Impacts of glacier retreat

The continued retreat of glaciers will have a number of different quantitative impacts. In areas that are heavily dependent on water runoff from glaciers that melt during the warmer summer months, a continuation of the current retreat will eventually deplete the glacial ice and substantially reduce or eliminate runoff. A reduction in runoff will affect the ability to irrigate crops and will reduce summer stream flows necessary to keep dams and reservoirs replenished. This situation is particularly acute for irrigation in South America, where numerous artificial lakes are filled almost exclusively by glacial melt.Central Asian countries have also been historically dependent on the seasonal glacier melt water for irrigation and drinking supplies. In Norway, the Alps, and the Pacific Northwest of North America, glacier runoff is important for hydropower.
Some of this retreat has resulted in efforts to slow down the loss of glaciers in the Alps. To retard melting of the glaciers used by certain Austrian ski resorts, portions of the Stubai and Pitztal Glaciers were covered with plastic. In Switzerland plastic sheeting is also used to reduce the melt of glacial ice used as ski slopes.While covering glaciers with plastic sheeting may prove advantageous to ski resorts on a small scale, this practice is not expected to be economically practical on a much larger scale.
Many species of freshwater and saltwater plants and animals are dependent on glacier-fed waters to ensure the cold water habitat to which they have adapted. Some species of freshwater fish need cold water to survive and to reproduce, and this is especially true with salmon and cutthroat trout. Reduced glacial runoff can lead to insufficient stream flow to allow these species to thrive. Alterations to the ocean currents, due to increased freshwater inputs from glacier melt, and the potential alterations to thermohaline circulation of the worlds oceans, may impact existing fisheries upon which humans depend as well.
The potential for major sea level rise depends mostly on a significant melting of the polar ice caps of Greenland and Antarctica, as this is where the vast majority of glacial ice is located. The British Antarctic Survey has determined from climate modeling that for at least the next 50 years, snowfall on the continent of Antarctica should continue to exceed glacial losses from global warming. The amount of glacial loss on the continent of Antarctica is not increasing significantly, and it is not known if the continent will experience a warming or a cooling trend, although the Antarctic Peninsula has warmed in recent years, causing glacier retreat in that region.If all the ice on the polar ice caps were to melt away, the oceans of the world would rise an estimated 70 m (230 ft). However, with little major melt expected in Antarctica, sea level rise of not more than 0.5 m (1.6 ft) is expected through the 21st century, with an average annual rise of 0.004 m (0.013 ft) per year. Thermal expansion of the world's oceans will contribute, independent of glacial melt, enough to double those figures

Thermohaline circulation

The thermohaline circulation (THC) is the global density-driven circulation of the oceans. Derivation is from thermo- for heat and -haline for salt, which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) head polewards from the equatorial Atlantic Ocean, cooling all the while and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1600 years) upwell in the North Pacific . Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's ocean a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.
The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyer, the global conveyor belt, or, most commonly, the meridional overturning circulation

Movement of thermohaline circulation

Formation and movement of the deep water masses at North Atlantic Ocean, creates sinking water masses that fills the basin and flows very slowly into the deep abyssal plains of the Atlantic. This high latitude cooling and the low latitude heating drives the movement of the deep water a polar southward flow. The deep water flows through Antarctic Ocean Basin around South Africa where it is split into two routes: one into the Indian Ocean and one past Australia into the Pacific.
At the Indian Ocean, some of the cold and salty water from Atlantic -- drawn by the flow of warmer and fresher upper ocean water from the tropical Pacific -- causes a vertical exchange of dense, sinking water with lighter water below. It is known as overturning. In the Pacific Ocean, the rest of the cold and salty water from the Atlantic undergoes Haline forcing and slowly becomes warmer and fresher.
The out-flowing undersea of cold and salty water makes the sea level of the Atlantic slightly lower than the Pacific and salinity or halinity of water at the Atlantic higher than the Pacific. This generates a large but slow flow of warmer and fresher upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelago to replace the cold and salty Antarctic Bottom Water. This is also known as Haline forcing (net high latitude freshwater gain and low latitude evaporation). This warmer, fresher water from the Pacific flows up through the South Atlantic to Greenland, where it cools off and undergoes evaporative cooling and sinks to the ocean floor, providing a continuous thermohaline circulation.
Hence, a recent and popular name for the thermohaline circulation, emphasizing the vertical nature and pole-to-pole character of this kind of ocean circulation, is the meridional overturning circulation.
The deep water masses that participate in the MOC have chemical, temperature and isotopic ratio signatures and can be traced, their flow rate calculated, and their age determined.

Tephrochronology

Tephrochronology is a geochronological technique that utilises discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which palaeoenvironmental or archaeological records can be placed. Such an established event provides a "tephra horizon". Each volcanic event has a unique chemical 'fingerprint' that is identifiable in its fallout.
The main advantages of the technique are that the volcanic ash layers can be relatively easily identified in many sediments and that the tephra layers are deposited relatively instantaneously over a wide spatial area. This means they provide accurate temporal marker layers which can be used to verify or corroborate other dating techniques, linking sequences widely separated by location into a unified chronology that correlates climactic sequences and events.
The problems associated with tephochronology are that its use has been limited to areas of frequent large-scale volcanic activity and that tephra chemistry can become altered over time. It also requires accurate geochemical fingerprinting (usually via an electron microprobe) and radiometric dating of proximal tephra deposits.
Early tephra horizons were identified with the Saksunarvatn tephra (Icelandic origin, ca 10.2 cal. ka BP), forming a horizon in the late Pre-Boreal of Northern Europe, the Vedde ash (also Icelandic in origin, ca 12.0 cal. ka BP) and the Laacher See tephra (in the Eifel volcanic field, ca 12.9 cal. ka BP). Major volcanoes which have been used in tephrochronological studies include Vesuvius, Hekla and Santorini. Minor volcanic events may also leave their fingerprint in the geological record: Hayes Volcano is responsible for a series of six major tephra layers in the Cook Inlet region of Alaska. Tephra horizons provide a synchronous check against which to correlate the palaeoclimatic reconstructions that are obtained from terrestrial records, like fossil pollen studies (palynology), from varves in lake sediments or from marine deposits and ice-core records, and to extend the limitations of carbon-14 dating.
A pioneer in the use of tephra layers as marker horizons to establish chronology was Sigurdur Thorarinsson, who began by studying the layers he found in his native Iceland. Since the late 1990s, techniques developed by Chris S. M. Turney (QUB, Belfast) and others for extracting tephra horizons invisible to the naked eye ("cryptotephra") have revolutionised the application of tephrochronology. This technique relies upon the difference between the specific gravity of the microtephra shards and the host sediment matrix. It has led to the first discovery of the Vedde ash on the mainland of Britain, in Sweden, in the Netherlands, in the Swiss Lake Soppensee and in two sites on the Karelian Isthmus of Baltic Russia. It has also revealed previously undetected ash layers, such as the hitherto unrecorded Borrobol Tephra, dated to ca. 14,400 years BP calibrated (Wastegård 2004).

Examples of climate change

Climate change has continued throughout the entire history of Earth. The field of paleoclimatology has provided information of climate change in the ancient past, supplementing modern observations of climate.
Climate of the deep past
Faint young sun paradox
Snowball earth
Oxygen Catastrophe
Climate of the last 500 million years
Phanerozoic overview
Paleocene–Eocene Thermal Maximum
Cretaceous Thermal Maximum
Permo–Carboniferous Glaciation
Ice ages
Climate of recent glaciations
Dansgaard–Oeschger event
Younger Dryas
Ice age temperatures
Recent climate
Holocene Climatic Optimum
Medieval Warm Period
Little Ice Age
Year Without a Summer
Temperature record of the past 1000 years
Global warming
Hardiness Zone Migration

Climate change and biodiversity

The life cycles of many wild plants and animals are closely linked to the passing of the seasons; climatic changes can lead to interdependent pairs of species (e.g. a wild flower and its pollinating insect) losing synchronization, if, for example, one has a cycle dependent on day length and the other on temperature or precipitation. In principle, at least, this could lead to extinctions or changes in the distribution and abundance of species. One phenomenon is the movement of species northwards in Europe. A recent study by Butterfly Conservation in the UK, has shown that relatively common species with a southerly distribution have moved north, whilst scarce upland species have become rarer and lost territory towards the south. This picture has been mirrored across several invertebrate groups. Drier summers could lead to more periods of drought, potentially affecting many species of animal and plant. For example, in the UK during the drought year of 2006 significant numbers of trees died or showed dieback on light sandy soils. In Australia, since the early 90s, tens of thousands of flying foxes (Pteropus) have died as a direct result of extreme heat. Wetter, milder winters might affect temperate mammals or insects by preventing them hibernating or entering torpor during periods when food is scarce. One predicted change is the ascendancy of 'weedy' or opportunistic species at the expense of scarcer species with narrower or more specialized ecological requirements. One example could be the expanses of bluebell seen in many woodlands in the UK. These have an early growing and flowering season before competing weeds can develop and the tree canopy closes. Milder winters can allow weeds to overwinter as adult plants or germinate sooner, whilst trees leaf earlier, reducing the length of the window for bluebells to complete their life cycle. Organisations such as Wildlife Trust, World Wide Fund for Nature, Birdlife International and the Audubon Society are actively monitoring and research the effects of climate change on biodiversity and advance policies in areas such as landscape scale conservation to promote adaptation to climate change.