The Influence of Solar Activity Cycles on Earth's Climate (ISAC)

In cooperation with solar physicists at the Swedish Institute of Space Physics in Lund and climate physicists at the Space and Atmospherics Department, Imperial College, London, the sun-climate group at DTU Space carried out a comprehensive study of the Sun-climate link. The tasks carried out included a literary survey on previously obtained results, identification of relevant solar and climate data, and analysis of correlations between these data.


The emphasis was on direct measurements, i.e., incuding only limited amounts of proxy data, and thus limiting the analysis mainly to the last 50 years and with a strong emphasis on the last 30 years where satellite data have become available both for solar output and for global measurements of Earth's climate.

Correlations between solar output and Earth's climate are evident, but the physical links between these are still unresolved. One obstacle in pin-pointing the physical sun-climate link through analysis of solar-climate correlations is that the different forms of solar output, e.g., radiated energy, ultraviolet radiation, high energy particles, solar wind, and magnetic energy, all vary simultaneously in tune with the solar activity. In the ISAC project multi-regression analysis was employed in order to overcome this obstacle.

The conclusion is that ultraviolet radiation and magnetic energy carried by the solar wind are the most likely candidates for solar influence on Earth's climate. Ultraviolet radiation through influence in the stratosphere, the solar wind through its effect on the amount of cosmic rays received by the Earth and their role on Earth's cloud cover.


The ISAC project was commisioned by The European Space Agency under the Earth Observation Programmes in order to study the link between fluctuations in solar activity and the climate on Earth.


The project is at its final stages, and the final presentation was held at ESA, ESTEC in Holland on 12 April 2007.


The following PDF-reports have been made public:


WP 100   Technical Note 

WP 101   Solar Variability

WP 102   Influences of Solar Variability on Earth

WP 103   Climate Variability Correlated with Solar Activity

WP 104   Modelling of Sun-induced Climate Variability

WP 200   Technical Note 

WP 201   Solar Output

WP 202   Possible Interactions and Modifications 

WP 203   Earth’s Climate 

WP 301,302,401,402  Data analysis and correlations 

WP 403   Stratosphere

WP 304   Data Interprtation - Solar - Technical Note

WP 501a  Role of TSI  

WP 502   Solar wind interaction with magnetosphere and ionosphere 

WP 501b  Role of UV and energetic particles 

WP503    Role of Ionisation

WP 601   External Forcing

ISAC final report