Uppsala University and in United States of America and Canada.
Gjærevoll was a professor of botany at the University of Trondheim from 1958 to 1986, and was a specialist in alpine plants. He was born in Tynset. He held a variety of minister positions in different Norwegian cabinets.
He was Minister of Social Affairs in 1963 and 1963–1965, interrupted by the short-lived cabinet Lyng, Minister of Wages and Prices in the first cabinet Bratteli 1971–1972 and then the first Minister of the Environment in 1972.
As an elected politician he was elected to the Storting from Sør-Trøndelag in 1965. He had previously served in the position of deputy representative during the terms 1958–1961 and 1961–1965.
Trondheim City Council 1952-1967, since 1980, Deputy Mayor 1955-1958, Lord Mayor 1958-1963, 1980-1981. State Nature Conservation Council 1958-1986. Royal Scientific Society since 1951, Academy, of Sciences since 1958.
Married Astri Skaar in 1944.