Climate models and scenarios

A bridge over a dry riverClick to enlarge
Heat waves can lead to low water and affect shipping.
Source: Arno Bachert/Fotolia.com

In order to be able to prepare ourselves for climate impacts, we need to know how the climate might change in the future. Climate models are used for this purpose.

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What are climate models?

Climate models are extensive computer programmes that rely on certain assumptions when calculating the future development of the climate. These assumptions are summarised in emissions and concentration scenarios. This results in climate projections. They form the basis for the assessment of risks and chances of future changes in climate and for the development of adaptation strategies.

What are scenarios and what are they used for?

Scenarios play an important role for the calculation of potential climate changes. The scenarios are based on a number of assumptions that concern different global trends such as population growth, economic and social developments, technological changes, consumption of resources and environmental management. On the basis of these assumptions it is possible to comment on how the emission of greenhouse gases (emissions scenarios) and, as a result, the concentration of greenhouse gases in the atmosphere (concentration scenarios) will develop. The majority of current climate projections are based on the SRES-Emissions Scenarios of the Intergovernmental Panel on Climate Change (IPCC).

New scenarios have been developed for the Fifth Assessment Report of the IPCC. They are referred to as Representative Concentration Pathways (abbreviated RCPs) and linked to Integrated Assessment Models (IAM). They reflect the energy system, the climate system, the economy and land use. Therefore, scenarios that are derived from Integrated Assessment Models essentially cover all factors that influence greenhouse gas emissions by humans and allow for plausible projections of possible climate changes.
Although there are still a few uncertainties, climate models constitute an important source of information for the structuring of mitigation and adaptation measures.

 

Are there any regional climate models for Germany?

Quite often, climate models at a global scale have a rather coarse resolution and are geographically imprecise. In order to better align the climate projections with the specific circumstances in Germany, the models are specified locally. There are two methods for such a regionalisation of global climate models: dynamic and statistic processes. Two examples are the models REMO (dynamic) and WETTREG (statistic).

Dynamic regional models simulate different climate parameters by solving non-linear equations for regional sections of the global model. These simulations are based on input data provided by the global model. By focusing on a smaller region it is possible to obtain a larger spatial and temporal resolution with the same computing capacity.

Statistic regional models rely on knowledge that is based on specific climate observations. WETTREG, for example, refers to established statistical connections between large-scale circulation patterns in the atmosphere and local and regional weather events. The simulation of circulation patterns in the atmosphere relies on global models. Possible regional developments can be calculated on this basis. Similar to the global models, the results of regional model runs are referred to as (regional) climate projections.

How are uncertainties dealt with?

Climate projections always involve uncertainties. Even if climate models were capable of reproducing the correlations in the atmosphere accurately, uncertainties would remain. This results from the fact that scenarios relating to future population growth, economic and social development, technological changes, resource depletion and environmental management always entail uncertain predictions. It is impossible to predict socio-economic developments with absolute certainty. In addition, the accuracy of climate projections diminishes, the further the respective timeframe lies in the future and the smaller the considered region is.

In order to deal with this uncertainty it is important to know how large its range is. Compilations of several climate model results can be used to display this range.

The greater the existing ensemble of model projections, the more accurately uncertainties and margins of fluctuations of the model results can be assessed. The project "ENSEMBLES" merges a number of national and international climate models that are based on the A1B Emissions Scenario and were calculated by the end of the 21st Century into one ensemble approach. As a result, plausible statements about potential climate changes in Europe can be made. The ENSEMBLES project was funded by the Sixth European Research Framework Programme.

 

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