In the late 1960s Gjessing became increasingly interested in nature conservation so that in the 1970s shifted the focus of his research into environmental impact assessments.
This meant leaving behind his work on pure fluvial geomorphology that had previously brought him acclaim.
In the 1980s the work of Gjessing turned increasingly international with many travels to West and North Africa where he studied environmental issues in arid and semi-arid landscapes.
[2] Gjessing’s personality and approach made him subject of strong and lasting criticism from so-called “rejectionist” even within his own department at the University of Oslo.
Despite their opposition Gjessing managed to establish the course Resource Geography and Landscape Ecology in 1985, attending student demands that had emerged in the 1970s about the need of courses on natural resources and environmental management.