Aarnes jumped in the Continental Cup (COC) from 1996 . Due to good performance at the beginning of the 1997/98 season, he was nominated for the ski jumping World Cup for the first time in 1998 . His first competition in the senior national team was on January 17, 1998 in Zakopane, Poland . With 32nd place, he only just missed the points. In the Continental Cup he finished the 1997/98 season in 8th place in the overall standings. In his first competition in the 1998/99 World Cup season in Lillehammer , he was 23rd for the first and last time to win World Cup points. At the end of the season he was 84th in the overall World Cup ranking.
In 2002, Aarnes tested positive for amphetamine in a doping control and was banned for two years. In 2005 he started again in two competitions in Lillehammer , but ended his active ski jumping career after these.