Climate Variability and Predictability Research in Europe

1999 - 2004

Euroclivar Recommendations

31 October 1998 ( Final version)

Contents (page iii)

Foreword (page v)

Preface and acknowledgements (page vi)

Executive summary (page vii)

Extended summary (page ix)

1 Introduction (p 1)

2 What is CLIVAR?

3 The European perspective

4 European and Atlantic climate variability

5 Global teleconnections

6 Anthropogenic climate change

7 Climate observations

8 Climate modelling

A References

B List of Euroclivar workshops

C Abbreviations and acronyms

D Members of the Euroclivar committee


Important progress in the international CLIVAR (Climate Variability and Predictability) programme - the establishment of programme structure and science plan - was concurrent to the development of the European Commission's Climate Research Programme under the Fourth Framework Programme (1994-1998).

In view of the strong thematic conformity between CLIVAR and the climate research priorities of the EC programme, the creation of Euroclivar, and the implementation of CLIVAR research in Europe was much welcomed by the EC.

The present publication contains discussion and detailed research recommendations resulting from the work of the Euroclivar committee, a number of specialised workshops organised within Euroclivar, and some other scientific contributions.

We congratulate the contributors for this important achievement, which appears very timely in view of the start of the EC's Fifth Framework Programme, in which the CLIVAR thematic is prominent, and where a stronger focusing of the European research effort and an increased level of co-operation is foreseen. We welcome the recommendations, which could be very valuable for the EC programme implementation and likewise for all climate scientists and others interested in climate variability and change. In particular we note with satisfaction the discussion of stronger European collaboration in the field of climate modelling and climate change assessment - pertinent in a post-Kyoto perspective.

Our sincere thanks are due to Dr. Gerbrand Komen, for the enthusiasm, energy and dedication he has put into coordinating and advancing the work in Euroclivar.

Anver GHAZI and Ib TROEN
Climate and Natural Hazards Unit
Environment and Climate Programme
European Commission, Brussels


Preface and acknowledgements

Cold European winters follow mild ones in a seemingly erratic way; periods of drought follow periods of abundant precipitation. Similar whimsical fluctuations occur in the ocean, where currents and seawater properties keep varying all the time, and in polar regions, where ice coverage is subject to continuous change. In the tropics, interactions between the atmosphere and the ocean lead to large fluctuations - El Niño is the best known example -, with worldwide effects. All of these phenomena are currently being perturbed by human emissions of greenhouse gases, which appear to modify climate on a global scale. Both natural and anthropogenic climate variations influence many aspects of life on our planet.

We begin to understand the mechanisms behind these climate variations. The atmosphere, the ocean and the cryosphere are very complex systems, interacting with each other in many intricate ways. The ensemble - the climate system - is of an incredible complexity.

Our recommendations for a strong European contribution to Climate Variability and Predictability research are primarily made to the European Union. However, we hope that they are also useful to national organisations and that they will stimulate the discussion among European scientists.

This report is based on discussions in the Euroclivar committee and on results of eight specialised Euroclivar workshops. For each workshop objectives were carefully discussed beforehand and the experts to be invited were selected with care so as to have an optimal spread in scientific input while still limiting the number of participants to allow for easy discussion. When necessary experts from outside Europe were invited. In some cases workshops were jointly organised with other bodies. The present document can only summarise the main results of the workshops. More details are given in separate workshop reports.

I would like to thank the members of the Euroclivar committee, especially Ib Troen from the Environment and Climate Programme (1994 - 1998) of the European Commission, and those members who have put time and energy in the organisation of workshops. The enthusiasm of the workshop participants, and all others who helped in making the workshops and meetings successful, is gratefully acknowledged. Special thanks go to Fons Baede, Gerrit Burgers, Lydia Dümenil, Martin Fischer, Harry Fijnaut, Lesley Gray, Serge Gulev, Phil Jones, Wibjörn Karlén, Michael Lautenschlager, Franco Molteni, Alan O'Neill, Jan Polcher, Alexander Polonsky, Stefan Rahmstorf, David Stephenson, Erich Roeckner, Catherine Senior, Simon Tett, Chris Thorncroft, Neil Ward and David Webb for their comments and contributions. I also gratefully acknowledge help from and stimulating discussions with Hartmut Grassl, Valery Detemmerman, Andreas Villwock and John Gould, from the International CLIVAR and WCRP staff, Kevin Trenberth and Allyn Clarke, co-chairs of the CLIVAR Scientific Steering Group, and Larry Gates, chairman of the Joint Scientific Committee of the WCRP.

Gerbrand KOMEN

Euroclivar coordinator

Executive summary

This document contains recommendations for European research on global climate variability and predictability, as a European contribution to the global CLIVAR programme. A better understanding of climate is of great importance for Europe for a number of reasons: 1. Natural fluctuations of the climate of Europe have many very significant consequences for safety, health, infrastructure, agriculture, energy, economy. 2. Natural climate fluctuations elsewhere in the world have European implications through geophysical, socio-economic and political mechanisms. 3. Improved prediction and detection of anthropogenic climate change will provide a firmer scientific basis for active emission, mitigation and adaptation policies. The mechanisms activated under the international post-Kyoto negotiations (joint implementation and emission trading) will, inter alia, demand knowledge of global climate patterns.

Scientific issues

Natural climate fluctuations and human-induced climate change are intricately related and need to be studied together. Euroclivar recommends that high priority be given to the following topics: 1. European and Atlantic variability; 2. Global teleconnections; and 3. Anthropogenic climate change.

The climate in the North Atlantic/European domain exhibits significant variability on interannual and decadal time scales, involving interactions between the atmosphere and ocean circulation. At the same time this region is affected by major teleconnections linked to phenomena in the tropical atmosphere/ocean/land system, such as El Niño, African climate variability and the Asian monsoon. There are discrepancies between predictions of climate change made by different models which need to be understood and reduced. The scientific basis for detection and attribution of climate change must be improved.

The predictability of the climate system on time scales from seasonal to centennial needs to be quantified and models suitable for climate prediction must be developed.

Climate observations

To achieve the Euroclivar objectives, the establishment of an integrated observational network is imperative. This network, to be implemented in cooperation with nations adjacent to the Atlantic, should include: 1. an extensive network of profiling floats in the Atlantic; 2. an operational tropical Atlantic array of moored atmosphere/ocean observing stations (PIRATA); 3. basin-wide measurements of the Atlantic water mass and circulation variability at critical latitudes; 4. continuation, at the present level, of the ocean/atmosphere observations with voluntary observing ships; and 5. continuous contribution of satellites to the global coverage of the ocean and atmosphere. In addition, past climate variability needs to be reconstructed, using both the instrumental and the palaeoclimatic records.

A European Climate Computing Facility

Reliable regional climate change predictions cannot be achieved without enhanced European collaboration and substantial increases in computing resources. These are needed so that multi-century simulations can be made with sufficient complexity that important climatic features, physical processes and regional details are resolved. In addition, ensembles of integrations must be made to estimate the impact on climate predictions of uncertainties in initial conditions and model formulation. The computational requirements for such simulations cannot be met from purely national resources. It is therefore strongly recommended that a European Climate Computing Facility be established.

Extended summary

Understanding climate change and variability remains a major scientific challenge, notwithstanding significant progress in the last decade. The World Climate Research Programme has established CLIVAR (Climate Variability and Predictability), a major research programme to understand and predict, to the extent possible, climate variations on time scales from seasonal to centennial, arising from both natural and anthropogenic causes.

European scientists are at the forefront of climate research. However, there is a need to coordinate this research in Europe. Euroclivar provides a vehicle for such coordination. Furthermore, a better understanding of climate is of great importance for Europe. There are three broad categories of reasons:

We propose priorities for climate variability and predictability research in Europe, as a European contribution to the global CLIVAR programme. We distinguish three main areas of research, namely

In addition, we discuss two cross-cutting aspects, namely

European and Atlantic climate variability

A substantial proportion of the climate variability in the Atlantic/European region is associated with the North Atlantic Oscillation (NAO) pattern linking the Iceland area and the Azores region. The NAO has undergone major low frequency variations this century, possibly as a result of oceanic, anthropogenic or even stratospheric processes.

Some of the low frequency variability in the North Atlantic Ocean arises as a response to fluctuations in the NAO. The NAO also influences the formation of deep water in the Greenland/Iceland/Norwegian and Labrador seas, which in turn influences the strength of the Atlantic Meridional Overturning Circulation (MOC). Although the MOC is a phenomenon of basin-to-global scale, its dynamics and in particular its variability may be controlled by rather small-scale processes associated with the formation and spreading of deep waters. Model results and palaeo-oceanographic data indicate long-term fluctuations in the overall strength of the MOC with transitions between fundamentally different states of the MOC sometimes taking place within decades. Although it appears that changes in the MOC can occur naturally, there is also the possibility that they could be triggered by anthropogenic emissions and could lead to significant changes for European climate.

In the tropical Atlantic also, there is substantial variability on interannual and decadal time scales. Although the tropical and higher latitudes are frequently considered separately, they overlap and are unlikely to be independent. There is also a relation between the tropical Atlantic variability and ENSO, but the mechanisms are unclear.

The predictability of climate fluctuations in the Atlantic/European region needs to be established. Improved understanding of climate variability is essential to identify the limits of predictability and for establishing confidence in attribution and prediction of climate change.

A modelling and observational programme is proposed which consists of the following elements:


Numerical modelling studies

Global teleconnections

Climate variability in Europe, the Mediterranean and the Atlantic is linked through so-called teleconnections to remote phenomena in the tropical atmosphere/ocean system, in particular to ENSO, the Asian Summer Monsoon, and to several components of the African and American climate system. Thus it is necessary that these components of the climate system are studied in their own right. We make the following set of recommendations:

El Niño/Southern Oscillation (ENSO)

Asian Monsoon

African climate variability

Anthropogenic climate change

Predictions of anthropogenic climate change must be improved in order to guide both emission policies and adaptation to human-induced climate change. Predictions are made with the help of coupled atmosphere/land-surface/ocean/sea-ice models, driven by projected greenhouse gas concentrations, atmospheric aerosol loadings and other external factors. Emphasis must be on quantifying uncertainty through sensitivity studies and reducing uncertainties through model improvement. In addition, research is needed to improve the scientific basis of detection and attribution of climate change and to improve uncertainty estimates, taking advantage of advances in modelling and observations. We make the following recommendations:

Reducing uncertainty in predictions

The uncertainty in predictions, currently ± 50 % in global mean temperature change must be reduced by improving modelling through

Improving predictions

Predictions must be improved through

Detection and attribution of climate change

Our ability to attribute recent climate change must be improved by

More specific recommendations are made in the main body of the text (section 6.3) and in a separate workshop report (Euroclivar workshop on Climate Change Detection and Attribution).

Note that greatly enhanced computer capacity will be required to run ensemble simulations and to increase model resolution.

Climate observations

CLIVAR needs improved and expanded observational data sets aided by new technologies, and the systematic compilation of existing sparse data sets. High-resolution, three-dimensional data for the atmosphere are available only for the past 18 years but will soon be extended at lower quality for the previous 20 years. The vast majority of existing ocean data are from the upper layers; data for the deep ocean are relatively sparse. Data for other elements of the climate system (atmospheric chemistry, biogeochemical cycles, sea and land ice) are also patchy. Land surface temperature and pressure data can generally be constructed back to the late 19th century but in some regions such data begin only 40 years ago or less. Before that time we have to rely on indirect (proxy) data. Euroclivar proposes the following research activities.

New observations

Analysis and reanalysis of recent past climate

Palaeo data

Climates from before the recent instrumental period must be deduced from proxy (non-instrumental) records. These include tree rings, deep-sea sediments, corals and ice cores and involve isotopic, geochemical and micropalaeontological analysis.

Data availability

Climate modelling

In the foregoing recommendations numerical modelling experimentation played a key role. Models are essential tools for the study of both anthropogenic climate change and natural climate variability. Projections and predictions of future climate cannot be addressed without the use of numerical models. Models also give insight into the mechanisms that play a role in the real climate system. They complement observations and are important tools for the support of field programmes and the design of observational systems. They facilitate the interpretation of observations. Models can also be used to study the response of the climate system to particular forcings and processes, which could not be isolated in the real world. However, such models still suffer from substantial systematic deficiencies. Progress in reducing such deficiencies is hampered by insufficient computer resources.

Modelling strategy

European integration

We recommend a better integration of the European modelling effort with respect to human potential, hardware and software.