Climate model

A climate model is a computer model for the calculation and projection of the climate for a certain period of time. The model is usually based on a meteorological model, as it is also used for numerical weather prediction. This model is, however, extended for the climate modeling to map all conserved quantities correctly. As a rule, an ocean model, a snow - and ice models for the cryosphere and vegetation model for the biosphere coupled.

Mathematics is created by a coupled system of nonlinear partial and ordinary differential equations and some algebraic equations. The numerical calculation of this system of equations requires a very large computational power, as provided by supercomputers like the Earth Simulator.

We distinguish between global climate models ( GCMs called, general circulation models ) and regional climate models. The main difference is due to the fact that a global climate model includes the entire troposphere, while a regional model generally reflects the same model physics, but this applies only to a particular geographical section of the earth.

General

Climate models represent the most complex and computationally elaborate computer models that have been developed. The " projections " of the climate models are inherently more uncertain than that of the weather models, because here much longer periods taken into consideration and a large number of additional parameters must be considered. For this reason, one speaks of these individual models and climate scenarios and not of climate predictions. A weather forecast is based on data which makes it possible to predict within a span of currently up to a week, the development of chaotic dynamics within the Earth's atmosphere with a high probability. However, the uncertainty of the extrapolation increases exponentially with the projected period and depends itself inter alia on the weather. While playing even when weather models have the experience and assessment of the user in the form of a control function between the pure computer model and the final prediction a crucial role, but the character of a climate model thereof is still fundamentally different.

Climate models are used to find possible trends in the development of the climate and the weighting of individual environmental factors. They are based on a number of assumptions and methods, such as the development of future greenhouse gas emissions and feedback mechanisms. In addition, climate models are based, in contrast to the weather models not on a fixed dynamics and are therefore not restricted by its chaotic character and the limitation of computing power. Many feedbacks are unknown and also from the climate history can these usually no statements are made.

Role of climate models in the simulation of the course and consequences of global warming

To test whether the parameters with which climate models are expected, are correct, they are tested whether they can check the current, but also the climate during the ice ages simulate correctly. In the context of such simulations over 1000 models are expected, with input parameters are varied within their assumed fault width. Models that reflect the temperature variation in the period is incorrect ( > 90%) are sorted out.

Although has expanded dramatically since the 1980s, the knowledge of paleoclimatology, the available data on the climate history to date is incomplete; due to the speed as well as the level of expected future global warming, you probably entered " uncharted territory " with some unforeseen consequences.

The data required for the modeling conditions are therefore only partially known and have to be defined more or less arbitrarily, as a rule, which is called a set of these determinations and the modeling based thereon as climate scenario. The difference between a climate prediction and climate scenario is that you modeled for the former a variety of different scenarios, on the one hand to other models and on the other hand with other presuppositions. A climate prediction based on the analysis of various modeling experiments and is also due to difficult comparisons between them to create very difficult and at enormous expense. Since the individual scenarios, which are also reflected in the structure of the Intergovernmental Panel on Climate Change, have different end results, even basing climate prediction can show only the range of possibilities. In the case of global warming this range corresponds to a possible warming of the average global surface air temperature and from 1.1 to 6.4 ° C by 2100 (IPCC 2007). However, similar variation ranges show up in nearly all extrapolations derived from climate models.

In the discussion on the development and consequences of global warming, the unreliability of climate models is often used as an argument: Since the climate system consists of an abundance of some as yet unknown feedback, which can never be completely represented in climate models, is not a statement on the development of the global climate with regard to possible global warming. However, this is not so. In the early days of the history of science of global warming calculations were made for climate sensitivity, the results differ only slightly from the current state of knowledge, even though the computer was not yet invented, so simulations did not even exist.

Global climate models - GCM ( General Circulation Model)

A global climate model describes the most important climate-relevant physical processes in the atmosphere, the oceans and the earth's surface. The processes are mapped but this very simplified. In particular the processes of the biosphere be set at the moment or as variables and parameters. However, these variables are system variables and should be able to adapt to global change during the simulation, to submit realistic projections on the future. Such feedback processes coupled systems are the major challenge in modeling at the moment. The models are so extensive that they ( several hundred kilometers grid width ) can only be used in very coarse resolution. The first GCM was created in 1967 by Manabe and Richard Wetherald Syukuro.

Examples of global climate models are:

• HadCM3 ( Hadley coupled model, version 3): This climate model, in addition to some other, for the third (TAR ) and fourth ( AR4 ) used Assessment Report of the IPCC

• HadGEM1 ( Hadley global environment model 1 ): further development of the HadCM3 climate model. It has improved the representation of the influence of clouds and sea ice; has also improved the image of the following parameters: water balance, atmospheric chemistry and the effects of aerosols. The representation of the effects of El Nino, the monsoon and Pacific surface temperatures, however, have deteriorated and are the subject of ongoing research, where progress has already been made.

Regional climate models

Regional climate models consider only a section of the atmosphere and therefore require appropriate boundary conditions at the edges of the simulation domain. These constraints come from simulations of global climate models. It is said, therefore, that a regional climate model is driven by a global climate model. This is called " nesting " or "dynamic downscaling ", and describes the embedding of a regional model with a high spatial resolution in a global climate model with a low spatial resolution. The spacing of the grid points in a global climate model are quite large and are usually between 150 and 500 km. Regional models, however, have a very fine resolution. The grid points are located here at a distance of sometimes only 1 km. Due to the increase of the computing capacity of modern supercomputer, the spatial resolution of the models can be continuously improved.

Examples of regional models are:

• ALADIN - Climate ( standard model Météo -France, ZAMG among others. )
• ARPEGE - Climate model
• CCLM (derived from the local prediction model of the German Weather Service, developed by a community of research institutes and universities)
• COSMO -CLM ( regional model for the Alpine Space )
• MM5 ( Mesoscale Meteorology Model 5; NCAR / NOAA USA)
• RegCM ( ICTP Trieste )
• REMO ( Max Planck Institute for Meteorology in Hamburg )
• PRECIS
• STAR ( statistical model of the PIK)
• WETTREG
• WRF ( modular mesoscale model)

Climate modeling in Germany

In Germany climate models for very different research questions will be used at a variety of universities and research institutes. One of the most central locations is the Max Planck Institute for Meteorology in Hamburg. There, among other things, the global atmospheric models ECHAM -4 and ECHAM 5 and the ocean model MPI -OM were developed. ECHAM and MPI -OM be used depending on the scientific problem also coupled to one another in each case both as stand-alone components, as. Closely linked with the MPI for Meteorology is the neighboring German Climate Computing Centre. There are parallel vector computers are available, as are required for the operation of the models. DKRZ available to other research institutions, among others, to run these models.

The regional climate modeling is carried out, inter alia, major research institutes with different regional models. These research centers include the Karlsruhe Research, GKSS Research Centre in Geesthacht, the Potsdam Institute for Climate Impact Research (PIK ) and some universities. Some of the climate models are developed together with the German Weather Service. In addition to the continuous improvement of numerical models gain ensemble simulations and their probabilistic Interepretation more important.

Many current research projects deal with the issue of interactions between different subsystems of the climate system. Therefore, efforts to integrate next to the atmosphere and ocean other subsystems in the climate models, for example, or cryosphere biosphere. In this context, it is therefore spoken of Earth system models.

Research institutions that deal with the interactions between the atmosphere and biosphere, for example, the Max Planck Institute for Biogeochemistry (Jena), the Max Planck Institute for Meteorology ( Hamburg) or the Potsdam Institute for Climate Impact Research. The Center for Marine Environmental Sciences (Bremen) research on interactions between the biosphere and Physio sphere in the ocean.

ClimatePrediction.net

Main article: ClimatePrediction.net

About the project ClimatePrediction.net a climate model of the University of Oxford is offered for download. Installs on the BOINC software is the free computer time of the home computer to calculate a climate scenario used. In this way, the results of numerous models are compared and possibly weak spots in the models used are improved.

Limits of climate models

When interpreting the results of the current climate model calculations in the future must be considered that it is not mere forecasts over a secure future course of local or global climates, but scenarios that selection of potential gradients on the basis of assumptions about future developments, such example, emissions and land use shown.

The limitations of the models are used in the mathematical models themselves and in the limited number of considered factors. More powerful computers allow it to develop more complex models with higher spatial resolution and an increasing number of factors influencing the climate. In only moderately understood physical principles, currently about the case in the dynamics of ice sheets or the role of aerosols and clouds, climate models can be supplied as only comparatively uncertain results.

In the ice cores in the Arctic recurrent spontaneous climate changes of considerable magnitude are often documented. This can be mapped only insufficiently with today's computer models. Richard B. Alley suggested that essential feedback and side effects in the modeling are not yet considered.

A recent example of a failure of climate models is the unexpectedly high decline in Arctic sea ice cover, as it was observed in summer 2007. He was the result of changes in pressure and circulation patterns that have for some years replaced the previous regime. In none of the climate model, published in the same year, the IPCC climate report such a development had been presented as a way for the coming years.