His interest in solar activity began in August, in his tent, when he experienced an extreme solar storm:[3] "I was in Greenland, on my first assignment in my new job as geophysicist at the Danish Meteorological Institute, setting up a chain of magnetometer stations on the west coast... watching ink pens of my recorder going so wild that they nearly tore the paper chart apart -- we had no digital recording at that time -- and I wondered whether such big events could also have an influence in the lower atmosphere, on weather and climate.
He was an adjunct professor of geophysics and space physics 1996 to 2006 [4] at the Niels Bohr Institute of University of Copenhagen[5] and has authored over 140 research articles or books.
[3] The New York Times reviewed the Science article on 5 November 1991, stating, "While the correlation established by Dr. Friis-Christensen and Dr. Lassen falls short of definite proof, a number of scientists nevertheless called it remarkable in its close fit between the solar and temperature trends.
[11][12] In 2009, a number of leading experts, including one Nobel laureate, concluded that the graphs of Friis-Christensen and Svensmark showing apparent correlations between global warming, sunspots and cosmic rays were deeply flawed.
[13] In 1997, Friis-Christensen and Henrik Svensmark revived suggestions of a possible link between galactic cosmic rays and global climate change assisted by solar wind intensity variation, which they termed cosmoclimatology.