What will the climate in Europe look like in the middle of the 21st century?

This question is closely related to global warming resulting from human activities such as the combustion of fossil fuels or land-use changes. Consequently, the atmospheric concentrations of greenhouse gases like carbon dioxide, methane and others are expected to rise as well as particulate substances (aerosols) like sulfate or soot which are reflecting part of the sunlight and, thus, tend to counteract the anthropogenic greenhouse effect. The climatic consequences can be estimated with the aid of computer simulations using global climate models which are able to simulate the interactions between phyical processes in different compartments of the climate system (atmosphere, land surface, ocean and sea ice). These model simulations require the projected changes in atmospheric concentrations as input (greenhouse gases and aerosols).

 

The future climate projections documented in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC, 2007) are based on a large set of climate simulations involving 23 global climate models, including that developed at the Max Planck Institute for Meteorology in Hamburg (MPI-M). These model simulations were not only done for the future but also for the recent past (1860-2000) thus enabling to estimate their ability to reproduce the observed climate trends in the 20th century. During this time period the concentrations of the major greenhouse gases (carbon dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons) as well as aerosol concentrations were prescribed according to observations. The future projections according to the emission scenarios B1, A1B and A2 (Nakicenovic et al., 2000) are based on different socioeconomic assumptions including population growth, energy consumption, use of fossil fuels and renewables etc.. The models project a global warming of 1.8°C (range 1.1°C-2.9°C) for B1, 2.8°C (1.7°C-4.4°C) for A1B und 3.4°C (2.0°C-5.4°C) for A2 at the end of the 21st century compared to the time period (1980-1999). In the most extreme (fossil intensive) scenario A1FI the global warming may even exceed 6°C. However, this figure is based on estimates from simple energy balance models.

 

One of the consequences of global warming is the increase of atmospheric water vapour and increased water vapour transport from the ocean to the continents resulting in enhanced precipitation over the continents. There are, however, large regional differences in the precipitation changes. In most models, the precipitation is projected to increase at high latitudes, as already observed, and also in parts of the tropics, whereas the subtropics will suffer from precipitation deficits. Thus, the differences between humid and arid climate zones will be enhanced in a warmer climate.

 

For investigating regional changes in more detail, high-resolution regional models are embedded in global climate models. In this so-called dynamical downscaling approach, the lateral boundary conditions and also the sea surface temperature and sea ice area are provided by the global model so that the global scale climate change can be linked to local consequences in the area of interest. In the following the patterns of temperature and precipitation change in Europe will be shown on the basis model simulations with the MPI-M regional model REMO (Jacob, 2001) driven by data provided by the MPI-M global climate model (Jungclaus et al., 2006). If averaged over the whole integration domain of Europe the models give fairly similar results. However, the regional model resolves the Earth’s surface in much greater detail (orography, vegetation) and, therefore, is able to capture processes like orographic rain more realistically. In addition, the regional model is more successful in simulating extreme weather events that may lead to flooding, for example.

 

Climate projections for the 21st century on the basis of the emission scenarios B1, A1B and A2 were performed with the MPI-M global model (Roeckner et al., 2006) and, for the European domain, with the REMO model using a horizontal resolution of 50 km for REMO and 200 km for the global model.  All simulations were done at the German Climate Computing Centre (DKRZ).

 

Figure 1 shows that the temperature change in the A1B scenario (and in A2 and B1 as well; not shown) is not uniform but characterized by regional and seasonal differences.  In the Mediterranean area the summer temperatures (JJA) increase by more than 2.5°C, in central Europe by less than 1.5°C and in eastern Europe by about 1°C or less. In the winter months (DJF) the simulated warming is typically between 1.5°C and 2°C in a large region extending from Scandinavia to the Mediterranean countries. In regions under direct maritime influence from the Atlantic (Great Britain, Portugal and parts of Spain) the warming during the winter months is less pronounced.

 

Figure 2 shows that the regional and seasonal differences are even more pronounced for the precipitation changes. In the middle of the 21st century the precipitation in the Mediterranean area decreases by up to 50%, in all seasons, whereas in autumn and winter the precipitation increases in large parts of Europe. In the summer months the precipitation decreases not only in the Mediterranean area but also in parts of central and northern Europe, with the largest deficits by more than 30% in France and Great Britain. The latter changes are associated with a gradual northeastward shift of the Azores high.

 

Sources of uncertainties in future climate projections

  • Future emissions
  • Natural climate variability superimposed on anthropogenic trends
  • Formulations of small-scale processes unresolved by the model grid
  • Missing processes

 

Uncertainties in model formulations result, for example, from the difficulty of representing micro-scale cloud and aerosol processes and their interactions. Furthermore, in current climate models the feedbacks between climate change and biogeochemical cycles (carbon, methane, ozone etc.) is generally neglected. Recent studies on the interaction between climate and the carbon cycles actually suggest a positive feedback loop: Global warming as a results of anthropogenic carbon dioxide emissions results in a reduced uptake of carbon by land and ocean so that the atmospheric carbon dioxide concentrations increase further (Friedlingstein et al., 2006). This example underlines the urgency of including biogeochemical cycles in climate models.

 

 

New scenarios


2010/2011 MPI-M simulated new scenarios with the new Earth system model MPI-ESM within the Coupled Model Intercomparison Project Phase 5 (CMIP5). The simulations will be documented in the fifth assessment report of the IPCC in September 2013.

 

December 2007/January 2013

 

Contact: Opens window for sending emailErich Roeckner and Opens window for sending emailAnnette Kirk



Literature:

 

Friedlingstein, P., P. Cox, R. Betts, L. Bopp, W. von Bloh, V. Brovkin, P. Cadule, S. Doney, M. Eby, I. Fung, G. Bala, J. John, C. Jones, F. Joos, T. Kato, M. Kawamiya, W. Knorr, K. Lindsay, H.D. Matthews, T. Raddatz, P. Rayner, C. Reick, E. Roeckner, K.-G. Schnitzler, R. Schnur, K. Strassmann, A.J. Weaver, C. Yoshikawa, and N. Zeng, 2006: Climate-carbon cycle feedback analysis, results from the C4MIP model intercomparison. J. Climate, 19, 3337-3353

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

Jacob, D., 2001: A note to the simulation of the annual and inter-annual variability of the water budget over the Baltic Sea drainage basin, Meteorol Atmos Phys 77, 61-73.

Jungclaus, J.H., N. Keenlyside, M. Botzet, H. Haak, J.-J. Luo, M. Latif, J. Marotzke, U. Mikolajewicz und E. Roeckner, 2006: Ocean circulation and tropical variability in the coupled model ECHAM5/MPI-OM. J. Climate, 19, 3952-3972.

Nakicenovic, N. et al., 2000: ‘IPCC Special Report on Emissions Scenarios’, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Roeckner, E., G.P. Brasseur, M. Giorgetta, D. Jacob, J. Jungclaus, C. Reick und J. Sillmann, 2006: Climate Projections for the 21st century. Max Planck Institute for Meteorologie, Hamburg, Internal Report, 28pp.