Misplaced Pages

#808191

77-597: In general, climate models show a 1.5-2 °C drop in Antarctica and other temperate regions where glacial readvances are typically evident. Climate continued to warm after 13,000 years BP and glaciers showed signs of abrupt withdrawal from their respective ACR aged moraines . The mechanisms behind the atmospheric and oceanic reorganization are still debated, although strengthening of the Atlantic Meridional Overturnig Circulation

154-475: A shear zone , a marginal ice zone and a central pack . Drift ice consists of floes , individual pieces of sea ice 20 metres (66 ft) or more across. There are names for various floe sizes: small – 20 to 100 m (66 to 328 ft); medium – 100 to 500 m (330 to 1,640 ft); big – 500 to 2,000 m (1,600 to 6,600 ft); vast – 2 to 10 kilometres (1.2 to 6.2 mi); and giant – more than 10 km (6.2 mi). The term pack ice

231-430: A beach with a light swell, ice eggs up to the size of a football can be created. Nilas designates a sea ice crust up to 10 centimetres (3.9 in) in thickness. It bends without breaking around waves and swells. Nilas can be further subdivided into dark nilas – up to 5 cm (2.0 in) in thickness and very dark and light nilas – over 5 cm (2.0 in) in thickness and lighter in color. Young ice

308-445: A certain point such a disc shape becomes unstable and the growing isolated crystals take on a hexagonal, stellar form, with long fragile arms stretching out over the surface. These crystals also have their c-axis vertical. The dendritic arms are very fragile and soon break off, leaving a mixture of discs and arm fragments. With any kind of turbulence in the water, these fragments break up further into random-shaped small crystals which form

385-413: A common software infrastructure shared by all U.S. climate researchers, and holding an annual climate modeling forum, the report found. Cloud-resolving climate models are nowadays run on high intensity super-computers which have a high power consumption and thus cause CO 2 emissions.  They require exascale computing (billion billion – i.e., a quintillion – calculations per second). For example,

462-419: A day; the ocean is MOM-3 ( Modular Ocean Model ) with a 3.75° × 3.75° grid and 24 vertical levels. Box models are simplified versions of complex systems, reducing them to boxes (or reservoirs ) linked by fluxes. The boxes are assumed to be mixed homogeneously. Within a given box, the concentration of any chemical species is therefore uniform. However, the abundance of a species within a given box may vary as

539-405: A function of elevation (i.e. relative humidity distribution). This has been shown by refining the zero dimension model in the vertical to a one-dimensional radiative-convective model which considers two processes of energy transport: Radiative-convective models have advantages over simpler models and also lay a foundation for more complex models. They can estimate both surface temperature and

616-573: A function of time due to the input to (or loss from) the box or due to the production, consumption or decay of this species within the box. Simple box models, i.e. box model with a small number of boxes whose properties (e.g. their volume) do not change with time, are often useful to derive analytical formulas describing the dynamics and steady-state abundance of a species. More complex box models are usually solved using numerical techniques. Box models are used extensively to model environmental systems or ecosystems and in studies of ocean circulation and

693-569: A much more reliable measure of long-term changes in sea ice. In comparison to the extended record, the sea-ice extent in the polar region by September 2007 was only half the recorded mass that had been estimated to exist within the 1950–1970 period. Arctic sea ice extent ice hit an all-time low in September 2012, when the ice was determined to cover only 24% of the Arctic Ocean, offsetting the previous low of 29% in 2007. Predictions of when

770-633: A process called congelation growth. This growth process yields first-year ice. In rough water, fresh sea ice is formed by the cooling of the ocean as heat is lost into the atmosphere. The uppermost layer of the ocean is supercooled to slightly below the freezing point, at which time tiny ice platelets (frazil ice) form. With time, this process leads to a mushy surface layer, known as grease ice . Frazil ice formation may also be started by snowfall , rather than supercooling. Waves and wind then act to compress these ice particles into larger plates, of several meters in diameter, called pancake ice . These float on

847-565: A robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases." The World Climate Research Programme (WCRP), hosted by the World Meteorological Organization (WMO), coordinates research activities on climate modelling worldwide. A 2012 U.S. National Research Council report discussed how the large and diverse U.S. climate modeling enterprise could evolve to become more unified. Efficiencies could be gained by developing

SECTION 10

#1732769140809

924-479: A standard protocol for studying the output of coupled atmosphere-ocean general circulation models. The coupling takes place at the atmosphere-ocean interface where the sea ice may occur. In addition to global modeling, various regional models deal with sea ice. Regional models are employed for seasonal forecasting experiments and for process studies . Sea ice is part of the Earth's biosphere . When sea water freezes,

1001-442: A state of shear . Sea ice deformation results from the interaction between ice floes, as they are driven against each other. The result may be of three types of features: 1) Rafted ice , when one piece is overriding another; 2) Pressure ridges , a line of broken ice forced downward (to make up the keel ) and upward (to make the sail ); and 3) Hummock , a hillock of broken ice that forms an uneven surface. A shear ridge

1078-421: A suspension of increasing density in the surface water, an ice type called frazil or grease ice . In quiet conditions the frazil crystals soon freeze together to form a continuous thin sheet of young ice; in its early stages, when it is still transparent – that is the ice called nilas . Once nilas has formed, a quite different growth process occurs, in which water freezes on to the bottom of the existing ice sheet,

1155-553: A swath of records that show a millennial-scale climate cooling during the ACR. Stratigraphic records from the Southern Alps track glacier advances and pronounced forest changes between 14,500 and 12,800 years BP. Chironomid-inferred temperature records suggest a summer temperature decrease of ~3-2 °C. Paleoclimatic records from Tasmania have bracketed a local climate cooling event between 14,900 and 12,800 years BP, coincident with

1232-413: Is where The constant parameters include The constant π r 2 {\displaystyle \pi \,r^{2}} can be factored out, giving a nildimensional equation for the equilibrium where The remaining variable parameters which are specific to the planet include This very simple model is quite instructive. For example, it shows the temperature sensitivity to changes in

1309-422: Is a general term used for recently frozen sea water that does not yet make up solid ice. It may consist of frazil ice (plates or spicules of ice suspended in water), slush (water saturated snow), or shuga (spongy white ice lumps a few centimeters across). Other terms, such as grease ice and pancake ice , are used for ice crystal accumulations under the action of wind and waves. When sea ice begins to form on

1386-464: Is a pressure ridge that formed under shear – it tends to be more linear than a ridge induced only by compression. A new ridge is a recent feature – it is sharp-crested, with its side sloping at an angle exceeding 40 degrees. In contrast, a weathered ridge is one with a rounded crest and with sides sloping at less than 40 degrees. Stamukhi are yet another type of pile-up but these are grounded and are therefore relatively stationary. They result from

1463-447: Is a significant source of errors in sea-ice thickness retrieval using radar and laser satellite altimetry, resulting in uncertainties of 0.3–0.4 m. Changes in sea ice conditions are best demonstrated by the rate of melting over time. A composite record of Arctic ice demonstrates that the floes' retreat began around 1900, experiencing more rapid melting beginning within the past 50 years. Satellite study of sea ice began in 1979 and became

1540-465: Is a transition stage between nilas and first-year ice and ranges in thickness from 10 cm (3.9 in) to 30 cm (12 in), Young ice can be further subdivided into grey ice – 10 cm (3.9 in) to 15 cm (5.9 in) in thickness and grey-white ice – 15 cm (5.9 in) to 30 cm (12 in) in thickness. Young ice is not as flexible as nilas, but tends to break under wave action. Under compression, it will either raft (at

1617-630: Is a type of climate model. It employs a mathematical model of the general circulation of a planetary atmosphere or ocean. It uses the Navier–Stokes equations on a rotating sphere with thermodynamic terms for various energy sources ( radiation , latent heat ). These equations are the basis for computer programs used to simulate the Earth's atmosphere or oceans. Atmospheric and oceanic GCMs (AGCM and OGCM ) are key components along with sea ice and land-surface components. GCMs and global climate models are used for weather forecasting , understanding

SECTION 20

#1732769140809

1694-482: Is alluded to in general. Global climate during the last Ice Age reached its coolest temperatures between c. 21,000 and 18,000 years BP, marking the onset of the last glacial termination. This transition out of the last Ice Age , also known as deglaciation , lasted until c. 11,500 years BP, when temperature, atmospheric CO 2 concentrations, and sea level ceased to increase as rapidly, and glaciers reached their less extensive Holocene positions. The period bracketed as

1771-459: Is attached (or frozen) to the shoreline (or between shoals or to grounded icebergs ). If attached, it is called landfast ice, or more often, fast ice (as in fastened ). Alternatively and unlike fast ice, drift ice occurs further offshore in very wide areas and encompasses ice that is free to move with currents and winds. The physical boundary between fast ice and drift ice is the fast ice boundary . The drift ice zone may be further divided into

1848-542: Is considerable confidence that climate models provide credible quantitative estimates of future climate change, particularly at continental scales and above. This confidence comes from the foundation of the models in accepted physical principles and from their ability to reproduce observed features of current climate and past climate changes. Confidence in model estimates is higher for some climate variables (e.g., temperature) than for others (e.g., precipitation). Over several decades of development, models have consistently provided

1925-585: Is particularly common around Antarctica . Russian scientist Vladimir Vize (1886–1954) devoted his life to study the Arctic ice pack and developed the Scientific Prediction of Ice Conditions Theory , for which he was widely acclaimed in academic circles. He applied this theory in the field in the Kara Sea , which led to the discovery of Vize Island . The annual freeze and melt cycle is set by

2002-401: Is sea ice that has survived at least one melting season ( i.e. one summer). For this reason, this ice is generally thicker than first-year sea ice. Old ice is commonly divided into two types: second-year ice , which has survived one melting season and multiyear ice , which has survived more than one. (In some sources, old ice is more than two years old.) Multi-year ice is much more common in

2079-400: Is still useful in that the laws of physics are applicable in a bulk fashion to unknown objects, or in an appropriate lumped manner if some major properties of the object are known. For example, astronomers know that most planets in our own solar system feature some kind of solid/liquid surface surrounded by a gaseous atmosphere. A very simple model of the radiative equilibrium of the Earth

2156-518: Is the main driving force, along with ocean currents. The Coriolis force and sea ice surface tilt have also been invoked. These driving forces induce a state of stress within the drift ice zone. An ice floe converging toward another and pushing against it will generate a state of compression at the boundary between both. The ice cover may also undergo a state of tension , resulting in divergence and fissure opening. If two floes drift sideways past each other while remaining in contact, this will create

2233-426: Is used either as a synonym to drift ice , or to designate drift ice zone in which the floes are densely packed. The overall sea ice cover is termed the ice canopy from the perspective of submarine navigation. Another classification used by scientists to describe sea ice is based on age, that is, on its development stages. These stages are: new ice , nilas , young ice , first-year and old . New ice

2310-637: The Antarctic ice pack of the Southern Ocean . Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology , including the ocean's ecosystems . Due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs , which are chunks of ice shelves or glaciers that calve into

2387-502: The Arctic than it is in the Antarctic . The thickness of old sea ice typically ranges from 2 to 4 m. The reason for this is that sea ice in the south drifts into warmer waters where it melts. In the Arctic, much of the sea ice is land-locked. While fast ice is relatively stable (because it is attached to the shoreline or the seabed), drift (or pack) ice undergoes relatively complex deformation processes that ultimately give rise to sea ice's typically wide variety of landscapes. Wind

Antarctic Cold Reversal - Misplaced Pages Continue

2464-549: The Frontier exascale supercomputer consumes 29 MW. It can simulate a year’s worth of climate at cloud resolving scales in a day. Techniques that could lead to energy savings, include for example: "reducing floating point precision computation; developing machine learning algorithms to avoid unnecessary computations; and creating a new generation of scalable numerical algorithms that would enable higher throughput in terms of simulated years per wall clock day." Climate models on

2541-595: The NOAA Geophysical Fluid Dynamics Laboratory AOGCMs represent the pinnacle of complexity in climate models and internalise as many processes as possible. However, they are still under development and uncertainties remain. They may be coupled to models of other processes, such as the carbon cycle , so as to better model feedback effects. Such integrated multi-system models are sometimes referred to as either "earth system models" or "global climate models." Simulation of

2618-542: The carbon cycle . They are instances of a multi-compartment model . In 1961 Henry Stommel was the first to use a simple 2-box model to study factors that influence ocean circulation. In 1956, Norman Phillips developed a mathematical model that realistically depicted monthly and seasonal patterns in the troposphere. This was the first successful climate model. Several groups then began working to create general circulation models . The first general circulation climate model combined oceanic and atmospheric processes and

2695-407: The climate , and forecasting climate change . Atmospheric GCMs (AGCMs) model the atmosphere and impose sea surface temperatures as boundary conditions. Coupled atmosphere-ocean GCMs (AOGCMs, e.g. HadCM3 , EdGCM , GFDL CM2.X , ARPEGE-Climat) combine the two models. The first general circulation climate model that combined both oceanic and atmospheric processes was developed in the late 1960s at

2772-529: The ice dynamics and the thermodynamical properties (see Sea ice emissivity modelling , Sea ice growth processes and Sea ice thickness ). There are many sea ice model computer codes available for doing this, including the CICE numerical suite . Many global climate models (GCMs) have sea ice implemented in their numerical simulation scheme in order to capture the ice–albedo feedback correctly. Examples include: The Coupled Model Intercomparison Project offers

2849-448: The ocean surface and collide with one another, forming upturned edges. In time, the pancake ice plates may themselves be rafted over one another or frozen together into a more solid ice cover, known as consolidated pancake ice. Such ice has a very rough appearance on top and bottom. If sufficient snow falls on sea ice to depress the freeboard below sea level, sea water will flow in and a layer of ice will form of mixed snow/sea water. This

2926-424: The ACR (14,700-13,000 years BP) is characterized by a reversal or halt in these deglacial trends, i.e., temperatures cooled, atmospheric CO 2 concentrations halted, and glaciers readvanced. Climatic, geologic, and ecologic changes during the ACR are nuanced among geographical regions that showed signs of cooling. The ACR is characterized in Antarctica through the ice cores retrieved from locations spread across

3003-481: The ACR. A paucity in local fire events and an increase in cold-tolerant Rainforest taxa attest to this climatic cooling in Tasmania. Climate model Numerical climate models (or climate system models ) are mathematical models that can simulate the interactions of important drivers of climate . These drivers are the atmosphere , oceans , land surface and ice . Scientists use climate models to study

3080-448: The Earth's temperature gets warmer. Furthermore, the sea ice itself functions to help keep polar climates cool, since the ice exists in expansive enough amounts to maintain a cold environment. At this, sea ice's relationship with global warming is cyclical; the ice helps to maintain cool climates, but as the global temperature increases, the ice melts and is less effective in keeping those climates cold. The bright, shiny surface ( albedo ) of

3157-566: The Sun is in the form of short wave electromagnetic radiation , chiefly visible and short-wave (near) infrared . The outgoing energy is in the form of long wave (far) infrared electromagnetic energy. These processes are part of the greenhouse effect . Climate models vary in complexity. For example, a simple radiant heat transfer model treats the Earth as a single point and averages outgoing energy. This can be expanded vertically (radiative-convective models) and horizontally. More complex models are

Antarctic Cold Reversal - Misplaced Pages Continue

3234-435: The amount of melting ice. Though the size of the ice floes is affected by the seasons, even a small change in global temperature can greatly affect the amount of sea ice and due to the shrinking reflective surface that keeps the ocean cool, this sparks a cycle of ice shrinking and temperatures warming. As a result, the polar regions are the most susceptible places to climate change on the planet. Furthermore, sea ice affects

3311-609: The annual cycle of solar insolation and of ocean and atmospheric temperature and of variability in this annual cycle. In the Arctic, the area of ocean covered by sea ice increases over winter from a minimum in September to a maximum in March or sometimes February, before melting over the summer. In the Antarctic, where the seasons are reversed, the annual minimum is typically in February and the annual maximum in September or October and

3388-498: The atmosphere in the late 19th century. Other EBMs similarly seek an economical description of surface temperatures by applying the conservation of energy constraint to individual columns of the Earth-atmosphere system. Essential features of EBMs include their relative conceptual simplicity and their ability to sometimes produce analytical solutions . Some models account for effects of ocean, land, or ice features on

3465-504: The basic laws of physics , fluid motion , and chemistry . Scientists divide the planet into a 3-dimensional grid and apply the basic equations to those grids. Atmospheric models calculate winds , heat transfer , radiation , relative humidity , and surface hydrology within each grid and evaluate interactions with neighboring points. These are coupled with oceanic models to simulate climate variability and change that occurs on different timescales due to shifting ocean currents and

3542-415: The bottom of the ocean. This cold water moves along the ocean floor towards the equator, while warmer water on the ocean surface moves in the direction of the poles. This is referred to as " conveyor belt motion" and is a regularly occurring process. In order to gain a better understanding about the variability, numerical sea ice models are used to perform sensitivity studies . The two main ingredients are

3619-413: The climate system in full 3-D space and time was impractical prior to the establishment of large computational facilities starting in the 1960s. In order to begin to understand which factors may have changed Earth's paleoclimate states, the constituent and dimensional complexities of the system needed to be reduced. A simple quantitative model that balanced incoming/outgoing energy was first developed for

3696-499: The coastline. Only the top layer of water needs to cool to the freezing point. Convection of the surface layer involves the top 100–150 m (330–490 ft), down to the pycnocline of increased density. In calm water, the first sea ice to form on the surface is a skim of separate crystals which initially are in the form of tiny discs, floating flat on the surface and of diameter less than 0.3 cm (0.12 in). Each disc has its c-axis vertical and grows outwards laterally. At

3773-465: The coupled atmosphere–ocean– sea ice global climate models . These types of models solve the full equations for mass transfer, energy transfer and radiant exchange. In addition, other types of models can be interlinked. For example Earth System Models include also land use as well as land use changes . This allows researchers to predict the interactions between climate and ecosystems . Climate models are systems of differential equations based on

3850-416: The dynamics of the climate system and to make projections of future climate and of climate change . Climate models can also be qualitative (i.e. not numerical) models and contain narratives, largely descriptive, of possible futures. Climate models take account of incoming energy from the Sun as well as outgoing energy from Earth. An imbalance results in a change in temperature . The incoming energy from

3927-423: The effect of ice-albedo feedback on global climate sensitivity has been investigated using a one-dimensional radiative-convective climate model. The zero-dimensional model may be expanded to consider the energy transported horizontally in the atmosphere. This kind of model may well be zonally averaged. This model has the advantage of allowing a rational dependence of local albedo and emissivity on temperature –

SECTION 50

#1732769140809

4004-403: The first "ice free" Arctic summer might occur vary. Antarctic sea ice extent gradually increased in the period of satellite observations, which began in 1979, until a rapid decline in southern hemisphere spring of 2016. Sea ice provides an ecosystem for various polar species, particularly the polar bear , whose environment is being threatened as global warming causes the ice to melt more as

4081-712: The grey ice stage) or ridge (at the grey-white ice stage). First-year sea ice is ice that is thicker than young ice but has no more than one year growth. In other words, it is ice that grows in the fall and winter (after it has gone through the new ice – nilas – young ice stages and grows further) but does not survive the spring and summer months (it melts away). The thickness of this ice typically ranges from 0.3 m (0.98 ft) to 2 m (6.6 ft). First-year ice may be further divided into thin (30 cm (0.98 ft) to 70 cm (2.3 ft)), medium (70 cm (2.3 ft) to 120 cm (3.9 ft)) and thick (>120 cm (3.9 ft)). Old sea ice

4158-403: The ice also serves a role in maintaining cooler polar temperatures by reflecting much of the sunlight that hits it back into space. As the sea ice melts, its surface area shrinks, diminishing the size of the reflective surface and therefore causing the earth to absorb more of the sun's heat. As the ice melts it lowers the albedo thus causing more heat to be absorbed by the Earth and further increase

4235-422: The ice growth period, its bulk brine volume is typically below 5%. Air volume fraction during ice growth period is typically around 1–2 %, but may substantially increase upon ice warming. Air volume of sea ice in can be as high as 15 % in summer and 4 % in autumn. Both brine and air volumes influence sea-ice density values, which are typically around 840–910 kg/m for first-year ice. Sea-ice density

4312-571: The ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids, which in turn provide food for animals such as krill and specialised fish like the bald notothen , fed upon in turn by larger animals such as emperor penguins and minke whales . A decline of seasonal sea ice puts the survival of Arctic species such as ringed seals and polar bears at risk. Other element and compounds have been speculated to exist as oceans and seas on extraterrestrial planets. Scientists notably suspect

4389-426: The ice surface during the melt season lower the albedo such that more solar radiation is absorbed, leading to a feedback where melt is accelerated. The presence of melt ponds is affected by the permeability of the sea ice (i.e. whether meltwater can drain) and the topography of the sea ice surface (i.e. the presence of natural basins for the melt ponds to form in). First year ice is flatter than multiyear ice due to

4466-484: The interaction between fast ice and the drifting pack ice. Level ice is sea ice that has not been affected by deformation and is therefore relatively flat. Leads and polynyas are areas of open water that occur within sea ice expanses even though air temperatures are below freezing and provide a direct interaction between the ocean and the atmosphere, which is important for the wildlife. Leads are narrow and linear – they vary in width from meter to km scale. During

4543-650: The lack of dynamic ridging, so ponds tend to have greater area. They also have lower albedo since they are on thinner ice, which blocks less of the solar radiation from reaching the dark ocean below. Sea ice is a composite material made up of pure ice, liquid brine, air, and salt. The volumetric fractions of these components—ice, brine, and air—determine the key physical properties of sea ice, including thermal conductivity, heat capacity, latent heat, density, elastic modulus, and mechanical strength. Brine volume fraction depends on sea-ice salinity and temperature, while sea-ice salinity mainly depends on ice age and thickness. During

4620-407: The movement of ocean waters. In the freezing process, much of the salt in ocean water is squeezed out of the frozen crystal formations, though some remains frozen in the ice. This salt becomes trapped beneath the sea ice, creating a higher concentration of salt in the water beneath ice floes. This concentration of salt contributes to the salinated water's density and this cold, denser water sinks to

4697-412: The much larger heat storage capacity of the global ocean. External drivers of change may also be applied. Including an ice-sheet model better accounts for long term effects such as sea level rise . There are three major types of institution where climate models are developed, implemented and used: Big climate models are essential but they are not perfect. Attention still needs to be given to

SECTION 60

#1732769140809

4774-518: The nature of questions asked and the pertinent time scales, there are, on the one extreme, conceptual, more inductive models, and, on the other extreme, general circulation models operating at the highest spatial and temporal resolution currently feasible. Models of intermediate complexity bridge the gap. One example is the Climber-3 model. Its atmosphere is a 2.5-dimensional statistical-dynamical model with 7.5° × 22.5° resolution and time step of half

4851-489: The ocean. Depending on location, sea ice expanses may also incorporate icebergs. Sea ice does not simply grow and melt. During its lifespan, it is very dynamic. Due to the combined action of winds, currents, water temperature and air temperature fluctuations, sea ice expanses typically undergo a significant amount of deformation. Sea ice is classified according to whether or not it is able to drift and according to its age. Sea ice can be classified according to whether or not it

4928-531: The planet's surface, have an average emissivity of about 0.5 (which must be reduced by the fourth power of the ratio of cloud absolute temperature to average surface absolute temperature) and an average cloud temperature of about 258 K (−15 °C; 5 °F). Taking all this properly into account results in an effective earth emissivity of about 0.64 (earth average temperature 285 K (12 °C; 53 °F)). Dimensionless models have also been constructed with functionally separated atmospheric layers from

5005-520: The poles can be allowed to be icy and the equator warm – but the lack of true dynamics means that horizontal transports have to be specified. Early examples include research of Mikhail Budyko and William D. Sellers who worked on the Budyko-Sellers model . This work also showed the role of positive feedback in the climate system and has been considered foundational for the energy balance models since its publication in 1969. Depending on

5082-566: The presence of sea ice abutting the calving fronts of ice shelves has been shown to influence glacier flow and potentially the stability of the Antarctic ice sheet . The growth and melt rate are also affected by the state of the ice itself. During growth, the ice thickening due to freezing (as opposed to dynamics) is itself dependent on the thickness, so that the ice growth slows as the ice thickens. Likewise, during melt, thinner sea ice melts faster. This leads to different behaviour between multiyear and first year ice. In addition, melt ponds on

5159-461: The radiative heat transfer processes which underlie the greenhouse effect. Quantification of this phenomenon using a version of the one-layer model was first published by Svante Arrhenius in year 1896. Water vapor is a main determinant of the emissivity of Earth's atmosphere. It both influences the flows of radiation and is influenced by convective flows of heat in a manner that is consistent with its equilibrium concentration and temperature as

5236-437: The real world (what is happening and why). The global models are essential to assimilate all the observations, especially from space (satellites) and produce comprehensive analyses of what is happening, and then they can be used to make predictions/projections. Simple models have a role to play that is widely abused and fails to recognize the simplifications such as not including a water cycle. A general circulation model (GCM)

5313-506: The solar constant, Earth albedo, or effective Earth emissivity. The effective emissivity also gauges the strength of the atmospheric greenhouse effect , since it is the ratio of the thermal emissions escaping to space versus those emanating from the surface. The calculated emissivity can be compared to available data. Terrestrial surface emissivities are all in the range of 0.96 to 0.99 (except for some small desert areas which may be as low as 0.7). Clouds, however, which cover about half of

5390-494: The surface budget. Others include interactions with parts of the water cycle or carbon cycle . A variety of these and other reduced system models can be useful for specialized tasks that supplement GCMs, particularly to bridge gaps between simulation and understanding. Zero-dimensional models consider Earth as a point in space, analogous to the pale blue dot viewed by Voyager 1 or an astronomer's view of very distant objects. This dimensionless view while highly limited

5467-595: The surface. The simplest of these is the zero-dimensional, one-layer model , which may be readily extended to an arbitrary number of atmospheric layers. The surface and atmospheric layer(s) are each characterized by a corresponding temperature and emissivity value, but no thickness. Applying radiative equilibrium (i.e conservation of energy) at the interfaces between layers produces a set of coupled equations which are solvable. Layered models produce temperatures that better estimate those observed for Earth's surface and atmospheric levels. They likewise further illustrate

5544-440: The temperature variation with elevation in a more realistic manner. They also simulate the observed decline in upper atmospheric temperature and rise in surface temperature when trace amounts of other non-condensible greenhouse gases such as carbon dioxide are included. Other parameters are sometimes included to simulate localized effects in other dimensions and to address the factors that move energy about Earth. For example,

5621-469: The web: Sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions : the Arctic ice pack of the Arctic Ocean and

5698-687: The whole continent. The principal proxy that tracks atmospheric cooling in Antarctic ice cores are the deuterium signatures which show negative deviations between 14,000 and 12,500 years BP. CO 2 concentrations have also been shown to consistently drop during this period in these ice cores. Southern South America has well conserved evidences of climatic cooling during the ACR. Stratigraphic records from southern Patagonia (45°-54°S) show ecological changes associated with climatic cooling or increased precipitation. For example, pollen records show cold tolerant and alpine vegetation that shifted to Rain forest vegetation after 12,500 years BP. New Zealand features

5775-464: The winter, the water in leads quickly freezes up. They are also used for navigation purposes – even when refrozen, the ice in leads is thinner, allowing icebreakers access to an easier sail path and submarines to surface more easily. Polynyas are more uniform in size than leads and are also larger – two types are recognized: 1) Sensible-heat polynyas , caused by the upwelling of warmer water and 2) Latent-heat polynyas , resulting from persistent winds from

5852-568: Was developed in the late 1960s at the Geophysical Fluid Dynamics Laboratory , a component of the U.S. National Oceanic and Atmospheric Administration . By 1975, Manabe and Wetherald had developed a three-dimensional global climate model that gave a roughly accurate representation of the current climate. Doubling CO 2 in the model's atmosphere gave a roughly 2 °C rise in global temperature. Several other kinds of computer models gave similar results: it

5929-520: Was impossible to make a model that gave something resembling the actual climate and not have the temperature rise when the CO 2 concentration was increased. The Coupled Model Intercomparison Project (CMIP) has been a leading effort to foster improvements in GCMs and climate change understanding since 1995. The IPCC stated in 2010 it has increased confidence in forecasts coming from climate models: "There

#808191