Impact of SOlar, Volcanic and Internal variability on Climate (ISOVIC)

Subproject 1:
CHaracterisation of the InternalvARiability of the Atmosphere (CHIARA)

University of Wuppertal, Institute for Atmospheric and Environmental Research
Prof. Dr. Ralf Koppmann, E-mail:
Peter Knieling, E-mail:
Dirk Offermann, E-mail:

Subproject 2:
Modelling and Understanding Solar Irradiance Changes – Phase II (MUSIC-II)

Max Planck Institute for Solar System Research, Göttingen
Dr. Natalie Krivova, Email: natalie*at*
Prof. Dr. Sami K. Solanki, Email: solanki*at*
Dr. Theodosios Chatzistergos, Email: chatzistergos*at*
Dr. Kok Leng Yeo, Email: yeo*at*

Subproject 3:
How did the triad of solar and volcanic forcing, and ocean variability shape the early 19th century and might shape Europe’s future climate?  (TRIAD)
Max Planck Institute for Meteorology (MPI-M), Bundesstr. 53, 20146 Hamburg
Dr. Claudia Timmreck, Email:
Dr. Hauke Schmidt, Email:
Dr. Johann Jungclaus, Email:

ISOVIC is a contribution to the scientific questions:

How does the variability of the sun induce, through changes in circulation, physical processes and chemical composition of the middle atmosphere, and changes in the climate of the troposphere?

How does forcing from the troposphere, in particular anthropogenic influences, couple via effects on the middle atmosphere back into the troposphere and change the climate?

Aims of ISOVIC

An improvement of uncertainties in the prediction of climate change in the next decades is crucial especially regarding political measures for adaptation and mitigation strategies. Besides very specific sources of uncertainties such as changes in radiative forcing due to clouds and aerosol particles or changes in small and large-scale dynamical processes in a warming world a deeper knowledge of possible natural variations and the impact of internal and external forcing is of major importance.

Previous investigations show that internal variability of the atmosphere itself and/or the coupled atmosphere-ocean system seems to have a significant influence on long-term development of atmospheric temperatures. Temporary internal forcings such as volcanic eruptions and long-term external forcings such as changes in solar activity may superimpose and probably enhance these variabilities. The overarching scientific questions of the joint research project are:

  • Based on the analyses of historical data archives and simulations, can we understand the impact of internal variability as well as internal and external forcing on climate variability?
  • Can we use the improved understanding to reduce uncertainties in predictions of the future climate development?
  • Is it possible to disentangle natural effects and anthropogenic influence on climate change?

The proposed project consists of three parts:

  • Investigation of internal variabilities by the analyses of long-term model data sets and measurements (satellite and ground-based data sets) (SP1 CHIARA).
  • Investigation of changes in solar irradiation to improve our understanding of the underlying processesand to greatly reduce the uncertainty in the amplitude of the long-term solar irradiance variability (SP2 MUSIC).
  • Investigation of the impact of volcanic eruptions and changes in solar activity under past, present and future  conditions based on forcing data  from the early 19th century, the best documented period, in which natural forcings have likely dominated climate variability (SP3 TRIAD).

Specific aims of the subprojects

The goal of CHIARA is to investigate the internal variability of the atmosphere, which is present even if there would be no external forcing at all.

Regarding the temperature increase in the framework of climate change, the knowledge of long periodic variations is essential to distinguish between the anthropogenic influence and internal variability of the atmosphere. As Deser et al. (2012) pointed out, the characterization and quantification of uncertainties in climate change projections is of fundamental importance especially for strategic approaches to adaptation and mitigation. The authors emphasize that one specific uncertainty is the internal variability, i.e. the variability of the climate system, which occurs in the absence of external forcing and which arises from non-linear dynamical processes and is an intrinsic property of the atmosphere and probably the coupled ocean-atmosphere-system. Within the first phase of ROMIC (MALODY) we found strong evidence for long-periodic oscillations that extend from ground up to altitudes of 110 km and that are potentially self-excited intrinsic oscillations of the atmosphere. As a contribution to improve decadal climate projections and the development of adaptation and mitigation strategies, with the proposed project we plan to further investigate these oscillations to answer the following scientific questions:

  • What are the horizontal (latitudinal and longitudinal) and seasonal distributions of these oscillations?
  • Are there hemispheric differences or horizontal patterns?
  • Are oscillations waves with horizontal phase speed? 
  • Is there an annual cycle (seasonal differences) of periods, amplitudes and phases?
  • How do these oscillations influence trends in temperature due to climate change?
  • How large are these effects?
  • Is it possible to disentangle anthropogenic and natural influences?
  • What causes the vertical structure of the oscillations?
  • Is there a displacement in the atmosphere? 
  • What are the displacement heights? Can coupling processes be identified?

The main goal of MUSIC-II is to greatly reduce the existing uncertainty in the amplitude of long-term solar irradiance changes and determine how much brighter the Sun is today than during the Maunder minimum by applying two novel and independent techniques that employ

  • the newest 3D magnetohydrodynamic simulations (including a small-scale dynamo) to calculate the brightness of the solar surface for the activity level of recent cycles and in a grand-minimum state
  • historical archives of daily full-disc photographs of the Sun in the Ca II K line over the last century, which is the only existing direct observation of the long-term changes in the surface coverage by bright magnetic features (faculae and plage);

The final outcome of the project will be a robust estimate of the irradiance changes since the Maunder minimum as well as a new time series of TSI, with significantly reduced uncertainties in the secular trend.

The overall goal of TRIAD is to understand the triad of solar, volcanic and ocean variabilityunder pre-industrial and anthropogenic forced conditions by using early 19th century natural forcing reconstructions. We concentrate on the following three points:

To understand the climate of the early 19th century, one of the coldest periods in the last 500 years, and how important the preconditioning of the ocean was in comparison to solar and volcanic forcing, which are both mediated largely by the middle atmosphere. To assess if, in the future climate under high CO2 conditions with enhanced high-latitude warming and a strongly reduced ice cover, strong natural forcing like in the early 19th century may still lead to comparable cooling over Northern Europe. to evaluate the middle atmosphere, its response to natural forcing, and its coupling to tropospheric climate as simulated with the new ICOsahedralNonhydrostatic - Earth System Model (ICON-ESM), using the early 19th century forcing as a test data set.