Climate Models: Components & Evolution

Climate models include numerous elements of Earth's climate system, such as clouds, rainfall, sunlight, sea ice, oceans, evaporation, and so on.

These diagrams depict the evolution of climate models, and the features included in them, over the years. Early models (in the 1970s) were relatively simple; they used just a few key features (incoming sunlight, rainfall, and CO2 concentration) to represent Earth's climate system. Models grew more sophisticated over time, incorporating clouds, land surface features, ice, and other elements into their calculations. Simple oceans were included in models beginning around the time of the IPCC's First Assessment Report (FAR) in the early 1990s; later models include more complex representations of oceans. Current climate models include clouds, a broader range of atmospheric constituents (sulphates, aerosols, etc.) and atmospheric chemistry, vegetation that exchanges gases with the atmosphere, and other features. The FAR, SAR, TAR, and AR4 labels on the diagrams indicate the models in use at the times of each of the four IPCC Assessment Reports. Credits: Images courtesy of the IPCC (AR4 WG 1 Chapter 1 page 99 Fig. 1.2).

The image below illustrates the many components of a modern climate model, in this case NCAR's Community Climate System Model (CCSM).

Components of a modern climate model - NCAR's Community Climate System Model. The various components are described below. Credits: Image courtesy of UCAR; illustration by Paul Grabhorn.

Cirrus clouds

These high, thin, icy clouds act as a warming influence on climate overall, because they allow sunlight in but trap long-wave radiation rising from Earth’s heated surface. The CCSM depicts these and other clouds throughparameterization - tracking the conditions that form such clouds and then specifying how much of a given rectangle of land in the model grid is covered by each cloud type.

Stratus clouds

These low, dense, very reflective clouds act as a cooling influence on climate overall, because they reflect a great deal of sunlight. Subtropical oceans often feature huge areas of marine stratocumulus. The CCSM depicts these and other clouds through parameterization - tracking the conditions that form such clouds and then specifying how much of a given rectangle of land in the model grid is covered by each cloud type.

Cumulus clouds

These puffy clouds, which sometimes build in tower-like formations, are linked to strong updrafts and the showers and thunderstorms that result. Cumulus are difficult to represent in models because each cloud covers only a small part of Earth’s surface, but when taken together, cumulus clouds have a large influence on global circulation. The CCSM depicts these and other clouds through parameterization - tracking the conditions that form such clouds and then specifying how much of a given rectangle of land in the model grid is covered by each cloud type.

Precipitation and evaporation

The process of converting water vapor to water droplets or snowflakes releases heat into the atmosphere. The CCSM simulates this process, as well as the evaporation of water from soil, wetlands, lakes, and oceans and the amount of rain or snow reaching the surface.

Sea ice

Sea ice helps keep polar regions cold, because it reflects most of the sunlight that hits it. When sea ice melts, it does not raise sea level directly (because the ice is already afloat, like a melting ice cube in a glass of water). However, the dark surface ocean exposed by melting sea ice absorbs most of the sunlight it receives, which leads to further warming. Research using the CCSM indicates that Arctic summertime sea ice may diminish greatly, as soon as the 2030s.

Winds

One of the main elements of a climate model is its depiction of winds. The global circulation transports warm air poleward and cold air toward the equator. This flow operates through several persistent loops that produce trade winds in the tropics, westerly winds at midlatitudes, and easterlies across the poles. The actual winds at any one spot are influenced by day-to-day weather as well as climate cycles such as El Niño. Where winds converge, rising motion and rain or snow may develop.

Heat and salinity exchange

Because water has a higher heat capacity than soil, it takes longer for sea surfaces to warm up or cool down relative to the continents. Climate models must account for the transfer of heat between ocean and atmosphere. They also need to reflect changes in salinity (salt content) that occur as ocean water evaporates, or as fresh water enters the oceans through increased rainfall or increased glacial melting.

Atmospheric model layers

Contrasts in temperature and wind are much stronger vertically than horizontally. Only a few miles above ground, temperatures are usually frigid (even in summer), and winds may howl at 200 miles per hour (320 kilometers per hour) or more. The CCSM divides the atmosphere into 26 layers, tracking each layer as well as exchanges of energy and moisture between layers. Near the ground, where vertical contrasts are strongest, the layers (which are defined by atmospheric pressure) can be as thin as 1,000 feet (about 300 meters) or less.

Ocean currents, temperature, and salinity

The behavior of the ocean is much more difficult to observe than the atmosphere, and many ocean processes are still poorly understood. As recently as the 1990s, most climate models used a “slab” ocean—one that behaves as a single unit. Today, the CCSM and other sophisticated models include a much more dynamic depiction of the ocean that tracks changes in ocean currents, temperature, and salinity. These control such phenomena as the North Atlantic’s overturning circulation, which helps keep Europe warm for its latitude but which may be sensitive to climate change.

Ocean model layers

Much like the atmosphere, the ocean needs to be divided into several layers in order for a model to accurately depict the three-dimensional flow and other qualities. The CCSM includes 40 ocean layers, ranging in thickness from about 33 feet (10 meters) near the sea surface to about 800 feet (250 meters) in the deep ocean.

Ocean bottom topography

In order to accurately depict the ocean circulation in three dimensions, the CCSM includes undersea ridges, valleys, and other topographic features of the ocean bottom.

Vertical overturning

Most of the world’s oceans outside the Arctic feature a relatively warm sea surface and a thin region called a thermocline that separates the warm surface layer from colder, deeper waters. In some parts of the world, colder and deeper water regularly crosses the thermocline to mix with warmer surface waters, or vice versa. The CCSM can simulate these overturning processes.

Realistic geography

Large mountain chains exert a major influence on temperature, precipitation, and wind patterns for miles around. Even when mountains are relatively modest in size or extent, they play an important role in local climate. Early climate models tracked the atmosphere at points separated by hundreds of miles, so mountain ranges appeared in highly smoothed form. The CCSM and other contemporary models operate at higher resolution so the topography is much less smoothed.

Land surface processes

The atmosphere is strongly affected by what lies beneath it - forests, deserts, ice sheets, mountains, and grasslands. The CCSM includes each of these elements, tracking the exchange of energy and moisture between them and the atmosphere. Urban areas are not yet depicted in the standard version of the CCSM or other global climate models, although work is under way to add them.

Soil moisture

Moisture stored near and just below ground level affects how much rain and snow can be absorbed by the soil and how quickly a region dries out if precipitation slackens. The CCSM includes a depiction of moisture in 10 soil layers.

Outgoing heat energy

Virtually all of the energy that reaches our planet from the Sun leaves the Earth system in one form or another. In order to keep their simulation of Earth’s climate in proper balance, the CCSM and other climate models account for this outgoing radiation.

Incoming solar energy

To create an accurate portrayal of Earth’s climate, the CCSM calculates the amount of incoming solar radiation by location, time of day, and time of year. When reproducing past climates, the model can also include estimates of solar variability based on sunspot counts, carbon dating of organic material, and other indirect evidence.

Transition from solid to vapor

Besides melting, snowpacks can erode through a process called sublimation, in which moisture goes directly from ice crystals to water vapor in the atmosphere. Sublimation is common in dry mountain climates, where a snowpack may leave little or no water behind as it shrinks (even in temperatures below freezing). The CCSM depicts sublimation as well as snowmelt.

Evaporative and heat energy exchanges

When water evaporates, it draws heat from the lakes, rivers, or oceans from which it came and stores that heat within its molecular bonds. Heat can also leave the land and ocean surface directly through contact between the surface and molecules in the atmosphere (a process called conduction). The CCSM depicts these and other processes that move heat energy around the Earth system.

Snow cover

Large areas of snow have a major effect on weather. Because of their light color, they reflect large amounts of sunlight and help keep temperatures colder than they would otherwise be, especially close to the ground. The CCSM tracks the seasonal waxing and waning of snowfall across mountainous and high-latitude areas. The large ice sheets in Greenland and Antarctica are also included. Some of the processes that control ice sheets are still being studied by scientists and are not yet part of the CCSM and other global models.

Runoff

A key part of the global water cycle is the flow of water from rivers, lakes, and land areas down toward the sea. The CCSM depicts runoff more precisely than earlier models, which enhances its treatment of the water cycle overall.

Last modified: 29 November 2010
Created: 29 November 2010

Source:http://eo.ucar.edu/staff/rrussell/climate/modeling/climate_model_components_evolution.html

Climate Models

Excerpts from:

Climate Models and Their Evaluation, In: Climate Change 2007: The Physical Science Basis, Chapters 8 and 10

Ch 8 http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter8.pdf

Ch 10 http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter10.pdf

Climatic Research Unit (CRU) website: http://www.cru.uea.ac.uk/

What are climate models?

Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the weather and climate system to projections of future climate. All climate models balance, or very nearly balance, incoming energy as short wave electromagnetic radiation (visible and ultraviolet) to the earth with outgoing energy as long wave (infrared) electromagnetic radiation from the earth. Any imbalance results in a change in the average temperature of the earth.

There have been major advances in the development and use of models over the last 20 years and the current models give us a reliable guide to the direction of future climate change. Computer models cannot predict the future exactly, due to the large number of uncertainties involved. The models are based mainly on the laws of physics, but also empirical techniques which use, for example, studies of detailed processes involved in cloud formation. The most sophisticated computer models simulate the entire climate system. As well as linking the atmosphere and ocean, they also capture the interactions between the various elements, such as ice and land (CRU).

Climate models have been used successfully to reproduce the main features of the current climate; the temperature changes over the last hundred years, and the main features of the Holocene (6,000 years ago) and Last Glacial Maximum (21,000) years ago. Current models enable us to attribute the causes of past climate change, and predict the main features of the future climate, with a high degree of confidence (CRU).

The most talked-about models of recent years have been those relating temperature to emissions of carbon dioxide (and other greenhouse gases). These models project an upward trend in the surface temperature record, as well as a more rapid increase in temperature at higher altitudes.

Coupled atmosphere-ocean general circulation models (AOGCMs)

(e.g. MIROC3.2(medres), CSIRO-MK3.0, UKMO-HadCM3)

Climate models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry. To “run” a model, scientists divide the planet into a 3-dimensional grid, apply the basic equations, and evaluate the results. Atmospheric models calculate winds, heat transfer, radiation, relative humidity, and surface hydrology within each grid and evaluate interactions with neighboring points.

From: NOAA http://celebrating200years.noaa.gov/breakthroughs/climate_model/welcome.html

AOGCMs combine the two general circulation models, atmospheric and ocean. They thus have the advantage of removing the need to specify fluxes across the interface of the ocean surface. These models are the basis for sophisticated model predictions of future climate, such as are discussed by the IPCC. AOGCMs represent the pinnacle of complexity in climate models and internalize as many processes as possible. They are the only tools that could provide detailed regional predictions of future climate change. However, they are still under development. The simpler models are generally susceptible to simple analysis and their results are generally easy to understand. AOGCMs, by contrast, are often nearly as hard to analyze as the real climate system (Randall, 2007).

Atmosphere-Ocean General Circulation Models are able to simulate extreme warm temperatures, cold air outbreaks and frost days reasonably well. Models used in Fourth Assessment Report (AR4 2007) for projecting tropical cyclone changes are able to simulate present day frequency and distribution of cyclones, but intensity is less well simulated. Simulation of extreme precipitation is dependent on resolution, parameterization, and the thresholds chosen. In general, models tend to produce too many days with weak precipitation (<10 mm day–1) and too little precipitation overall in intense events (>10 mm day–1) (Randall, 2007).

The large-scale patterns of seasonal variation in several important atmospheric fields are now better simulated by AOGCMs than they were at the time of the Third Assessment Report (TAR 2001). Notably, errors in simulating the monthly mean, global distribution of precipitation, sea level pressure and surface air temperature have all decreased. In some models, simulation of marine low-level clouds, which are important for correctly simulating sea surface temperature and cloud feedback in a changing climate, has also improved. Nevertheless, important deficiencies remain in the simulation of clouds and tropical precipitation (with their important regional and global impacts) (Randall, 2007).

Since the TAR, developments in AOGCM formulation have improved the representation of large-scale variability over a wide range of time scales. The models capture the dominant extratropical patterns of variability including the Northern and Southern Annular Modes, the Pacific Decadal Oscillation, the Pacific-North American and Cold Ocean-Warm Land Patterns. AOGCMs simulate Atlantic multi-decadal variability, although the relative roles of high- and low-latitude processes appear to differ between models. In the tropics, there has been an overall improvement in the AOGCM simulation of the spatial pattern and frequency of ENSO, but problems remain in simulating its seasonal phase locking and the asymmetry between El Niño and La Niña episodes (Randall, 2007).

How Reliable Are the Models Used to Make Projections of Future Climate Change?

Excerpt from: Frequently Asked Question 8.1.Climate Models and Their Evaluation, In: Climate Change 2007: The Physical Science Basis, Chapter 8, pages 600-601.

There 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 a robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases (Randall, 2007).

Global mean near-surface temperatures over the 20^th century from observations (black) and as obtained from 58 simulations produced by 14 different climate models driven by both natural and human-caused factors that influence climate (yellow). The mean of all these runs is also shown (thick red line). Temperature anomalies are shown relative to the 1901 to 1950 mean. Vertical grey lines indicate the timing of major volcanic eruptions. (Figure adapted from Chapter 9, Figure 9.5, IPCC 2007: Climate Change 2007: The Physical Science Basis. Refer to corresponding caption for further details.)

Supporting Documentation

Randall, D.A., R.A. Wood, S. Bony, R. Colman, T. Fichefet, J. Fyfe, V. Kattsov, A. Pitman, J. Shukla, J. Srinivasan, R.J. Stouffer, A. Sumi and K.E. Taylor, 2007: Climate Models and Their Evaluation. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning,

Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter8.pdf

Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper, I.G. Watterson, A.J. Weaver and Z.-C. Zhao, 2007: Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter10.pdf

IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

http://www.ipcc.ch/ipccreports/ar4-wg1.htm

IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf

IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp.

http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

IPCC, 2000: Emissions Scenarios. Nebojsa Nakicenovic and Rob Swart (Eds.), Cambridge University Press, UK. pp 570. Available from Cambridge University Press, The Edinburgh Building Shaftesbury Road, Cambridge CB2 2RU ENGLAND

http://www.ipcc.ch/ipccreports/sres/emission/index.htm

Archive for the ‘refuting the skeptics’ Category

Record setting 2010 Greenland temperatures and long term trends

Thursday, January 20th, 2011

Year 2010 surface air temperature observations around west and south Greenland are unprecedented in the instrumental record. Year 2010 and year 2003 temperatures dwarf high yearly averages occurring in the 1920s and 1930s.

Warming and Cooling

Fig. 1. 170 years of annually resolved whole Greenland ice sheet averaged surface air temperature from a reconstruction driven by a statistical fusion of long term meteorological station data with calibrated regional climate data assimilation model output (Box et al. 2009). A pink circle denotes the record setting year 2010 value.The thick gray line is a 31 year two-tailed Gaussian-weighted smoothing of the annual values. As the "boxcar" gets within 15 years of the beginning and end of the series, the "tail" that runs into the end of the series is cut off and the weighting shifts accordingly.

Over the full 171 years (1840-2010) of the reconstruction, the ice sheet average surface air temperature increased 1.26 C. The warming rate was 0.74 C/century. The recent 17 year Greenland ice sheet warming rate is 30% smaller in magnitude than a 17 year period in the 1920s. The intervening 63 year period (1932 to 1992) was cooling at -0.19 C/decade. This  cooling can be attributed to a cooling phase of theAtlantic Multidecadal Oscillation (AMO) (e.g. Schesinger et al. 1994; Trenberth et al. 2006). Cold episodes in 1983-84 and 1991-92 enhance this cooling trend and are caused primarily by major volcanic eruptions (see Box, 2002) . West Greenland is a focus of sulfate aerosol-induced cooling (see Box et al. 2009). Another contributor to the 1932 to 1992 cooling is global dimming, that is, cooling at the surface induced by increases in atmospheric aerosols. Liepert et al (2002) estimated that there was globally a reduction of about 4% in solar radiation reaching the ground between 1961 and 1990. The Wikipedia Global Dimming article is worth reading. The recent (post-1994) warming, is attributable to: 1.) a growing absence of sulfate cooling because there has not been a major volcanic eruption since 1991; 2) recent warming phase of AMO; 3) an apparent  reversal of the global dimming trend; and 4) ongoing and intensifying anthropogenic global warming (AWG), the elephant in the room, owing to a dominance of enhanced greenhouse effect despite other anthropogenic cooling factors such as aerosols and contrails (IPCC, 2007). The primary factor responsible for the warming trend is very likely to be AWG (IPCC, 2007).

Fig. 2. Three long term Greenland meteorological station records, illustrating the long term time series of yearly-average temperatures. Triangles denote record setting values coinciding in 2010. Also interesting to note is the strong 1983-1984 El Chichon volcanic cooling (see Box 2002).

Refuting Denial

It is scientific to question if year 2010 record setting temperatures are real or due to some spurious aspect of the measurements. Former television meteorologist Anthony Watts, for one, expended quite a lot of effort to discredit apparent record setting 2010 temperatures in Nuuk, Greenland. However, Watts seems in error, as one would not expect the same pattern at other locations and in independent periods of time (Fig. 2), if the Nuuk 2010 temperatures are spurious. Rather, record high temperatures are evident at other Greenland stations in the same months, for example, in May, August, September, November, December 2010. Watts implicates the fact that the Nuuk measurements are near an airport to discredit the anomalous year 2010 values. Heat spewing from airplanes seems a valid concern and incidentally Aasiaat measurements are also from the grounds of an airport. However, the Prince Christian Sound (a.k.a. Prins Christian Sund) data are not obtained from near any airport (J. Cappelen, DMI, personal communication).

Acknowledgement

We are fortunate to have continuous temperature records from Greenland’s capital Nuuk beginning in 1866 in addition to century-plus records from other locations in Greenland (Box 2002; Vinther et al. 2006; Cappelen 2010; Box et al. 2009), providing instrumental climate records rivaling many of the longest records on Earth. I have used these data record and others available from the Danish Meteorological Institute and NASA to reconstruct Greenland ice sheet average surface air temperatures (see Box et al. 2009). I update the Box et al. (2009) reconstruction and make further analysis in this blog entry. This work is in preparation for my 7th consecutive annual Greenland entry for the Bulletin of the American Meteorological Society’s “State of the Climate” report published each June.

Sources

• Box, J.E., 2002: Survey of Greenland instrumental temperature records: 1873-2001, International Journal of Climatology, 22, 1829-1847. PDF
• Box, J.E., L. Yang, D.H. Browmich, L-S. Bai, 2009: Greenland ice sheet surface air temperature variability: 1840-2007, J. Climate, 22(14), 4029-4049, doi:10.1175/2009jcli2816.1. PDF
• Cappelen J., 2010: DMI Monthly Climate Data Collection 1768-2009, Denmark, The Faroe 263 Islands and Greenland Dansk Meterologisk Institut Technical report No. 10-05
• Intergovernmental Panel on Climate Change (IPCC) (2007), Climate Change 2007: The Physical Science Basis, edited by S. Solomon et al., Cambridge Univ. Press, New York.
• Liepert, B. G. (2002), Observed reductions of surface solar radiation at sites in the United States and worldwide from 1961 to 1990, Geophys. Res. Lett., 29(10), 1421, doi:10.1029/2002GL014910.
• Schlesinger, M.E. and Navin Ramankutty (1994): An oscillation in the global climate system of period 65-70 years. Nature, 367, Issue 6465, pp. 723-726, DOI: 10.1038/367723a
• Trenberth, K.E. and D.J. Shea (2006): Atlantic hurricanes and natural variability in 2005. Geophysical Research Letters 33, L12704, doi:10.1029/2006GL026894 PDF
• Vinther, B. M., K. K. Andersen, P. D. Jones, K. R. Briffa, and J. Cappelen, 2006: Extending Greenland temperature records into the late eighteenth century. J. Geophys. Res., 111, D11105,
  doi:10.1029/2005JD006810.

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