus of Fláajökull outlet glacier, which has lowered by 250 m in the last 130 years. Photo: Þorvarður Árnason, 2016.